Milk production of cows grazing pasture supplemented with grain mixes containing canola meal or corn grain or both over the first 100 days of lactation

Grain mixes varying in proportions of wheat grain, barley grain, canola meal and corn grain were fed to grazing dairy cows in early lactation to determine the contribution of canola meal and corn grain to milk yield, body weight (BW), body condition score (BCS), eating behavior and blood serum metabolite concentrations. The experiment used 80 multiparous, seasonally calving Holstein-Friesian dairy cows during the first 100 d of lactation, the treatment period, and over the subsequent carryover period of 100 d, during which all cows were fed a common diet. Cows were divided into 4 cohorts (blocks) based on calving date and within each cohort, 5 cows were randomly allocated to each of the 4 treatments. Dietary treatments included disc milled grain mixes comprising (on a dry matter (DM) basis) 1) a control treatment of wheat (25%) and barley (75%); 2) wheat (25%), barley (50%) and canola meal (25%); 3) wheat (25%), barley (50%) and corn (25%), and 4) wheat (25%), barley (25%), canola meal (25%), and corn (25%). Treatment diets were introduced at 19 d in milk (DIM) ± 4.7 d which included a 7-d adaptation period and were applied up until 100 DIM. Each grain mix was fed at 9 kg DM/cow per d, offered twice daily, in equal proportions in the parlor at milking times. In addition to the grain mix, all cows grazed perennial ryegrass pasture at a daily allowance of approximately 35 kg DM/cow per d (measured to ground level). Results were analyzed in terms of corn and canola presence or absence in the diet. Including canola meal in grain mixes increased grain intake and pasture intake by 0.6 and 2.1 kg DM/cow per d, respectively, resulting in an increased milk yield of 2.6 kg/cow per d during the first 100 d of lactation. Including canola meal also increased yields of milk fat and protein, and concentrations of milk fat, as well as increasing mean BW and BCS over the 100 d. The inclusion of canola meal in the grain mixes also resulted in greater blood serum β-hydroxybutyrate and urea concentrations, compared with feeding grain mixes that did not contain canola meal. The inclusion of corn grain provided no milk production benefits and did not change BW, BCS or any feeding behavior variables. There were no carryover effects on milk production from either canola meal or corn grain after the treatment period. In summary, the results demonstrate that the provision of canola meal in grain mixes can improve milk production and increase mean BCS. Further, there are no benefits to milk yield when a proportion of barley is substituted for corn, in a wheat and barley grain mix fed to grazing dairy cows in early lactation. However, these results are dependent on the level of inclusion and the feeding system employed.

Effect of forage type on swallowed bolus mass and a method for counting swallows in dairy cattle

Dry matter intake (DMI) is a primary determinant of milk production in grazing dairy cows and an ability to measure the DMI of individual cows would allow herd managers to formulate supplementary rations that consider the amount of nutrients ingested from grass. The 2 related aims of this experiment were to define the mean number of swallowed boli and mass of the swallowed boli in Holstein-Friesian dairy cattle offered a variety of forages commonly fed in the dairy industry of southeastern Australia, and to evaluate 2 indirect methods for counting the number of swallows. Twelve ruminally-fistulated, lactating Holstein-Friesian cows were randomly assigned to 3 replicated 4 × 4 Latin square designs and offered 4 forages: fresh chicory (FC), fresh perennial ryegrass (RP), alfalfa hay (AH), and perennial ryegrass silage (RS). The experiment was conducted over 28 d with each of 4 periods consisting of 7 d with 3 d of measurement. Forage diets were offered to individual cows following the partial evacuation of the rumen. The first 20 min after forage was offered constituted the measurement period, during which all swallowed boli were manually captured by samplers who placed their hand through the ruminal fistula and over the cardia entrance of the rumen of each cow. Concurrently, microphones and video cameras were used for the indirect measurement of swallows. The average swallowed bolus mass overall was 17.4 g dry matter (DM) per bolus with the lowest mass observed in cows offered FC (8.9 g DM/bolus), followed by RP (14.9 g DM/bolus), compared with cows offered AH (23.6 g DM/bolus) and RS (22.3 g DM/bolus). The swallowing rate was greater in cows offered FC (78 swallows/20 min) than in cows offered RP, AH, and RS (62.3 swallows/20 min). The audio recording method showed greater concordance (Lin's concordance correlation coefficient = 0.90) with the physical capturing of the boli through the rumen, than the video recording method did (Lin's concordance correlation coefficient = 0.54). It is concluded that the mass of the swallowed boli is related to forage type and that using a microphone attached to the cow's forehead can provide an accurate measure of the number of swallows when verified against the actual number of swallows counted by manual interception of the boli at the rumen cardia.

Using estimated nutrient intake from pasture to formulate supplementary concentrate mixes for grazing dairy cows

In pasture-based dairy systems, feeding a complex concentrate mix in the parlor during milking that contains cereal grains and protein supplements has been shown to have milk production advantages over feeding straight cereal grain. This experiment had the aim of testing whether further milk production advantages could be elicited by adjusting the composition of the concentrate mix in an attempt to match the expected nutrient intake from pasture during late spring. The experiment used 96 lactating dairy cows, grazing perennial ryegrass pasture offered at a target allowance of 30 kg of dry matter/cow per day (to ground level) during late spring (mid October to November) in southeastern Australia. Cows were allocated into 3 replicates of 4 treatment groups, with 24 cows in each treatment. Each treatment group was offered 1 of 4 dietary treatments in the parlor at milking: control consisting of crushed wheat and barley grains; formulated grain mix (FGM) consisting of crushed wheat, barley, and corn grains and canola meal; designer grain mix 1 (DGM1) consisting of the same ingredients as the FGM grain mix but formulated using the CPM Dairy nutrition model to take into account the expected nutrient intake from pasture; and designer grain mix 2 (DGM2) consisting of the same ingredients as DGM1 but with canola meal replaced by urea and a fat supplement (Megalac, Volac Wilmar, Gresik, Indonesia). Concentrate mixes were offered at 8.0 kg of dry matter/cow per day, except for DGM2 cows, which were offered 7.5 kg of dry matter/cow per day. The experiment ran for a total of 28 d; after a 14-d adaptation period, nutrient intake, milk production, and body weight were measured over a 14-d measurement period. Milk yield (kg) of cows fed the FGM diet was greater than that of the control cows but was not different from that of the DGM1 and DGM2 cows. However, milk fat and protein yields (kg) were greater for cows fed the FGM diet than for all other diets. There was no difference in estimated daily pasture or total dry matter intakes between the 4 treatment groups, despite cows fed the DGM2 treatment consuming less of the concentrate mix (average 6.5 kg of dry matter/cow per day when offered 7.5 kg of dry matter/cow per day). This research has demonstrated the potential for using a nutrition model to take into account the expected nutrient intake from pasture to formulate a concentrate mix (DGM1) to achieve similar milk yields, but also highlighted the need for near real-time analyses of the pasture to be grazed so as to also capture benefits in terms of milk fat and protein yield.

Quantifying the ruminal degradation of nutrients in three cultivars of perennial ryegrass (Lolium perenne L.) sampled during early spring and summer

Context The Australian dairy industry is characterised by pasture-based feeding systems, where grazed pasture is commonly supplemented with cereal grain to increase milk production of dairy cows. Perennial ryegrass (PRG; Lolium perenne L.) is the most commonly used pasture species, with a wide range of cultivars available. However, the nutritive characteristics and the degradation of nutrients in individual PRG cultivars grown in different environments in Australia are unknown, and significant variation between cultivars may impact on supplementary nutrient requirements. Aims The objective of this experiment was to quantify the extent of ruminal degradation of nutrients in three contrasting PRG cultivars (Bealey NEA2, Trojan NEA2 and Victorian SE) harvested during early spring and summer from Gippsland, northern Victoria and south-west Victoria in Victoria, Australia. Methods Degradation parameters were determined by in situ incubation in the rumens of non-lactating, rumen-fistulated Holstein–Friesian cows for 72 h using a nylon bag technique. Key results During both seasons, Bealey NEA2 had the greatest effective degradability of crude protein and neutral detergent fibre compared with Trojan NEA2 and Victorian SE. Cultivars harvested during early spring had greater effective degradability of crude protein and neutral detergent fibre, and a greater amount of rumen degradable protein compared with cultivars harvested during summer. Cultivars harvested from Gippsland had greater crude protein and neutral detergent fibre effective degradability, as well as a greater amount of rumen degradable protein, whereas cultivars harvested from northern Victoria had a greater amount of undegraded dietary protein. Conclusions These results demonstrate that the ruminal degradation of PRG cultivars declines with increasing maturity, and that there are differences between cultivars and regions; however, differences between seasons are of a greater magnitude and are more important to consider when formulating optimal supplementary grain rations. Implications This research has positive implications for farmers who will be able to understand the degradation of nutrients in PRG, and the amounts of rumen degradable protein and undegraded dietary protein available from pasture during each season. Farmers will be able to use this information to formulate supplementary grain rations that complement the nutrients from pasture and optimise milk production.

A whole-farm investment analysis of a partial mixed ration feeding system for dairy cows

Aim A dairy farm in south-west Victoria was analysed to discern the impact on profit and risk of changing from a feeding system in the base case where grain was fed in the dairy and forage in the paddock, to a partial mixed ration (PMR) or a formulated grain mix (FGM) feeding system. Context A PMR feeding system involves feeding a well formulated mixed ration to a grazing dairy herd and typically requires the use of specialised machinery to mix and feed out the forage and grain components of the ration together onto a feed pad. In a FGM feeding system, the same formulated ration fed in the PMR system is used, but the grain component of the ration is fed using the existing feeding system in the dairy with the hay component fed in the paddock. Method The analysis used data from experiments recently performed to establish milk responses to mixed ration feeding under Australian conditions. The case study farm comprised 244 ha and a herd of 420 self-replacing Holstein-Friesian cows that calved from May to July. The herd feeding system was based on grazed pasture, grain fed in the dairy at milking and hay fed in the paddock. Supplementary feed comprised ~50% of metabolisable energy in the diet of the milking cows. The pre-existing feeding system was altered to incorporate either a PMR system or a FGM system. An increased herd size of an extra 100 cows, plus the PMR or FGM systems, was also tested. Key results All systems analysed were more profitable than the base case. Increasing the herd by 100 cows was the most profitable option for both the PMR and FGM systems, but intensifying the system by increasing cow numbers also had the most variability in profit. Conclusions and implications The FGM system was the most profitable system because milk production could be increased without the costs of extra labour, depreciation and repairs and maintenance associated with using a mixer wagon to feed the ration. The FGM system presents an option for farmers to expand or intensify their systems without needing to construct a feed pad or invest in extra machinery and equipment.

Defining the key attributes of resilience in mixed ration dairy systems

Dairy feeding systems in Australia and New Zealand have seen an increase in the use of mixed rations to manage variability in climate and market conditions and enable a certain degree of resilience in the operating environment. In this review, resilience was defined as the ability of the farm system to respond to challenges, optimise productivity and profitability for a given set of circumstances, and persist over time. Specific attributes of a dairy system that contribute to resilience were considered as flexibility, consistency, adaptation, sustainability and profitability. A flexible forage base that uses water efficient forage species provides a consistent supply of nutrients from home-grown forages across the year and is a key driver of resilience. Consistent milk production from purchased concentrates adds value to the forage base and will ensure that the system is profitable in the long term. Appropriate investment in infrastructure and careful management of debt has a positive impact on technical and financial efficiency and improves overall economic performance and resilience of the system. Nutrients, feed wastage, cow comfort and welfare were also identified as key areas to focus on for improved sustainability. Future research investigating the interaction between forages and concentrates, and the subsequent milk production response will be important for the future resilience of mixed ration systems. Adaptive management at a tactical and strategic level across several technical areas will further underpin the resilience of a mixed ration dairy system, and minimise the impact of climate and price variability. This will have flow on benefits to animal welfare and resource sustainability, which will have a positive impact of the public perception of these systems within the Australian and New Zealand dairy industries.

A quantitative case study assessment of biophysical and economic effects from altering season of calving in temperate pasture-based dairy systems

In theory, a late winter-early spring calving date in temperate grazing systems best matches pasture supply and herd demand, thereby minimizing the need for nonpasture feeds and maximizing profitability. We used a quantitative case study approach to define the effects of season of calving on biophysical and financial performance in a grazing system without the confounding effects of imported feeds (i.e., milk production directly from grazed pasture). A 2-yr production system experiment was established to quantify the effects of changing onset of seasonal calving (i.e., planned start of calving; PSC) from winter (July in the Southern Hemisphere) to spring (October), summer, (January), or autumn (April) on pasture and animal production and profitability. Eighty Holstein-Friesian cows were randomly allocated to 1 of 4 PSC treatments, each of which had a different PSC [mean calving date of January 10 (JAN), April 10 (APR), July 10 (JUL), or October 10 (OCT)]. Data were analyzed for consistency of treatment response over years using ANOVA procedures with year, PSC treatment, and year × PSC treatment interactions as fixed effects. Collated biological data and financial data extracted from a national economic database were used as fixed variables to model the financial performance for the different treatments. A stochastic risk analysis was undertaken, where historical pasture growth and milk price data were used to estimate the probability distributions for stochastic input variables. Gross farm revenue and operating profit per hectare were modeled under 2 scenarios: (A) milk price did not include a premium for milk supplied during the winter, and (B) milk price included a realistic premium for milk supplied in winter. Annual and seasonal pasture growth did not differ between treatments, but the pasture growth (kg of dry matter/ha) and profile of the JUL treatment best matched the lactation nutrient demand profile. In comparison, profiles for JAN, APR, and OCT calving treatments had periods of greater surplus and deficit due to the time of calving and herd demand relative to the pasture growth profile. As a result, the JAN and OCT treatments conserved more pasture as silage and cows consumed a larger proportion of their annual diet as silage. Although the amount of silage conserved and consumed did not differ between the JUL and APR calving treatments, the timing of the silage consumption was different, with silage making up a greater proportion of the diets in the APR treatment 1 to 90 and 91 to 180 d postcalving and being offered to the JUL calving treatment only 271 to 365 d postcalving. As a result of differences in the quantity and proportion of pasture and pasture silage in the lactating diet, the JUL treatment herd tended to produce greater milk, 4% fat-corrected milk, fat, protein, and lactose yields (kg/cow) than the other PSC treatments, which did not differ from each other. Operating expenses per hectare did not differ materially between calving date scenarios, but operating expenses per kilogram of fat-corrected milk and kilogram of fat and protein were 15 to 20% less in the JUL treatment. With or without a realistic winter milk premium, gross farm revenue and operating profit per hectare were greater in the JUL treatment than in the APR treatment, which had greater revenue and profitability than the remaining 2 calving date treatments. In summary, our results indicate that a PSC in late winter is most profitable in a grazing system not importing feed, with or without a realistic price incentive scheme.

Modification of the sterol profile in milk through feeding

The fortification of milk with phytosterols is an increasingly common practice to enhance the sterol profile and offer consumers potential health benefits. This study investigated whether cattle feed can influence the profile of phytosterols and cholesterol in the milk produced as an alternative to direct fortification of milk. Five experiments were performed using feeds commonly used by Australian dairy farmers and selected formulated rumen-protected feeds. Statistical significances were observed for some individual plant sterols and cholesterol in milk under these differing feeding regimens compared with the respective controls. In the case of the phytosterols, where the daily recommended consumption is typically 2 g per day, the total phytosterols were <0.12 mg/100 mL of milk. An experiment using a rumen-protected feed with high phytosterol levels suggested a decreased transfer of cholesterol to the milk by as much as 20%, although further work is required to confirm these preliminary results. Overall, the study suggests that different feeding practices have minimal effect on the resulting sterol profile of the milk.

Milk production of cows grazing pasture supplemented by a partial mixed ration with or without canola meal

Milk production responses were measured in grazing cows offered mixed rations with or without canola meal. Experiments were conducted in spring (Experiment 1; early lactation) and autumn (Experiment 2; late lactation). The experiments used 140 (Experiment 1) or 96 (Experiment 2) Holstein-Friesian multiparous dairy cows that had calved in late winter/early spring. Each experiment lasted 28 days including a 14-day adjustment period and a 14-day measurement period during which intake and milk production was measured. In each experiment, there were two dietary treatments: PMR: cows grazed a restricted pasture allowance (10–15 kg DM/cow per day, measured to ground level) supplemented with a PMR comprising wheat grain (60%, DM basis), lucerne hay (21%) and maize grain (19%); and PMR+C: cows were fed the same as the PMR cows, but some wheat grain in the PMR was replaced with solvent-extracted canola meal so that it comprised wheat grain (39%, DM basis), lucerne hay (21%), maize grain (19%) and canola meal (21%). The two treatments were randomly allocated to half the cows in each experiment. Cows were then further allocated into 10 groups of 7 cows (Experiment 1) or 8 groups of 6 cows (Experiment 2). Two groups of cows were assigned to receive a different amount of each ration: 8, 10, 12, 14 or 16 kg DM total supplement/cow per day for Experiment 1 and 6, 8, 10 or 12 kg DM total supplement/cow per day for Experiment 2. In Experiment 1, yields of energy corrected milk (ECM), milk fat, and milk protein were greater for PMR+C cows than PMR cows when 12 kg/cow per day of supplement or more was offered. Milk protein concentration was greater in PMR+C cows than PMR cows but only when 16 kg DM supplement/cow per day was offered. These changes in milk yield and composition were associated with increases in the intakes of pasture, supplement and total DM intake in the PMR+C cows compared with the PMR cows. In Experiment 2 there were no differences in milk yield or composition between PMR and PMR+C cows at any amount of supplement offered, nor were there any differences in intakes of pasture, supplement or total DM intake. It is concluded that replacing some of the wheat in a well-formulated PMR with canola meal can stimulate DMI and increase per-cow production of ECM when high amounts of supplement are fed in early lactation, but not late lactation.

Effect of wheat adaptation strategies on rumen parameters and dry matter intake of late lactation dairy cows

The effects of a major dietary change on ruminal fluid pH, volatile fatty acid (VFA), lactate and ammonia concentrations, dry matter intake (DMI) and milk yield were measured in 32 dairy cows in late lactation. All cows were initially fed 100% lucerne hay cubes and were then gradually introduced to a diet with wheat comprising 40% of total dry matter (DM) and lucerne hay cubes, the remainder. Wheat was gradually substituted for lucerne via one of four strategies, (1) in six small increments (each 6.7% of total DM) over 6 days; (2) in six small increments (each 6.7% of total DM) over 11 days; (3) in three large increments (each 13.3% of total DM) over 6 days; or (4) in three large increments (each 13.3% of total DM) over 11 days. The introduction of wheat in six small increments resulted in a lower daily minimum ruminal fluid pH (pH 5.95) when compared with using three large increments (pH 6.05). Despite this difference none of the treatments exhibited a ruminal fluid pH that would have compromised ruminal function, nor were there differences in DMI (19.7 kg DM/cow.day) or milk yield (16.0 kg/cow.day). Additionally, there were no differences between ruminal fluid VFA, lactate or ammonia concentrations. It is speculated that the properties of the lucerne cubes, including a high buffering capacity, helped the ruminal contents resist the pronounced declines in pH often seen with the fermentation of large amounts of wheat. Under the conditions of this experiment the wheat adaptation strategies used did not lead to any critical differences in rumen parameters. These results suggest that changes to rumen function are driven not only by the characteristics of the concentrate being introduced but also by those of the forage.

Forage type influences milk yield and ruminal responses to wheat adaptation in late-lactation dairy cows

The effects of different wheat adaptation strategies on ruminal fluid pH, dry matter intake (DMI) and energy-corrected milk (ECM) were measured in 28 late-lactation dairy cows. Cows were fed either perennial ryegrass (PRG) hay or alfalfa hay and had no previous wheat adaptation. Wheat was gradually substituted for forage in 3 even increments, over 6 or 11 d, until wheat made up 40% of DMI (∼8 kg of dry matter/cow per day). We found no differences in DMI between adaptation strategies (6 or 11 d) within forage type; however, cows fed alfalfa hay consumed more overall and produced more ECM. The rate of ruminal pH decline after feeding, as well as the decrease in mean, minimum, and maximum ruminal pH with every additional kilogram of wheat was greater for cows fed alfalfa hay. Cows fed alfalfa hay and on the 6-d adaptation strategy had the lowest mean and minimum ruminal fluid pH on 3 consecutive days and were the only treatment group to record pH values below 6.0. Despite ruminal pH declining to levels typically considered low, no other measured parameters indicated compromised fermentation or acidosis. Rather, cows fed alfalfa hay and adapted to wheat over 6 d had greater ECM yields than cows on the 11-d strategy. This was due to the 6-d adaptation strategy increasing the metabolizable energy intake in a shorter period than the 11-d strategy, as substituting wheat for alfalfa hay caused a substantial increase in the metabolizable energy concentration of the diet. We found no difference in ECM between adaptation strategies when PRG hay was fed, as there was no difference in metabolizable energy intake. The higher metabolizable energy concentration and lower intake of the PRG hay meant the increase in metabolizable energy intake with the substitution of wheat was less pronounced for cows consuming PRG hay compared with alfalfa hay. Neither forage type nor adaptation strategy affected time spent ruminating. The higher intakes likely contributed to the lower ruminal pH values from the alfalfa hay treatments. However, both forages allowed the rumen contents to resist the large declines in ruminal pH typically seen during rapid grain adaptation. Depending on the choice of base forage, rapid grain introduction may not result in poor adaptation. In situations where high-energy grains are substituted for a low-energy, high-fiber basal forage, rapid introduction could prove beneficial over gradual strategies.

Plasma glucose and nonesterified fatty acids response to epinephrine challenges in dairy cows during a 670-d lactation

This experiment investigated the metabolic response to a 2-dose epinephrine challenge of dairy cows undergoing an extended lactation. Twelve multiparous Holstein-Friesian cows that calved in late winter in a seasonally calving pasture-based dairying system were managed for a 670-d lactation by delaying rebreeding. In each of four 40-d experimental periods commencing at 73, 217, 422, and 520 (±9.1) d in milk (DIM), cows were offered a diet of perennial ryegrass (73 and 422 DIM) or pasture hay and silage (217 and 520 DIM), supplemented with 1 (CON; n = 6) or 6 kg of grain (GRN; n = 6) as a ration. Daily energy intake was approximately 160 and 215 MJ of metabolizable energy/cow for the CON and GRN treatments, respectively. At all other times, cows were managed as a single herd and grazed pasture supplemented with grain to an estimated daily total intake of 180 MJ of metabolizable energy/cow. Cows were fitted with a jugular catheter during the final week of each experimental period. Two doses of epinephrine (0.1 and 1.6 µg/kg of body weight) were infused via the catheter 2 h apart to each cow at approximately 100, 250, 460, and 560 DIM. Blood plasma concentrations of glucose and nonesterified fatty acids (NEFA) were measured before and after infusions. Cows in the GRN treatment had greater milk yield, milk fat and protein yields, and body weight than cows in the CON treatment. The maximum plasma glucose concentration was observed at 100 DIM for both the low and high doses of epinephrine. Thus, sensitivity and responsiveness to exogenous epinephrine were greater during early lactation, coinciding with increased priority of milk synthesis. Both the sensitivity and responsiveness to epinephrine decreased with decreasing milk yield, as measured by the acute appearance of NEFA in the plasma. Increased plasma glucose and NEFA clearance rates before 300 DIM indicated greater uptake of these substrates by the mammary gland for milk synthesis in early and mid lactation. These results support previous findings that major changes occur in terms of adipose tissue metabolism during extended lactations. Overall, sensitivity to epinephrine was not affected by diet, but responsiveness was greater in cows fed the GRN diet. The endocrine regulation of nutrient partitioning throughout traditional and extended lactations is complex, with many interactions between stage of lactation, diet, and milk yield potential.

Evaluating the economics of short-term partial mixed ration feeding decisions for dairy cows

Recent research in Australia has measured the marginal milk production responses of cows grazing perennial-based pastures to supplements offered as a partial mixed ration (PMR). In the present study, the milk responses to PMR feeding developed under a restricted pasture allowance were used to examine the contribution to farm profit of decisions about short-term feeding (weekly, monthly). A short-term, or tactical, decision was considered to be one where the infrastructure and equipment needed to mix and feed out a formulated ration were already available. The decision was, therefore, the choice of whether to feed supplements as grain in the dairy at milking and forage in the paddock, or to feed the supplements as a mixed ration on a feed pad. Both of these options were assumed to exist for the farmer decision-maker, with the comparison of rations being based solely on the costs of supplement and milk income. The Control diet in the experiments comprised cereal grain fed in the dairy and pasture silage fed in the paddock, simulating a situation where pasture available for grazing was limiting. The PMR diet consisted of cereal grain, maize grain, maize silage and lucerne hay combined in a mixer wagon and fed on a feed pad. The PMR + canola diet was similar to the PMR diet, but included canola meal. The profitability of the diets for different amounts of supplement intake was compared by estimating the total income from milk produced minus the cost of the supplements. The results indicated that feeding the diet comprising PMR plus canola meal in early lactation contributed more to farm profit than did the Control diet of feeding grain in the dairy and forage in the paddock, or PMR feeding without canola meal, because of higher milk production. At a supplement intake of 12 kg DM/cow.day, the PMR + canola diet added AU$0.97/cow.day and AU$2.11/cow.day more to profit than the Control and PMR without canola meal diets, respectively. For a farm already equipped with a feed pad and mixer wagon, the benefits of feeding a mixed ration exceed the costs in early lactation. In late lactation, each diet made similar contributions to farm profit because of similar milk production.

Dry matter intake and feeding behaviour of grazing dairy cows offered a mixed ration with or without canola meal

Dry matter intake and feeding behaviour were measured in grazing dairy cows fed partial mixed rations with (PMR+C) and without (PMR–C) canola meal. In spring (early lactation), 32 Holstein–Friesian dairy cows were offered two amounts of the two supplement treatments in a two × two factorial arrangement of treatments for 24 days. Amounts of supplement were low (8 kg DM/cow.day) versus high (14 kg DM/cow.day). The PMR–C ration comprised wheat grain (59.5%, DM basis), maize grain (18.9%) and lucerne hay (21.6%). The PMR+C ration was the same, except some wheat grain was substituted with canola meal (21.6%). Both rations were isoenergetic, with a grain to forage ratio of 78 : 22 (DM basis). All cows were offered a low pasture allowance of 10 kg DM/cow.day to ground level. Replacing some wheat in a ration with canola meal increased pasture and total eating time. Dry matter intake did not differ between PMR–C and PMR+C cows. The present experiment also demonstrated that altering the amount of supplement did not influence the increase in eating time that occurred as a result of the inclusion of canola meal. Increasing the amount of supplement reduced pasture intake as a result of a reduction in grazing time and grazing intensity.

Partitioning of dietary nitrogen in response to feeding cereal grain supplements to dairy cows during four periods of an extended lactation

Holstein–Friesian dairy cows managed in pasture-based systems are capable of lactating for considerably longer than the traditional 300 days. However, the partitioning of dietary nutrients in the second 300 days of an extended lactation has been shown to be different from that in the first 300 days. The partitioning of dietary nitrogen (N) was investigated using two groups of eight Holstein cows in four experimental periods of 6 days, at 110, 270, 450 and 560 days in milk (DIM). During each period, cows were housed in individual stalls where N intake and output were measured. Cows in a control group received a forage-based diet ad libitum, whereas cows in a second group received 5 kg DM of cereal grain and the basal forage diet ad libitum. N intake was positively related to outputs of milk N, urinary N and faecal N, and negatively to N-use efficiency (NUE). DIM was positively related to output of urinary N and negatively related to NUE and outputs of milk N and faecal N. The partitioning of N in the second year of an extended lactation was different from that in the first year, meaning that the partitioning of N reported for cows up to 300 DIM cannot be used to accurately predict the partitioning of N in cows beyond 300 DIM. Adding grain to the diet increased total nitrogen intake but decreased NUE. However, it is plausible for the addition of cereal grain to the diet of dairy cows to increase NUE, but only when the concentration of dietary crude protein decreases and any increase in dry-matter intake is small, such that total nitrogen intake is decreased.

Rumen degradability characteristics of five starch-based concentrate supplements used on Australian dairy farms

This experiment compared the rumen degradability characteristics of five starch-based concentrate supplements used by Western Australia (WA) dairy producers. Six rumen-fistulated, non-lactating, Holstein-Friesian cows were used to measure the in sacco rumen degradability of maize grain, oats, wheat, sodium hydroxide-treated wheat (NaOH wheat) and Maximize® (a commercial pellet commonly used by WA dairy producers). Cows were offered a basal diet of custom-made cubes (60 : 40 lucerne hay : wheat grain) at maintenance feeding level. Rumen disappearance of dry matter (DM), starch and crude protein was determined for each concentrate at 0, 1, 2, 4, 8, 16, 24, 36, 48 and 72 h, and fitted to an exponential model to estimate degradation kinetics. Effective degradability coefficients were then calculated at three rumen solid-outflow rates (0.02, 0.05 and 0.08/h). Degradability of DM at 0.08/h was lowest (P < 0.001) in maize grain (0.64) and oats (0.68) and greatest in wheat (0.83), with that in NaOH wheat (0.80) and Maximize (0.76) being intermediate. Starch degradability at 0.08/h was also lowest (P < 0.001) in maize grain (0.70), intermediate for NaOH wheat (0.83) and Maximize (0.87), and greatest for wheat (0.96) and oats (0.98). Degradability of crude protein was lowest (P = 0.001) in Maximize (0.66) and NaOH wheat (0.69), greatest in oats (0.85), with that in maize grain (0.72) and wheat (0.79) being intermediate. For producers where availability of maize grain for dairy cow rations is limited, such as in WA, these results indicated that NaOH wheat and Maximize may be considered as alternative starch sources to increase post-ruminal digestion of starch, although the magnitude of this increase will still not be as great as for maize grain.

Whole-tract digestibility and nitrogen-use efficiency of partial mixed rations with and without canola meal

Increasing the crude protein (CP) concentration of a ration fed to grazing dairy cows by adding canola meal can increase milk production. The present study investigated the effect of extra CP intake on nitrogen-use efficiency and the fate of the additional dietary nitrogen (N). Sixteen spring-calved rumen fistulated cows were housed in metabolism stalls for a 9-day period and offered one of the following four treatment diets: (1) 8 kg DM/cow.day of fresh perennial ryegrass (PRG) supplemented with 12 kg DM/cow.day of a partial mixed ration (PMR) comprising oaten hay, crushed maize and wheat grain (PMR 8); (2) 12 kg DM/cow.day of fresh-cut PRG and 12 kg DM/cow.day of PMR (PMR 12); (3) the same as for PMR 8 cows, except some wheat in the PMR was replaced with canola meal (PMR+C 8); and (4) the same as the PMR 12 cows, except some wheat in the PMR was replaced with canola meal (PMR+C 12). The PMR and the PMR+C diets were iso-energetic, but the canola meal provided extra CP. Crude protein intake was 14.4%, 14.8%, 16.8% and 17.4% DM for PMR 8, PMR 12, PMR+C 8 and PMR+C 12 respectively. The addition of canola meal increased DM intake (P < 0.05) from 20.4 to 21.6 kg/day and increased N intake (P < 0.001) from 478 to 590 g/day. Nitrogen digestibility increased (P < 0.05) from 67% to 71%, nitrogen-use efficiency decreased (P < 0.05) from 37% to 32% and urinary-N output increased (P < 0.01) from 118 to 160 g/day, indicating that the additional CP fed resulted in additional N surplus. Energy-corrected milk yield for the experimental period was 34 ± 3.1 kg/cow.day (mean ± s.d.); however, due to the low number of cows, the ability to rigorously assess the effects on milk production was limited.

Effects of pasture allowance on milk production of dairy cows offered increasing amounts of partial mixed rations in spring

Milk production was measured in Holstein–Friesian cows offered low, medium or high allowances of ryegrass pasture (15, 25 or 40 kg DM/cow.day to ground level) and receiving different amounts of supplement (6, 10, 12 or 14 kg DM/cow.day) as a partial mixed ration (PMR). The 27-day experiment was conducted in spring when cows were 45 ± 17.3 days in milk (mean ± s.d.). Two groups of six cows received each of the 12 combinations of pasture allowance and PMR amount. The PMR comprised wheat grain (38%, DM basis), maize grain (18%), lucerne hay (22%) and canola meal (22%). When 6 kg DM PMR/cow.day was offered, cows grazing the low allowance produced less milk and energy-corrected milk than did cows grazing the medium and high allowances. There was no effect of pasture allowance on production of milk or energy-corrected milk at any other amount of PMR offered. When cows were offered 14 kg DM PMR/cow.day, milk fat concentrations were lower for cows grazing the high pasture allowance than for cows grazing the medium allowance. There were no differences in milk fat concentrations between cows grazing the different pasture allowances at any other amount of PMR offered. When cows were offered 6 kg DM PMR/cow.day, cows grazing the low pasture allowance yielded less milk fat than did cows grazing the medium pasture allowance. Cows grazing the high allowance had greater concentrations and yields of milk protein than did cows grazing the low allowance at all amounts of PMR offered, while cows grazing the medium allowance yielded more milk protein at some amounts of PMR. Pasture utilisation decreased with increases in both pasture allowance and amount of PMR. These results will enable farmers to better optimise feeding systems that combine both pasture and PMR.

Variation in feeding behavior and milk production among dairy cows when supplemented with 2 amounts of mixed ration in combination with 2 amounts of pasture

Variation in feeding behavior and milk production of grazing dairy cows fed a mixed ration was measured. Experiments were conducted in spring (early lactation) and autumn (late lactation) with 48 Holstein-Friesian dairy cows. Pasture allowance (low vs. high) and amounts of supplement (low vs. high) were applied to determine the effect on variation among cows in feeding behavior and milk production. The experiments investigated 4 dietary treatments in a 2×2 factorial arrangement of treatments. Daily pasture allowances were 15kg of DM/cow per day (low) and 37kg of DM/cow per day (high; to ground level); and 12kg of DM/cow per day (low) and 31kg of DM/cow per day (high; to ground level), for the spring and autumn experiments, respectively. Supplements were offered at 6kg of DM/cow per day (low) and 14kg of DM/cow per day (high); and 6kg of DM/cow per day (low) and 12kg of DM/cow per day (high), for the spring and autumn experiments, respectively. There were 2groups of 6 cows per treatment. All treatments received a partial mixed ration, defined as a total mixed ration fed between periods of grazing that contained wheat grain, corn grain, alfalfa hay, and canola meal. The grain-to-forage ratio of the supplements was 78:22 (DM basis) in both spring and autumn. In both experiments, the pre-experimental period was 14d followed by a 10-d experimental period. The variation among cows within a group in feeding behavior was influenced by the amount of supplement but not the amount of pasture offered. The variation among cows in pasture eating time approximately doubled when the amount of supplement offered increased, indicating that to reduce the variability among cows, supplement feeding management strategies need to be considered. Increasing pasture allowance had no effect on pasture eating time although pasture intake increased as a result of increased grazing intensity compared with the low pasture allowance. However, increasing the amount of supplement in the partial mixed ration feeding system reduced pasture eating time by 51min/cow per day.

Incorporating mixed rations and formulated grain mixes into the diet of grazing cows: Effects on milk composition and coagulation properties, and the yield and quality of Cheddar cheese

Effects of different strategies for feeding supplements to grazing dairy cows on the composition and coagulation properties of milk and the subsequent yield and quality of Cheddar cheese were measured. The experiment used milk from 72 Holstein-Friesian cows, averaging 45d in milk, fed according to 1 of 3 feeding strategies: (1) cows grazed a restricted allowance of perennial ryegrass pasture [approximately 14kg of dry matter (DM)/cow per day, to ground level] supplemented with milled wheat grain fed in the milking parlor and alfalfa hay offered in the paddock (control); (2) same pasture and allowance as control, supplemented with a formulated grain mix containing wheat grain, corn grain, and canola meal fed in the parlor and alfalfa hay fed in the paddock (FGM); or (3) same pasture and allowance as control, supplemented with a partial mixed ration comprising the same formulated grain mix but mixed with alfalfa hay and presented on a feed pad after each milking (PMR). For all strategies, supplements provided the same metabolizable energy and grain:forage ratio (78:22, DM basis). Within each feeding strategy, milk was sampled from cows receiving either 8 or 16kg (DM) of supplement/cow per day. There were 2 replicated groups of 6 cows per supplement amount per dietary strategy; approximately 250L of milk was sampled from each for analyses of composition and coagulation properties and the manufacture of Cheddar cheese. The experiment had a 14-d adaptation period and a 14-d measurement period. For cows fed according to the control strategy, those fed 16kg/cow per day produced milk with lower concentrations of milk fat than cows fed 8kg/cow per day. This effect was not observed for cows fed according to the FGM and PMR strategies. Milk from cows fed 16kg of DM/cow per day according to the control strategy yielded less Cheddar cheese than milk from cows fed according to the PMR strategy, with cheese yields from FGM cows being intermediate. Amount of supplement offered had minor effects on percentages of some fatty acids. We observed few other effects of feeding strategy on milk composition, types of milk protein, milk coagulation properties, or the composition and quality of the resultant Cheddar cheese. These data show that, compared with the traditional control strategy, feeding PMR or FGM may increase milk fat concentration and the subsequent yield of Cheddar cheese without compromising cheese composition or quality.

Milk production responses to different strategies for feeding supplements to grazing dairy cows

Milk production responses of grazing cows offered supplements in different ways were measured. Holstein-Friesian cows, averaging 45 d in milk, were allocated into 8 groups of 24, with 2 groups randomly assigned to each of 4 feeding strategies. These were control: cows grazed a restricted allowance of perennial ryegrass pasture supplemented with milled wheat grain fed in the milking parlor and alfalfa hay offered in the paddock; FGM: same pasture and allowance as the control supplemented with a formulated grain mix containing wheat grain, corn grain, and canola meal fed in the parlor and alfalfa hay fed in the paddock; PMRL: same pasture and allowance as the control, supplemented with a PMR consisting of the same FGM but mixed with alfalfa hay and presented on a feed pad after each milking; and PMRH: same PMR fed in the same way as PMRL but with a higher pasture allowance. For all strategies, supplements provided the same metabolizable energy and grain:forage ratio [75:25, dry matter (DM) basis]. Each group of 24 cows was further allocated into 4 groups of 6, which were randomly assigned to receive 8, 12, 14, or 16 kg of DM supplement/cow per d. Thus, 2 replicated groups per supplement amount per dietary strategy were used. The experiment had a 14-d adaptation period and a 14-d measurement period. Pasture allowance, measured to ground level, was approximately 14 kg of DM/d for control, FGM, and PMRL cows, and 28 kg of DM/d for the PMRH cows, and was offered in addition to the supplement. Positive linear responses to increasing amounts of supplement were observed for yield of milk, energy-corrected milk, fat, and protein for cows on all 4 supplement feeding strategies. Production of energy-corrected milk was greatest for PMRH cows, intermediate for FGM and PMRL cows, and lowest for control cows. Some of these differences in milk production related to differences in intake of pasture and supplement. Milk fat concentration decreased with increasing amount of supplement for all feeding strategies, but the decline was most marked for the control cows. Milk protein concentration increased for all groups as the amount of supplement increased, but was greater for FGM, PMRL, and PMRH cows than control cows. It is concluded that when supplements are fed to grazing dairy cows, inclusion of corn grain and canola meal can increase milk production even at similar metabolizable energy intakes, and that it does not matter whether these supplements are fed as a PMR or in the parlor and paddock.

The effects on ruminal pH and serum haptoglobin after feeding a grain-based supplement to grazing dairy cows as a partial mixed ration or during milking

Ruminal pH and serum concentrations of haptoglobin (Hp) were measured in order to assess the risk of subacute ruminal acidosis (SARA) in grazing cows offered rolled wheat grain twice daily in the dairy at milking (Control group; n= 64), or as a partial mixed ration (PMR group; n= 64) on a feedpad. Cows were allocated various levels of the supplement (8, 10, 12 or 14 kg dry matter/day). Ruminal pH was measured in 16 rumen-fistulated cows (eight PMR and eight Control group cows), using indwelling pH meters, recording every 10 min for 14 days. Serum Hp was analysed in samples collected from 125 cows. No differences in ruminal pH or serum Hp concentration were found between treatment groups, or levels of feeding. It was concluded that, using ruminal pH patterns and Hp as markers of SARA at the feeding levels used in this study, there were no differences between grazing cows fed the supplement either as grain in the dairy or as a PMR fed on a feedpad.

Effects of partial mixed rations and supplement amounts on milk production and composition, ruminal fermentation, bacterial communities, and ruminal acidosis

Late-lactation Holstein cows (n=144) that were offered 15kg dry matter (DM)/cow per day of perennial ryegrass to graze were randomized into 24 groups of 6. Each group contained a fistulated cow and groups were allocated to 1 of 3 feeding strategies: (1) control (10 groups): cows were fed crushed wheat grain twice daily in the milking parlor and ryegrass silage at pasture; (2) partial mixed ration (PMR; 10 groups): PMR that was isoenergetic to the control diet and fed twice daily on a feed pad; (3) PMR+canola (4 groups): a proportion of wheat in the PMR was replaced with canola meal to produce more estimated metabolizable protein than other groups. Supplements were fed to the control and PMR cows at 8, 10, 12, 14, or 16kg of DM/d, and to the PMR+canola cows at 14 or 16kg of DM/d. The PMR-fed cows had a lower incidence of ruminal acidosis compared with controls, and ruminal acidosis increased linearly and quadratically with supplement fed. Yield of milk fat was highest in the PMR+canola cows fed 14 or 16kg of total supplement DM/d, followed by the PMR-fed cows, and was lowest in controls fed at these amounts; a similar trend was observed for milk fat percentage. Milk protein yield was higher in the PMR+canola cows fed 14 or 16kg of total supplement DM/d. Milk yield and milk protein percentage were not affected by feeding strategy. Milk, energy-corrected milk, and milk protein yields increased linearly with supplement fed, whereas milk fat percentage decreased. Ruminal butyrate and d-lactate concentrations, acetate-to-propionate ratio, (acetate + butyrate)/propionate, and pH increased in PMR-fed cows compared with controls for all supplement amounts, whereas propionate and valerate concentrations decreased. Ruminal acetate, butyrate, and ammonia concentrations, acetate-to-propionate ratio, (acetate + butyrate)/propionate, and pH linearly decreased with amounts of supplement fed. Ruminal propionate concentration linearly increased and valerate concentration linearly and quadratically increased with supplement feeding amount. The Bacteroidetes and Firmicutes were the dominant bacterial phyla identified. The Prevotellaceae, Ruminococcaceae, and Lachnospiraceae were the dominant bacterial families, regardless of feeding group, and were influenced by feeding strategy, supplement feeding amount, or both. The Veillonellaceae family decreased in relative abundance in PMR-fed cows compared with controls, and the Streptococcaeae and Lactobacillaceae families were present in only minor relative abundances, regardless of feeding group. Despite large among- and within-group variation in bacterial community composition, distinct bacterial communities occurred among feeding strategies, supplement amounts, and sample times and were associated with ruminal fermentation measures. Control cows fed 16kg of DM of total supplement per day had the most distinct ruminal bacterial community composition. Bacterial community composition was most significantly associated with supplement feeding amount and ammonia, butyrate, valerate, and propionate concentrations. Feeding supplements in a PMR reduced the incidence of ruminal acidosis and altered ruminal bacterial communities, regardless of supplement feeding amount, but did not result in increased milk measures compared with isoenergetic control diets component-fed to late-lactation cows.

Grape marc reduces methane emissions when fed to dairy cows

Grape marc (the skins, seeds, stalk, and stems remaining after grapes have been pressed to make wine) is currently a by-product used as a feed supplement by the dairy and beef industries. Grape marc contains condensed tannins and has high concentrations of crude fat; both these substances can reduce enteric methane (CH4) production when fed to ruminants. This experiment examined the effects of dietary supplementation with either dried, pelleted grape marc or ensiled grape marc on yield and composition of milk, enteric CH4 emissions, and ruminal microbiota in dairy cows. Thirty-two Holstein dairy cows in late lactation were offered 1 of 3 diets: a control (CON) diet; a diet containing dried, pelleted grape marc (DGM); and a diet containing ensiled grape marc (EGM). The diet offered to cows in the CON group contained 14.0kg of alfalfa hay dry matter (DM)/d and 4.3kg of concentrate mix DM/d. Diets offered to cows in the DGM and EGM groups contained 9.0kg of alfalfa hay DM/d, 4.3kg of concentrate mix DM/d, and 5.0kg of dried or ensiled grape marc DM/d, respectively. These diets were offered individually to cows for 18d. Individual cow feed intake and milk yield were measured daily and milk composition measured on 4d/wk. Individual cow CH4 emissions were measured by the SF6 tracer technique on 2d at the end of the experiment. Ruminal bacterial, archaeal, fungal, and protozoan communities were quantified on the last day of the experiment. Cows offered the CON, DGM, and EGM diets, ate 95, 98, and 96%, respectively, of the DM offered. The mean milk yield of cows fed the EGM diet was 12.8kg/cow per day and was less than that of cows fed either the CON diet (14.6kg/cow per day) or the DGM diet (15.4kg/cow per day). Feeding DGM and EGM diets was associated with decreased milk fat yields, lower concentrations of saturated fatty acids, and enhanced concentrations of mono- and polyunsaturated fatty acids, in particular cis-9,trans-11 linoleic acid. The mean CH4 emissions were 470, 375, and 389g of CH4/cow per day for cows fed the CON, DGM, and EGM diets, respectively. Methane yields were 26.1, 20.2, and 21.5g of CH4/kg of DMI for cows fed the CON, DGM, and EGM diets, respectively. The ruminal bacterial and archaeal communities were altered by dietary supplementation with grape marc, but ruminal fungal and protozoan communities were not. Decreases of approximately 20% in CH4 emissions and CH4 yield indicate that feeding DGM and EGM could play a role in CH4 abatement.

Feeding a partial mixed ration once a day did not increase milk production compared with feeding grain in the dairy and forage in the paddock

This experiment measured milk production responses of grazing cows offered supplements in different ways. Holstein-Friesian cows averaging 89 days in milk, were allocated into six groups of 36 (each group including three rumen-fistulated cows). Two groups were randomly assigned to each of three dietary treatments: (1) cows were offered milled barley grain twice daily at milking and pasture silage in the paddock (Control); (2) the same amounts of milled barley grain and pasture silage were fed as a partial mixed ration (PMR) once a day following morning milking (PMR1); and (3) cows were supplemented with a PMR containing milled barley grain, lucerne hay, maize silage and crushed maize grain fed once a day following morning milking (PMR2). All dietary treatments were formulated to provide the same metabolisable energy and cows were offered a restricted allowance of ~14 kg DM/cow.day (to ground level) of perennial ryegrass pasture in addition to their supplement. Each group of 36 cows was further divided into four groups of nine, each of which were offered supplements at either 6, 8, 10 and 12 kg DM/cow.day. The experiment consisted of a 14-day adaptation period and an 11-day measurement period. Cows fed PMR1 and PMR2 once a day did not show an increase in milk production compared with the traditional feeding system (Control). Presumably this was a result of asynchronous supply of nutrients to the rumen (in isoenergetic diets) compromising conditions for digestion and milk production.

Ruminal pH and whole-tract digestibility in dairy cows consuming fresh cut herbage plus concentrates and conserved forage fed either separately or as a partial mixed ration

The objective of this experiment was to compare ruminal pH and whole-tract digestibility in cows consuming fresh cut herbage plus concentrates and silage or hay fed either separately or as a partial mixed ration (PMR). Fourteen rumen-fistulated Holstein-Friesian cows that had calved in late winter were housed in metabolism stalls for 9-day experiments in spring (97 days in milk (DIM)) and autumn (237 DIM). All cows were offered 8 kg dry matter (DM)/day of fresh cut perennial ryegrass (Lolium perenne L.) herbage, provided in two equal portions after each milking. Seven cows were assigned to each of two diets: (i) Control: 8.8 kg DM/cow.day milled wheat grain in two equal portions at milking, plus 3.2 kg DM/cow.day perennial ryegrass silage, with all cows receiving the silage portion of their diet after their grain but before their fresh herbage at the afternoon milking; and (ii) PMR: 12 kg DM/cow.day of a PMR containing similar ME as the Control supplements, but comprising maize grain, maize silage, wheat grain, lucerne hay (spring) and pasture silage (autumn). Intake and faecal output was measured on 5 days during each experiment, and ruminal pH was measured every 2 h for a 24-h period. Degradability of wheat and maize grain was measured using standard in sacco techniques. In both experiments, cows fed PMR had higher ruminal fluid pH than Control cows for at least part of the day. Apparent whole-tract digestibilities of DM, organic matter, nitrogen, neutral detergent fibre and starch were greater for Control than PMR cows in spring and not different in autumn (except starch). Ruminal pH was increased by feeding a maize-based PMR but this was not associated with increased whole-tract digestibility. We conclude that the ruminal pH in the Control cows was not low enough for long enough to compromise digestion, or that there was compensatory post-ruminal digestion.

Whole-tract dry matter and nitrogen digestibility of lactating dairy cows selected for phenotypic divergence in residual feed intake

The objective of this experiment was to compare the whole-tract digestibility of dry matter (DM) and nitrogen (N) in Holstein-Friesian dairy cows selected for divergent feed conversion efficiency. The experiment used 16 primiparous Holstein–Friesian dairy cows selected based on their residual feed intake (RFI) measured as growing calves. The cows were housed in individual metabolism stalls and fed lucerne cubes ad libitum plus 6 kg DM per day of crushed wheat grain. Feed intake, milk yield, faecal and urine output were measured for 5 days. Rumen fluid was collected per os from each cow on one occasion. Milk production parameters and intakes of DM, organic matter, neutral detergent fibre, acid detergent fibre and N did not differ between RFI groups. Apparent whole-tract DM digestibility and N digestibility did not differ between RFI treatment groups. Rumen metabolites were also unaffected by RFI. In conclusion, divergence in RFI as calves was not associated with differences in whole-tract DM or N digestibility in lactating cows. Therefore, emphasis on selection for phenotypic divergence in RFI may not contribute to improved utilisation of consumed nutrients in Australian Holstein-Friesian dairy cows.

Evaluation of growth hormone response to insulin-induced hypoglycaemia in dairy cattle during a 670-day lactation

Plasma growth hormone secretion in response to insulin-induced hypoglycaemia was evaluated in cows undergoing an extended lactation. Twelve multiparous Holstein-Friesian cows that calved in late winter and were managed for a 670-day lactation by delaying mating. Four experimental periods of 40 days commenced at ~73, 217, 422 and 520 (±9.1; mean ± s.d.) days in milk (DIM) during which cows were individually offered a diet of perennial ryegrass (73 and 422 DIM) or pasture hay and pasture silage (217 and 520 DIM) supplemented with either 1 kg DM grain (CONT) or 6 kg DM grain (GRAIN). Cows were fitted with jugular catheters during the final week of each experimental period. Seven blood samples over a 24-h period were collected and an insulin tolerance test was performed on each cow using a dose of 0.12 µU insulin/kg liveweight at ~100, 250, 460 and 560 DIM. This resulted in an increase in plasma growth hormone concentration occurring at 100 DIM, an intermediate and delayed response at 250 DIM, and no response at both 460 and 560 DIM. Cows in the CONT treatment had higher basal plasma growth hormone concentrations and tended to have a greater peak growth hormone response than GRAIN cows. The growth hormone response at 100 and 250 DIM is likely a homeorhetic mechanism to support milk yield during early-mid lactation. These observations are consistent with the known actions of growth hormone to promote lipid mobilisation, hepatic glucose production and an overall state of catabolism. With further research, the insulin tolerance test may be a useful tool to identify cows with greater growth hormone secretory response and increased milk production or persistency.

Replacing wheat with canola meal in a partial mixed ration increases the milk production of cows grazing at a restricted pasture allowance in spring

Milk production responses were measured in grazing cows offered supplements in different ways. Holstein–Friesian cows averaging 70 days in milk were allocated into 20 groups of eight, each including one rumen-fistulated cow. One of three dietary treatments was then randomly assigned to each of the 20 groups. Treatments were (1) Control (8 groups), where cows were supplemented with rolled wheat grain fed twice daily in the dairy and pasture silage provided in the paddock; (2) partial mixed ration (PMR; 8 groups), where cows were offered a PMR comprising rolled wheat grain, maize grain, maize silage and lucerne hay, which was presented on a feedpad immediately after each milking; the PMR was formulated to provide the same estimated metabolisable energy intake as the Control supplements; and (3) PMR+Canola (4 groups), where cows were fed in the same way as the PMR cows, except that a proportion of the wheat in the PMR was replaced with solvent-extracted canola meal. This ration was formulated to provide the same metabolisable energy as the Control and PMR treatments, but had greater amounts of crude protein. For Control and PMR treatments, supplements were offered at 8, 10, 12 or 14 kg DM/cow.day (2 groups per amount) while for the PMR+Canola treatment supplement was offered at 12 or 14 kg DM/cow.day (2 groups per amount). In addition to their supplements, all groups grazed an allowance of ~14 kg DM/cow.day (measured to ground level) of perennial ryegrass pasture. Yields of energy-corrected milk increased linearly with increasing supplement intake, but there was no difference between Control and PMR cows. When canola meal was added to the PMR, there was an increase in energy-corrected milk at a predicted supplement intake of 13.0 kg DM/cow.day. This was associated with a greater concentration and yield of milk fat in the PMR+Canola cows. Ruminal fluid pH and DM intake from pasture were also greater in PMR+Canola cows. It is concluded that farmers feeding high amounts of supplements to grazing cows could increase milk production by carefully considering the composition and form of the supplement mix, including the inclusion of canola meal.

Effects of feeding algal meal high in docosahexaenoic acid on feed intake, milk production, and methane emissions in dairy cows

This study examined effects on milk yield and composition, milk fatty acid concentrations and methane (CH4) emissions when dairy cows were offered diets containing different amounts of algal meal. The algal meal contained 20% docosahexaenoic acid (DHA) and cows were offered either 0, 125, 250, or 375 g/cow per d of algal meal corresponding to 0, 25, 50, or 75 g of DHA/cow per d. Thirty-two Holstein cows in mid lactation were allocated to 4 treatment groups, and cows in all groups were individually offered 5.9k g of dry matter (DM) per day of concentrates [683 g/kg of cracked wheat (Triticum aestivum), 250 g/kg of cold-pressed canola, 46 g/kg of granulated dried molasses, and 21 g/kg of mineral mix] and ad libitum alfalfa (Medicago sativa) hay. The algal meal supplement was added to the concentrate allowance and was fed during the morning and afternoon milking, whereas the alfalfa hay was fed individually in pens. Cows were gradually introduced to their diets over 7d and then fed their treatment diets for a further 16d. Dry matter intake and milk yield were measured daily, and milk composition was measured on a sample representative of the daily milk yield on Thursday of each week. For the last 2d of the experiment, cows were individually housed in respiration chambers to allow measurement of CH4 emissions. Dry matter intake, milk yield and milk composition were also measured while cows were in the respiration chambers. Cows ate all their offered concentrates, but measured intake of alfalfa decreased with increasing dose of DHA by 16.2, 16.4, 15.1, and 14.3 kg of DM/d, respectively. Milk yield (22.6, 23.5, 22.6, and 22.6 kg/cow per d) was not affected by DHA dose, but milk fat concentrations (49.7, 37.8, 37.0, and 38.3g/kg) and, consequently, milk fat yields (1.08, 0.90, 0.83, and 0.85 kg/d) decreased with addition of DHA. The feeding of algal meal high in DHA was associated with substantial increases in the concentrations of DHA (0.04, 0.36, 0.60, and 0.91 g/100g of milk fatty acids) and conjugated linoleic acid C18:2 cis-9,trans-11 (0.36, 1.09, 1.79, and 1.87 g/100g of milk fatty acids). Addition of DHA did not affect total emissions of CH4 (543, 563, 553, and 520 g/cow per d), nor emissions in terms of milk production (24.9, 22.1, 24.3, and 23.4 g of CH4/kg of milk), but emissions were increased with respect to total intake (22.6, 23.5, 24.5, and 24.4 g of CH4/kg of DM). These findings indicate that CH4 emissions were not reduced when dairy cows were fed a forage-based diet supplemented with DHA from algal meal.

Use of partial mixed rations in pasture-based dairying in temperate regions of Australia

There is a growing diversity and complexity of dairy farming systems in Australia. Feeding systems based on the provision of mixed rations to dairy cows grazing perennial pastures (termed partial mixed rations or PMR systems) have emerged and present the dairy industry with opportunities for improved production and feed efficiency, but also with significant challenges. Early research results are beginning to define the situations in which PMR systems are profitable and the mechanisms responsible for the improved milk responses. This review focuses on the role of PMR feeding systems in temperate dairying regions of Australia, highlights initial research findings, and identifies some of the gaps in current knowledge that warrant further research. The key findings were that, when very low allowances of pasture are offered to cows, milk production responses were driven mostly by increases in dry matter (DM) intake, and there appeared to be a minimal contribution to increased energy supply from improved whole tract DM digestibility. Differences in milk responses became apparent when >10 kg of total supplement DM was consumed (0.75 : 0.25 concentrate to forage) as PMR. There was a consistent maintenance of milk fat concentration when increasing amounts of concentrates were consumed as PMR, in contrast with supplements consumed in the dairy. There was also a consistent finding that replacing some wheat in the PMR with canola meal resulted in cows consuming more grazed pasture despite the limitations of very low pasture allowances (10–15 kg DM/cow.day, expressed to ground level). This was accompanied by further increases in energy-corrected milk yield. The potential to improve DM intake was further highlighted when pasture allowance was increased, with intake increasing from 3.6% to 4.5% of liveweight (from 20 to 25 kg DM/day for a 550-kg cow). There was also an indication that ~50% of the milk production benefit from PMR can be captured by providing the concentrate supplement as a grain mix in the dairy. There did not appear to be negative impacts of PMR systems on the social and grazing behaviour or health of cows.

Effects of different strategies for feeding supplements on milk production responses in cows grazing a restricted pasture allowance

Milk production responses of grazing cows offered supplements in different ways were measured. Holstein-Friesian cows, averaging 227 d in milk, were allocated into 6 groups of 36, with 2 groups randomly assigned to each of 3 feeding strategies: (1) cows grazed perennial ryegrass pasture supplemented with milled barley grain fed in the milking parlor and pasture silage offered in the paddock (control); (2) same pasture and allotment supplemented with the same amounts of milled barley grain and pasture silage, but presented as a mixed ration after each milking (PMR 1); and (3) same pasture and allotment, supplemented with a mixed ration of milled barley grain, alfalfa hay, corn silage, and crushed corn grain (PMR 2). For all strategies, supplements provided the same metabolizable energy and grain:forage ratio. [75:25, dry matter (DM) basis]. Each group of 36 cows was further allocated into 4 groups of 9, which were assigned to receive 6, 8, 10, or 12 kg of supplement DM/cow per day. Thus, there were 2 replicated groups per supplement amount per dietary strategy. The experiment had a 14-d adaptation period and an 11-d measurement period. Pasture allotment was approximately 14 kg of DM/d for all cows and was offered in addition to the supplement. Positive quadratic responses to increasing amounts of supplement were observed for yield of milk, energy-corrected milk (ECM), and fat and protein, and positive linear responses for concentrations of fat and protein for cows on all 3 supplement feeding strategies. No difference existed between feeding strategy groups in yield of milk, ECM, or protein at any amount of supplement offered, but yield and concentration of fat was higher in PMR 2 cows compared with control and PMR 1 cows at the highest amounts of supplementation. Responses in marginal ECM production per additional kilogram of supplement were also greater for PMR 2 than control and PMR 1 cows when large amounts of supplement were consumed. For all diets, marked daily variation occurred in ruminal fluid volatile fatty acids and pH, especially in cows fed the largest amounts of supplement. It was concluded that when supplements are fed to grazing dairy cows, a simple mix of grain and pasture silage has no benefit over traditional strategies of feeding grain in the parlor and forage in the paddock. However, yield of milk fat and marginal milk production responses can be greater if the strategy uses an isoenergetic ration that also contains alfalfa hay, corn silage, and corn grain.

Effects of wild-type, AR1 and AR37 endophyte-infected perennial ryegrass on dairy production in Victoria, Australia

A 3-year experiment compared the effects of wild-type ryegrass endophyte and two novel endophytes on milk production in dairy cattle. On three 9.9-ha farmlets in West Gippsland, Victoria, pasture swards were established that were dominant in perennial ryegrass (Lolium perenne) infected with either wild-type, AR1 or AR37 endophytes. Each farmlet was stocked with 25 spring-calving Holstein–Friesian cows, which rotationally grazed nine paddocks within their farmlet during three lactations over 3 years. The three endophytes are known to produce different alkaloids, with wild-type producing ergot alkaloids, lolitrems and peramine, AR1 producing peramine and AR37 producing epoxy-janthitrems. These alkaloids were present in fresh pasture as well as hay and silage made from that pasture. Grazed pasture comprised 53% of estimated annual DM intake. The proportion was least from December to March when the daily ration of 2 kg DM/cow.day cereal grain was increased to 6 kg/day and forage supplements were fed consisting of purchased lucerne (Medicago sativa) hay and pasture silage grown on the farmlets. There were no differences in pasture accumulation rates or nutritive characteristics of ryegrass pastures on the three farmlets and no differences in the production of milk, fat or protein by cows grazing pasture infected with the three endophytes. Ryegrass staggers was only observed in four cows consuming the wild-type-infected ryegrass in the first year when the highest concentrations of lolitrem B were recorded in pasture. Soil samples showed lower numbers of root aphids (Aploneura lentisci), mealybugs (Pseudococcidae) and pasture tunnel moths (Philobota spp.) beneath ryegrass infected with the AR37 endophyte compared with the other two endophytes. Numbers of redheaded (Adoryphorus couloni) and blackheaded (Aphodius tasmaniae) cockchafers did not differ between treatments. Under dairy management and supplementary feeding regimes common to south-eastern Australia, the novel endophytes AR1 and AR37 had no effect on the milk production compared with the wild-type endophyte, and did not cause ryegrass staggers.

Feed conversion efficiency and marginal milk production responses of pasture-fed dairy cows offered supplementary grain during an extended lactation

A study was conducted to quantify the feed conversion efficiency (FCE) and marginal milk responses of pasture-fed cows offered supplementary grain during an extended lactation of 670 days. The experiment used three groups of 10 Holstein cows in four experimental periods of 4 weeks, beginning when cows were ~60, 240, 420 and 530 days in milk (DIM). In each experimental period, cows were individually fed diets of either freshly cut perennial ryegrass pasture supplemented with triticale (60 and 420 DIM), or pasture silage and lucerne hay supplemented with wheat (240 and 530 DIM). On each occasion, one of the three groups was offered additional grain at 0.0, 2.5 or 5.0 kg DM/cow.day. Milk production was measured daily and concentrations of milk fat and protein weekly. These data were used to calculate FCE and marginal responses of milk, energy-corrected milk and milk solids (fat + protein). Results showed FCE was highest at 60 DIM and lowest at 530 DIM. Increased DM intake because of increased grain intake led to increased FCE at 240 and 530 DIM when the energy concentration of forage was lowest. Marginal milk responses were not different at any stage of lactation. For milk solids and energy-corrected milk, responses at 240 DIM were the same as at 530 DIM, but greater than at 60 DIM and 420 DIM. This study provides the first Australian data about FCE and marginal milk production responses to grain supplementation of pasture-fed cows undergoing an extended lactation. The results should provide farmers with confidence that good responses to grain can be achieved even in the latter part of a 22-month lactation.

Blood plasma concentrations of metabolic hormones and glucose during extended lactation in grazing cows or cows fed a total mixed ration

An experiment was conducted to measure the effect of diet on circulating concentrations of metabolic hormones and metabolites in cows undergoing extended lactations. Two groups of 6 Holstein-Friesian cows managed for lactations of 670 d were used in the experiment. One group was fully fed on a total mixed ration (TMR), whereas the other group grazed fresh pasture supplemented with grain (P+G). On 7 occasions between 332 and 612 d in milk, concentrations of metabolic hormones and glucose were measured in the blood plasma of each cow. Cows fed TMR gained more weight and body condition than P+G cows, but did not produce more milk during the study period. Only 3 of the TMR cows continued to lactate until 612 d in milk compared with all 6 of the P+G cows. Blood plasma from cows fed TMR had higher concentrations of glucose, insulin, glucagon, insulin-like growth factor 1, and leptin, but lower concentrations of growth hormone, than that from P+G cows. These changes were consistent with the preferential deposition of energy into adipose tissue at the expense of milk production and presumably were induced by a diet that provided precursors for gluconeogenesis that were in excess of the requirements for maintenance and prevailing milk production. The mechanism responsible for some TMR cows putting on excess weight and reducing or ceasing milk production is uncertain, but this observation has important implications for the nutritional management of cows in extended lactation programs.

Potential use of Acacia mearnsii condensed tannins to reduce methane emissions and nitrogen excretion from grazing dairy cows

We measured the effect of condensed tannins (CT) extracted from the bark of the Black Wattle tree (Acacia mearnsii) on the milk production, methane emissions, nitrogen (N) balance and energy partitioning of lactating dairy cattle. Sixty lactating cows, approximately 32 d in milk grazing ryegrass pasture supplemented with 5 kg d-1 cracked triticale grain, were allocated to three treatments: Control, Tannin 1 (163 g CT d-1) or Tannin 2 (326 g CT d-1 initially, reduced to 244 g d-1 CT by day 17). Cows were dosed twice daily after milking for 5 wk with the powdered CT extract (mixed 1:1 with water). Low and high CT supplementation reduced (P < 0.05) methane emissions by 14 and 29%, respectively (about 10 and 22% on an estimated dry matter intake basis). However, milk production was also reduced by the CT (P < 0.05), especially at the high dose rate. Milk yields were 33.0, 31.8 and 29.8 kg cow-1 d-1. Tannin 2 also caused a 19% decline in fat yield and a 7% decline in protein yield, but protein and lactose contents of milk were not affected by CT supplementation. After the initial 5-wk period, five cows representative of each treatment group were moved to metabolism facilities to determine effects of CT on energy digestion and N balance over 6 d. The energy digestibility was reduced (P < 0.05) from 76.9 (Control) to 70.9 (Tannin 1) and 66.0% (Tannin 2) and the percentage of feed N lost to urine was reduced (P < 0.05) from 39 to 26% and 22% for the respective treatments. The CT also caused a reduction (P < 0.05) in intake during the metabolism study, effectively increasing CT as a percentage of intake. Although CT can be used to reduce methane and urinary N losses from cows fed pastures with a high crude protein (CP) concentration, reduced milk yield in this study suggested the dietary concentration was too high. If CT are to be considered as a means for lowering methane emissions further research is needed to define impacts of lower doses of A. mearnsii CT on methane production and cow productivity. Dairy producers will be reluctant to adopt feeding practices that compromise profitability.Key words: Dairy cow, condensed tannins, methane, milk production, energy, nitrogen balance

Effect of type of diet and energy intake on milk production of Holstein-Friesian cows with extended lactations

The aim of this study was to measure the effect of type of diet and level of energy intake on the performance of cows undergoing extended lactations. Ninety-six Holstein-Friesian cows that calved in July and August 2004 were assigned randomly to 1 of 8 groups each of 12 cows (including 4 primiparous cows). Two of the 8 groups were assigned to each of 4 treatments that varied in lactation length (300 or 670 d) and diet (3 diets: control, high, or full total mixed ration (TMR). The 4 treatments were 1) control 300: cows were managed for a 300-d lactation and grazed pasture supplemented with grain and forage to provide a minimum daily dietary intake of 160 MJ of ME/cow; 2) control 670: as for control 300 except that cows were managed for a 670-d lactation; 3) high 670: cows were managed for a 670-d lactation and pasture was supplemented with grain and forage to provide a minimum daily dietary intake of 180 MJ of ME/cow; 4) full TMR 670: cows were managed for a TMR system that included a high body condition score at calving with cows offered a TMR during a 670-d lactation. The TMR was initially offered ad libitum indoors until about 440 DIM when the amount of TMR offered was reduced by about 2 kg of DM/d to prevent excessive weight gain. The proportions of cows still milking at the end of a 670-d lactation were similar for the control and high dietary groups. The full TMR group had fewer cows milking at 600 DIM: 17 cows milking compared with 24 cows in the control 670 group and 22 cows in the high 670 group. For the period 1 to 670 DIM, increasing the energy level in the diet (control 670 vs. high 670) resulted in a similar yield of milk and a similar fat concentration in the milk, but greater yields of milk fat and protein and greater milk protein percentage of the milk. The full TMR 670 group produced greater yields of milk and milk components (fat, protein, and lactose) and also protein percentage in the milk than the other groups. The milk solids (fat + protein) ratio for the 3 extended-lactation groups, defined as production achieved during the 24-mo calving interval divided by 2 yr (annualized production) expressed as a ratio of that produced in the normal 12-mo calving interval, was not affected by increasing the level of grain in the pasture-based diets (0.93 vs. 0.90 for control and high diets, respectively), but decreased with the TMR diet (0.79). The control 670 group produced 7.1% less milk, but only 2.4% less milk solids than the control 300 group over the 2-yr period of the study. Combining our data with that from 2 earlier studies of extended lactation demonstrated that Holstein cows with a high proportion of Northern Hemisphere genes offered pasture-based diets could achieve a high milk solids ratio, a greater proportion of cows milking at drying-off, and lower body weight gain over the lactation.

Use of monensin controlled-release capsules to reduce methane emissions and improve milk production of dairy cows offered pasture supplemented with grain

We examined the effects of monensin, provided by controlled-release capsules, on the enteric methane emissions and milk production of dairy cows receiving ryegrass pasture and grain. In a grazing experiment, 60 Holstein-Friesian cows were assigned randomly to 1 of 2 groups (control or monensin). Cows in the monensin group received 2 controlled-release capsules, with the second capsule administered 130 d after the first. Milk production was measured for 100 d following insertion of each capsule. The sulfur hexafluoride tracer gas technique was used to measure enteric methane emissions for 4 d starting on d 25 and 81 after insertion of the first capsule, and on d 83 after insertion of the second capsule. All cows grazed together as a single herd on a predominantly ryegrass sward and received 5 kg/d of grain (as-fed basis). In a second experiment, 7 pairs of lactating dairy cows (control and monensin) were used to determine the effects of monensin controlled-release capsules on methane emissions and dry matter intake. Methane emissions were measured on d 75 after capsule insertion by placing cows in respiration chambers for 3 d. Cows received fresh ryegrass pasture harvested daily and 5 kg/d of grain. The release rate of monensin from the capsules used in both experiments was 240 +/- 0.072 mg/d, determined over a 100-d period in ruminally cannulated cows. The monensin dose was calculated to be 12 to 14.5 mg/kg of dry matter intake. There was no effect of monensin on methane production in either the grazing experiment (g/d, g/kg of milk solids) or the chamber experiment (g/d, g/kg of dry matter intake). In the grazing study, there was no effect of monensin on milk yield, but monensin increased milk fat yield by 51.5 g/d and tended to increase milk protein yield by 18.5 g/d. Monensin controlled-release capsules improved the efficiency of milk production of grazing dairy cows by increasing the yield of milk solids. However, a higher dose rate of monensin may be needed to reduce methane emissions from cows grazing pasture.

Comparative Reproductive Performance and Early Lactation Productivity of Jersey × Holstein Cows in Predominantly Holstein Herds in a Pasture-Based Dairying System

The aim of this study was to compare the reproductive performance, milk production, live weight, and body condition loss during early lactation of purebred Holstein (H) cows to Jersey x H (J x H) crossbred cows in 4 Victorian herds. Cows of H and J x H breeding were managed together within each herd, and all herds had a seasonally concentrated calving pattern that commenced in early spring (July). All crossbred cows included in the study were 25, 50, or 75% H and were considered collectively as J x H regardless of the sire and dam breeds used to reach those percentages. Each herd owner provided records of reproductive performance and milk production. Compared with H cows, J x H cows had higher first-service conception rates (52 vs. 42%), higher percentages confirmed pregnant by 6 (68 vs. 54%) and 14 wk (86 vs. 78%) after the first day of inseminating, and lower final not-in-calf rates (11 vs. 16%); however, these differences were not observed in all herds. A random selection of H and J x H cows had body condition assessed on 3 occasions between the start of calving and the first day of the artificial insemination program. The selected cows were also weighed on the final occasion. Overall, body condition scores were slightly higher for J x H cows than for H cows, but changes in body condition score between calving and the start of inseminating were similar between breed groups. The H cows were 40 kg heavier than J x H cows and had daily milk yields in early lactation that were 2.2 kg higher. Daily yields of milk fat and protein did not differ between H and J x H cows during the study period. The improved reproductive performance of J x H cows compared with H cows may render them more suitable for use in dairy herds with seasonally concentrated calving patterns. Their improved reproductive performance was not associated with differences in condition loss in early lactation.

Effects of Varying Lactation Length on Milk Production Capacity of Cows in Pasture-Based Dairying Systems

The aim of this experiment was to quantify the milk production capacity of cows undergoing extended lactations while fed a pasture-based diet typical of those used in the seasonal-calving dairying systems of Victoria, Australia. One hundred twenty-five Holstein cows were randomly assigned to 1 of 5 groups. Breeding was progressively delayed after calving to enable management of the groups for lactation lengths of 10, 13, 16, 19, and 22 mo (equivalent to calving intervals of 12 to 24 mo). Cows were provided with a daily energy intake of at least 180 MJ of metabolizable energy/cow. This was supplied primarily by grazed pasture with supplementary cereal grain, pasture silage, and hay. Cows were dried off when milk volume fell below 30 kg/wk or when they reached 56 d before their expected calving date. Most cows (>96%) could lactate above this threshold for 16 mo, >80% for 19 mo, and >40% for 22 mo. There were negative relationships between lactation length and annual production of milk and milk solids (milk fat + protein), but losses were small until 16 mo. Annualized yields of milk solids were 497, 498, 495, 474, and 463 kg/cow for the 10, 13, 16, 19, and 22 mo groups, respectively. This reduction in annual production of milk solids with increasing lactation length was relatively less than for milk volume because during extended lactation, cows produced milk with higher concentrations of protein. Cows undergoing extended lactations also finished their lactations having gained more body weight and body condition than cows lactating for only 10 mo. The data showed that many cows on pasture-based diets were capable of lactating longer than the 10 mo that is standard for Victorian herds with seasonally concentrated calving patterns. Further, such extended lactations could be achieved with little penalty in terms of annual milk solids production.

Methane Emissions from Dairy Cows Measured Using the Sulfur Hexafluoride (SF6) Tracer and Chamber Techniques

Our study compared methane (CH4) emissions from lactating dairy cows measured using the sulfur hexafluoride (SF6) tracer and open-circuit respiration chamber techniques. The study was conducted using 16 lactating Holstein-Friesian cows. In each chamber, the cow was fitted with the SF6 tracer apparatus to measure total CH4 emissions, including emissions from the rectum. Fresh ryegrass pasture was harvested daily and fed ad libitum to each cow with a supplement of 5 kg of grain/d. The CH4 emissions measured using the SF6 tracer technique were similar to those using the chamber technique: 331 vs. 322 g of CH4/d per cow. The accuracy of the SF6 tracer technique was indicated by considering the ratio of the CH4 emission measured using the SF6 tracer to the emission measured using the chamber for each cow on each day. The calculated ratio of 102.3% (SE = 1.51) was not different from 100%. A higher variability within cow between days was found for the SF6 tracer technique [coefficient of variation (CV) = 6.1%] than for the chamber technique (CV = 4.3%). The variability among cows was substantially higher than within cows, and was higher for the SF6 technique (CV = 19.6%) than for the chamber technique (CV = 17.8%). Our CH4 emission data were compared with whole-animal chamber studies conducted in Canada and Ireland. In the Canadian study the SF6 technique did not measure CH4 emissions from the rectum and emissions were 8% lower than those measured using the chamber, indicating that emissions from the rectum may be greater than previously measured (1%). The relationship between CH4 emission and dry matter intake was examined for our data and for that reported in the Canadian study. There was a difference in the slopes of the regressions derived from our data and that from Canada; 17.1 vs. 20.8 g of CH4/kg of dry matter intake. A difference between the 2 locations was expected based on the difference in diet composition for these 2 studies. The SF6 tracer technique is reasonably accurate for inventory purposes and for evaluating the effects of mitigation strategies on CH4 emissions.

Modelling the bi-peak lactation curves of summer calvers in New Zealand dairy farm systems

New Zealand dairy cows traditionally calve in late winter, so their peak lactation demands are met by the increased growth of pasture in spring, and they are dried off in autumn before the decreased growth in winter. Financial premiums are offered to encourage farmers to produce milk in winter by calving cows in summer or autumn (out-of-season calving). This requires farming systems that can feed lactating cows in winter, which may include extra silages and fertilisers. The associated extra costs must be weighed against the value of the winter premium. This paper assesses the ability of Dexcel’s Whole Farm Model (WFM) to simulate out-of-season calving by comparing the model output with the observed data from an out-of-season calving trial run at Dexcel’s No. 2 dairy in Hamilton from 1998 to 2001. Trial data showed the typical lactation curve for July calvers with 1 peak in early lactation, whereas for January calvers the curve was atypical with a lower peak in early lactation and a second peak in late lactation. July and January calvers were described in the animal metabolic submodel (‘Molly’) at the start of the simulations by using observed liveweights at the beginning of the season and estimated peak daily milk yields. The management submodel used best-practice policies and the pasture submodel was driven by actual climate data. The WFM with an unmodified ‘Molly’ (without the photoperiod effect) did not predict the flatter bi-peak lactation curves of the January calvers. Driving forces responsible for the differences in the shape of lactation curves were identified and a sine function reflecting the photoperiod effect on lactation hormones was incorporated into ‘Molly’. This reduced the mean prediction error of milk yields for January calvers from 46 to 19%, and for July calvers, from 19 to 15%. The modified ‘Molly’ also showed potential to predict the atypical lactation curves of October and April calvers. After evaluating the WFM, farm systems can be simulated by altering factors such as stocking rate, fertiliser quantity and timing, and proportion of the herd calving out of season. Model output can be used for cost–benefit analysis of a wide variety of potential systems.

Endogenous Synthesis of cis-9, trans-11 Conjugated Linoleic Acid in Dairy Cows Fed Fresh Pasture

New Zealand Holstein-Friesian cows (n = 4) were used to quantify the importance of endogenous synthesis of cis-9, trans-11 conjugated linoleic acid (CLA) via Delta(9)-desaturase in cows fed a fresh pasture diet. The experiment was a 4 x 4 Latin square design with treatments arranged in a 2 x 2 factorial. Treatments lasted 4 d and were pasture only, pasture plus sterculic oil, pasture plus sunflower oil, and pasture plus sunflower oil plus sterculic oil. Abomasal infusion of sterculic oil inhibited Delta(9)-desaturase and decreased the concentration of cis-9, trans-11 CLA in milk fat by 70%. Using the changes in cis-9 10:1, cis-9 12:1 and cis-9 14:1 to correct for incomplete inhibition of Delta(9)-desaturase, a minimum estimate of 91% of cis-9, trans-11 CLA in milk fat was produced endogenously in cows fed fresh pasture. Dietary supplementation of a pasture diet with sunflower oil increased the proportion of long chain fatty acids in milk fat; however, the increase in vaccenic acid concentration was small (18%) and there was no increase in cis-9, trans-11 CLA concentration. Overall, results show that endogenous synthesis is responsible for more than 91% of the cis-9, trans-11 CLA secreted in milk fat of cows fed fresh pasture. However, the failure of plant oil supplements to increase the concentration of cis-9, trans-11 CLA in milk fat from pasture-fed cows requires further investigation.

Effects of abomasal infusion of conjugated linoleic acid on milk fat concentration and yield from pasture-fed dairy cows

The aim of this study was to investigate the effects of conjugated linoleic acid supplementation on the synthesis of milk fat in pasture-fed Friesian cows. In four cows, a commercial mixture containing 62.3% (wt/vol) conjugated linoleic acid was infused intraabomasally to avoid rumen fermentation and biohydrogenation. The design was a 4 x 4 Latin square in which each cow received infusions of 0, 20, 40, and 80 g/d of conjugated linoleic acid mixture for 4 d. Cows were fed freshly cut ryegrass/white clover pasture ad libitum. Milk fat concentration was decreased by 36, 43, and 62% and milk fat yield was decreased by 32, 36, and 60% by the 20, 40, and 80 g of conjugated linoleic acid/d treatments. Dry matter intake, milk protein concentration, and protein yield were unaffected by treatments; however, milk yield was increased by 11% during the 40-g conjugated linoleic acid/d treatment. The effects of conjugated linoleic acid infusion were most pronounced in reducing de novo fatty acid synthesis and desaturation. Results show that the inhibitory effect of this conjugated linoleic acid mixture on milk fat synthesis occurs in pasture-fed cows, and demonstrate the potential to dramatically alter gross milk composition. This technology could offer a management tool to manipulate milk composition and energy demands of pasture-fed cows.

Effects of pasture allowance on the yield and composition of milk from cows of different beta-lactoglobulin phenotypes

The objective of this study was to determine whether the differences in the composition of milk from cows of different beta-lactoglobulin beta-LG) phenotypes are affected by the amount of pasture available and, hence, pasture dry matter intake. Twenty-two Friesian cows of each of the AA and BB variants of the beta-LG phenotype were subjected to ad libitum grazing or restricted grazing in crossover experiments during spring (early lactation, approximately 60 d in milk) and summer (mid to late lactation, approximately 180 d in milk). Milk samples were collected from each cow at the end of each 8-d treatment period and analyzed for composition. Cows of the AA variant of the beta-LG phenotype had higher concentrations of whey protein and beta-LG, but lower concentrations of casein (CN), alpha-CN, kappa-CN (summer only), and BSA, than cows of the BB variant. Compared with cows with a restricted allowance, cows grazing ad libitum had higher milk yields and concentrations of protein, casein, whey protein, and all individual proteins except BSA and immunoglobulin. There were no interactions between effects of pasture allowance and phenotype on milk yield or composition. The data show that having adequate pasture for grazing cows is important not only to maximize milk yield, but also to optimize concentrations of protein and casein, and hence the manufacturing potential of milk. Further, the differences in composition of milk from cows of differing beta-LG phenotypes persisted during short-term restrictions in pasture allowance, and between spring and summer.

Milk whey protein concentration and mRNA associated with beta-lactoglobulin phenotype

Two common genetic variants of β-lactoglobulin (β-lg), A and B, exist as co- dominant alleles in dairy cattle (Aschaffenburg, 1968). Numerous studies have shown that cows homozygous for β-lg A have more β-lg and less α-lactalbumin (α-la) and casein in their milk than cows expressing only the B variant of β-lg (Ng-Kwai-Hang et al. 1987; Graml et al. 1989; Hill, 1993; Hill et al. 1995, 1997). These differences have a significant impact on the processing characteristics of the milk. For instance, the moisture-adjusted yield of Cheddar cheese is up to 10% higher using milk from cows of the β-lg BB phenotype compared with milk from cows expressing only the A variant (Hill et al. 1997). All these studies, however, describe compositional differences associated with β-lg phenotype in established lactation only. No information is available on the first few weeks of lactation, when there are marked changes in the concentrations of β-lg and α-la (Pérez et al. 1990).

Nutritional influences on the composition of milk from cows of different protein phenotypes in New Zealand

The objective of this study was to investigate the effects of contrasting nutritional regimens on milk composition from cows of different protein phenotypes. Twenty sets of seasonally calving identical twin cows that constituted five different protein phenotypes (four sets of twins per phenotype) were subjected to two nutritional treatments in crossover experiments during spring (early lactation) and summer (mid to late lactation). The phenotypes studied allowed a comparison of the AA, AB, and BB variants of both beta-lactoglobulin (beta-LG) and kappa-casein. Nutritional treatments were 1) ad libitum grazing (i.e., cows were allocated a pasture allowance of approximately 40 kg of dry matter/d per cow) plus 5 kg of a concentrate based on barley and 2) restricted grazing (pasture allowance of 20 kg of dry matter/d per cow). Milk samples were collected from each cow near the end of each 14-d treatment period and were analyzed for a detailed range of individual protein and fat constituents. Diet had significant effects on the concentrations of all milk components measured. Protein phenotype affected some protein components but not fat components. Interactions between the effects of beta-LG phenotype and diet were noted for the concentrations of some milk components. Diet and protein phenotype have important effects on the manufacturing potential of milk produced under the dairying systems of New Zealand, which rely heavily on grazing. The effects of nutrition on milk composition may depend on the beta-LG phenotype.

Seasonal and lactational influences on bovine milk composition in New Zealand

This study was designed to evaluate the respective influences of stage of lactation (SOL) and time of year on the seasonal variation in milk composition for pasture-fed dairy cows in New Zealand. Four herds of approximately 20 Friesian cows were used, one herd calving in a 6 week period beginning in each of January, April, July and October. Cows grazed rye-grass-white clover pasture only, except during June when all cows received supplementary pasture silage. Milk samples were collected from each cow in milk on four occasions during the year (September, December, March and June), to give a total of three samples per cow (early, mid and late lactation; about 30, 120 and 210 d respectively after calving). Samples were analysed for a detailed range of components. Concentrations of many milk components (e.g. total protein, fat, casein and whey protein) increased as lactation progressed; the extent of these increases depended on the time of year. These results indicated that spreading calving throughout the year would lessen seasonal variations in the gross composition of mill supplied to factories, leading to a more even distribution of product yield across the year. Despite this, variations in some important manufacturing properties were affected by time of year but not by SOL. Ratios of protein: fat and casein: whey protein were not significantly affected by SOL, but were affected by time of year. The solid fat content of milk was also affected by time of year. Seasonal variations in the manufacturing properties of milk may be reduced but not eliminated by changing the time of calving.

Effects of white clover content in the diet on herbage intake, milk production and milk composition of New Zealand dairy cows housed indoors

The effect of the proportion of clover in the diet (200, 500 or 800 g/kg total dry matter (DM) on milk production of cows housed indoors and fed on a mixture of perennial rye-grass and white clover was measured in mid (Expt I) and late (Expt II) lactation. Higher clover contents increased the nutritive value of the diets, resulting in increased energy and protein intakes. DM intakes of cows offered 500 or 800 g clover/kg DM diets ad lib. (Expt I and Expt II, Period 1) were not significantly different but were 11-17% greater (P < 0.05) than intakes of cows fed on 200 g clover/kg total DM diets. Cows offered restricted allowances (Expt II, Period 2) had similar intakes irrespective of diet. In Expt I cows fed on 500 or 800 g clover/kg DM diets ad lib. produced 30 or 33% respectively more milk (P < 0.05) than cows fed on 200 g clover/kg total DM diets. During Expt II, Period 1, cows fed on 500 or 800 g clover/kg DM diets ad lib. produced 18 or 16% more milk (P < 0.05) respectively than cows given 200 g clover/kg total DM diets. In both these experiments the increased milk yields were due to increased intake and the higher nutritive value of the high clover diets. There was no difference in the feed conversion efficiencies of cows if maintenance energy requirements were taken into account. However, cows on restricted allowances (Expt II, Period 2) showed no significant difference in milk yield, indicating that the effect of increased nutritive value was very slight. There were no consistent effects on milk fat, protein or lactose concentrations. Concentrations of blood and milk urea increased as the clover content of the diet increased (Expt 1 only), and this was associated with increased milk non-protein N and a decreased ratio of casein N: total N. Both trials indicated an optimum clover content in the diet for milk production of 600-700 g/kg total DM.

Effect of somatic cell count and stage of lactation on the quality and storage life of ultra high temperature milk

The effects of bulk milk cell count (BMCC) and stage of lactation on the quality and storage characteristics of UHT milk were investigated. The UHT milk was manufactured in a pilot plant using milk of low BMCC from early and late lactation, and milk of high BMCC from early and late lactation. Upon storage at 20 degrees C, early lactation UHT milk gelled far ahead of late lactation milk. Within each stage of lactation, high BMCC milk tended to gel first. Few differences in the organoleptic properties of the UHT milks were observed. It was apparent that the onset of age gelation may not always be related directly to the level of proteolysis, and that other factors influencing milk composition and the reactions between milk components may play more important roles. At a particular stage of lactation, proteolysis induced by mastitis may hasten the onset of gelation.