Timing of supplementation alters grazing behavior and milk production response in dairy cows

Influence of amount and frequency of protein supplementation to steers consuming low-quality, cool-season forage: intake, nutrient digestibility, and ruminal fermentation

This experiment evaluated the influence of protein supplementation frequency (SF) and amount offered on intake, nutrient digestibility, and ruminal fermentation by rumen-fistulated beef steers consuming low-quality [2.9% crude protein (CP); dry matter (DM) basis], cool-season forage. Seven Angus × Hereford steers (300 ± 27 kg) fitted with ruminal cannulas were randomly assigned to 1 of 7 treatments in an incomplete 7 × 4 Latin square. Treatments, in a 2 × 3 factorial design plus a non-supplemented control (CON), consisted of 2 levels of supplemental soybean meal, 100% (F) or 50% (H) of the estimated rumen-degradable protein requirement, provided daily (D), once every 5 d (5D), or once every 10 d (10D). Experimental periods were 30 d and dry matter intake (DMI) was measured from days 19 to 28. On days 21 (all supplements provided) and 30 (only daily supplements provided; day immediately prior to supplementation for 5D and 10D treatments) ruminal fluid was collected for ruminal pH, ammonia-N (NH3), volatile fatty acids (VFA), and determination of ruminal fermentation variables. Forage and total DM, organic matter (OM), and nitrogen (N) intake increased with supplementation (P ≤ 0.04). However, a linear effect of SF × amount of supplement interaction was observed for forage and total DM, OM, and N intake (P ≤ 0.04), with each variable decreasing as SF decreased, but the decrease being greater with F vs. H. Apparent total tract DM, OM, and neutral detergent fiber digestibility was not affected by supplementation or amount of supplement provided (P ≥ 0.10). In contrast, N digestibility increased with supplementation and for F vs. H (P < 0.01). Digestibility of DM, OM, and N increased linearly as SF decreased (P ≤ 0.03). When all supplements were provided, ruminal NH3, total VFA, and molar proportions of all individual VFA increased with supplementation (P ≤ 0.04), whereas acetate:propionate ratio decreased (P < 0.01). When only daily supplements were provided, none of the aforementioned fermentation parameters were affected (P ≥ 0.09). In summary, reducing the amount of supplemental CP provided to ruminants consuming low-quality forages, when supplementation intervals are >5 d, can be a management tool to maintain acceptable levels of DMI, nutrient digestibility, and ruminal fermentation while reducing supplementation cost.

Effect of protein supplementation on yield and milk composition of F1 Holstein x Zebu cows kept in deferred pasture of brachiaria grass

ABSTRACT The objective of this study was to evaluate different supplementation strategies concentrated to F1 Holstein x Zebu lactating cows managed in deferred signal grass pasture on the yield and composition of milk and body weight gain. Thirty six F1 Holstein x Zebu cows with an average lactation period of 267 ± 10 days, mean body weight of 548 ± 19kg were used following a completely randomized design in a 4 x 5 factorial scheme, being four feeding strategies and five days under evaluation. The treatments consisted of four nutritional strategies: deferred pasture as a source of roughage without supplementation (PDSS); deferred pasture as a source of roughage with protein supplement offer (PDCS); deferred pasture supplemented with 15 kilos of corn silage (natural base) + 1,200 grams of protein supplement (PDSP) and corn silage (ad libitum) + 700 grams of protein supplement (SMP). There was no interaction (P> 0.05) between the nutritional plans and days under evaluation for any of the variables. It was found that cows fed SMP showed milk production 26.06% higher than the other nutritional plans (mean of 11.46kg/day). F1 Holstein/Zebu cows handled in deferred pasture in a traditional way supplemented with protein maintains milk yield.

Integrating Plantain (Plantago lanceolata L.) and Italian Ryegrass (Lolium multiflorum Lam.) into New Zealand Grazing Dairy System: The Effect on Farm Productivity, Profitability, and Nitrogen Losses

A two-year farm system study was conducted at Canterbury, New Zealand to evaluate the effects on farm productivity, profitability, and nitrogen (N) losses of integrating plantain (Plantago lanceolate L.) and Italian ryegrass (Lolium multiflorum Lam.) into a ryegrass and white clover (RGWC)-based dairy system. Three farm systems were compared: (1) a lower input RGWC-based system (LIRG) with stocking rate of 3.5 cow/ha, annual N fertiliser rate of 150 kg/ha, and imported feed level of <1.2 t DM/cow/year; (2) a lower input ryegrass + plantain-based system (LIRG + PL) with a stocking rate of 3.5 cow/ha, annual N fertiliser rate of 150 kg/ha, and imported feed level of <1.2 t DM/cow/year; and (3) a higher input RGWC-based system (HIRG) with a stocking rate of 5.0 cow/ha, annual N fertiliser rate of 300 kg/ha, and imported feed level of >1.2 t DM/cow/year. Cows in the LIRG + PL system grazed a diverse mix of Italian ryegrass, perennial ryegrass, white clover, and plantain (60% of farmlet area), and a mixed sward of plantain-white clover (40% of farmlet area). The average annual herbage harvested was similar between LIRG + PL and LIRG (11.7 t DM/ha), but greater in HIRG (12.7 t DM/ha) with the increased N fertiliser rate. During the calving to dry-off period, the average imported supplement feed per ha was higher in HIRG (8.0 t DM) compared with LIRG (3.2 t DM) and LIRG + PL (3.7 t DM). Average milk solid production (MS; fat + protein) was similar in LIRG + PL (1640 kg/ha) and LIRG (1622 kg/ha), but greater in HIRG (2130 kg/ha). Estimated profitability (NZD/ha) at milk price of NZD 6.5/kg MS was 10% greater for HIRG than LIRG + PL and LIRG, and similar (<1.5% numerical difference) between LIRG + PL and LIRG. The average estimated annual N leaching loss from the LIRG and LIRG + PL was 31% and 56% less than the loss from the HIRG. These large reductions in N leaching loss were achieved without a large decrease in profitability (i.e., LIRG and LIRG + PL compared to HIRG). In addition, the estimated reduction in N losses from the LIRG + PL system compared to LIRG suggests that an Italian ryegrass + plantain-based dairy system is a viable strategy to reduce the environmental footprint while maintaining farm profitability. However, the environmental benefits of plantain and Italian ryegrass estimated in this study require further confirmation through direct measurements at full farm level.

Time of Grain Supplementation and Social Dominance Modify Feeding Behavior of Heifers in Rotational Grazing Systems

Social hierarchy affects the access of animals to feed resources. On daily rotational pasture systems, supplementation time may influence feeding behavior. This trial was designed to test the effect of grain delivery time on the feeding behavior of heifers. Heifers divided into two groups according to breed (n = 15 Braford and n = 19 Jersey) were tested in a crossover design with two treatments: INITIAL—supplement at 8 am (entry time to a fresh paddock), and MIDDLE—supplement at 4 pm (middle time of paddock use). Animals entered a new paddock every morning, and grain supplement at 2 kg/animal/day was offered at the fence line (1 m/animal). Then, ingestive and other behaviors were registered by direct visual observation through scan sampling at 2-min intervals for 1 h after grain supply. Agonistic interactions were recorded continuously (instigator–victim) to build a social matrix whereby each heifer was defined as dominant, intermediate, or subordinate. Weekly pasture samples were collected according to the order that animals left the feeding area, using the hand-plucking technique, to determine crude protein and fiber content. Heifers spent more time grazing on the INITIAL treatment (p < 0.0001) but exhibited more behaviors on the MIDDLE treatment (p < 0.0001). Dominant heifers spent more time eating grain (p = 0.0008), whereas subordinate heifers spent more time grazing along the paddock (p = 0.0067), but not along the fence (p = 0.0008). The crude protein content of pasture samples was higher for the INITIAL treatment (p < 0.0001). Behavioral interaction occurred with respect to the order of leaving the feeding area, social rank, and crude protein consumed (p = 0.04). Subordinate heifers consistently grazed more and ate less grain supplement than dominant and intermediate heifers. However, when grain supplement was offered at the time animals entered the paddock, more grazing activity took place during supplement feeding, and subordinate heifers could select a high-protein diet. In the INITIAL treatment, this means that subordinate animals could benefit from the better pasture available, keeping a distance from dominant heifers, reducing agonistic interactions and likely improving their welfare.

Diurnal Concentration of Urinary Nitrogen and Rumen Ammonia Are Modified by Timing and Mass of Herbage Allocation

Simple Summary

Low nitrogen use efficiency in grazing dairy cows leads to high urinary N excretion, which contributes to greenhouse gases emission. This problem has been associated with high N and low energy intake, increasing rumen ammonia (NH₃) concentration, and thereby, increasing urinary N excretion. Under this situation, it is important to discover nutritional and grazing management strategies that allow reduced urine N excretion in the pasture. This study evaluated whether changes in time of herbage allocation and herbage mass modify the diurnal pattern of urinary nitrogen (N) concentration and ruminal NH₃ of lactating dairy cows. We found that the combination of time of herbage allocation and herbage mass modified rumen NH₃ production and urinary N concentration. Results suggest that maintaining cows in the holding pen at the milking parlor for two hours after morning and afternoon milking could allow collection of urine from cows in the slurry pit during peak N concentration, returning cows to the pasture at a time of day when urinary N concentration is decreased.

Abstract

The objective of this work was to evaluate whether changes in time of herbage allocation and herbage mass (HM) (low (L) or medium (M)) modify the diurnal pattern of urinary nitrogen (N) concentration and ruminal ammonia (NH₃) of lactating dairy cows. Four Holstein-Friesian cows fitted with rumen cannula were randomly allocated to one of four treatments: 1) low herbage mass in the morning (L-AM) (Access to new herbage allocation after morning milking with a herbage mass (HM) of 2000 kg DM/ha); 2) low herbage mass in the afternoon (L-PM) (Access to new herbage allocation after afternoon milking with a HM of 2000 kg DM/ha); 3) medium herbage mass in the morning (M-AM) (Access to new herbage allocation after morning milking with a HM of 3000 kg DM/ha); and 4) medium herbage mass in the afternoon (M-PM) (Access to new herbage allocation after afternoon milking with a HM of 3000 kg DM/ha). A four by four Latin Square design with four treatments, four cows, and four experimental periods was used to evaluate treatment effects. Rumen NH₃ concentration was greater for L-AM compared to L-PM and M-PM at 13:00 and 16:00 h. Urine urea and N concentrations were lower for M-AM compared to L-AM. Urine N concentration was greater for L-AM than other treatments at 10:00 hours and greater for M-PM compared to M-AM at 16:00 hours. Results suggest that maintaining the cows in the holding pen at the milking parlor for two hours after morning grass silage supplementation for L-AM and for two hours after afternoon grass silage supplementation for M-PM, could allow collection of urine from cows at the holding pen and storage of urine in the slurry pit during the time of peak N concentration, returning cows to the pasture at a time of day when urinary N concentration is decreased.

The Order of Grass and Maize Silage Supplementation Modifies Milk Yield, Grazing Behavior and Nitrogen Partitioning of Lactating Dairy Cows

The aim of this study was to evaluate the effects of the order of grass silage (GS) and maize silage (MS) supplementation on milk yield, grazing behavior and nitrogen (N) partitioning of lactating dairy cows during autumn. Thirty-six Holstein-Friesian dairy cows were randomly assigned to one of three treatments, and cows remained on these treatments for a 62 days period: (1) MIX; cows supplemented with 3 kg of dry matter (DM) of silage containing 1.5 kg DM of MS and 1.5 kg DM of GS in both the morning and afternoon; (2) GS-MS; cows supplemented with 3 kg DM of GS in the morning and 3 kg DM of MS in the afternoon; (3) MS-GS; cows supplemented with 3 kg DM of MS in the morning and 3 kg DM of GS in the afternoon. All cows received a pasture allowance of 17 kg DM/cow/d and 3 kg DM of concentrate. Grazing time and pasture intake were unaffected by treatment; however, milk production was greater for MS-GS, while milk protein was greater for GS-MS. Urinary N excretion was greater for MS-GS than MIX. In conclusion, MS-GS resulted in high milk yield but also high urinary N excretion, while MIX resulted in low urinary N excretion but also decreased milk yield.

The assessment of supplementation requirements of grazing ruminants using nutrition models

This paper was aimed to summarize known concepts needed to comprehend the intricate interface between the ruminant animal and the pasture when predicting animal performance, acknowledge current efforts in the mathematical modeling domain of grazing ruminants, and highlight current thinking and technologies that can guide the development of advanced mathematical modeling tools for grazing ruminants. The scientific knowledge of factors that affect intake of ruminants is broad and rich, and decision-support tools (DST) for modeling energy expenditure and feed intake of grazing animals abound in the literature but the adequate predictability of forage intake is still lacking, remaining a major challenge that has been deceiving at times. Despite the mathematical advancements in translating experimental research of grazing ruminants into DST, numerous shortages have been identified in current models designed to predict intake of forages by grazing ruminants. Many of which are mechanistic models that rely heavily on preceding mathematical constructions that were developed to predict energy and nutrient requirements and feed intake of confined animals. The data collection of grazing (forage selection, grazing behavior, pasture growth/regrowth, pasture quality) and animal (nutrient digestion and absorption, volatile fatty acids production and profile, energy requirement) components remains a critical bottleneck for adequate modeling of forage intake by ruminants. An unresolved question that has impeded DST is how to assess the quantity and quality, ideally simultaneously, of pasture forages given that ruminant animals can be selective. The inadequate assessment of quantity and quality has been a hindrance in assessing energy expenditure of grazing animals for physical activities such as walking, grazing, and forage selection of grazing animals. The advancement of sensors might provide some insights that will likely enhance our understanding and assist in determining key variables that control forage intake and animal activity. Sensors might provide additional insights to improve the quantification of individual animal variation as the sensor data are collected on each subject over time. As a group of scientists, however, despite many obstacles in animal and forage science research, we have thrived, and progress has been made. The scientific community may need to change the angle of which the problem has been attacked, and focus more on holistic approaches.

How does stage of lactation and breeding worth affect milk solids production and production efficiency of grazing dairy cows?

The study investigated the effect of stage of lactation and Breeding Worth (BW) index on estimated dry matter intake (DMI), milk solids (MS) production, energy use efficiency (EUE) and feed conversion efficiency (FCE) of grazing cows. Two hundred crossbred cows with similar calving date (14 August ± 9.97 days), live weight (471.5 ± 44.02) and age (7.5 ± 1.25 years) were separated into five groups (n = 40) based on New Zealand BW index: Low BW (BW = 63.1); Medium Low BW (BW = 88.2); Medium BW (BW = 19.1); Medium High BW (BW = 128.9); and High BW (BW = 146.9). Milk samples were collected in early, mid and late lactation and herbage samples were taken the day before milk sampling. The DMI was estimated by back-calculation based on metabolizable energy requirement for maintenance and production. The MS production, herbage DMI, EUE and FCE declined from early to late lactation. The overall results suggest regardless of the stage of lactation, cows with higher BW had a higher DMI, MS production and FCE.

Effect of timing of corn silage supplementation to Holstein dairy cows given limited daily access to pasture: intake and performance

The timing in which supplements are provided in grazing systems can affect dry matter (DM) intake and productive performance. The objective of this study was to evaluate the effect of timing of corn silage supplementation on ingestive behaviour, DM intake, milk yield and composition in grazing dairy cows. In total, 33 Holstein dairy cows in a randomized block design grazed on a second-year mixed grass-legume pasture from 0900 to 1500 h and received 2.7 kg of a commercial supplement at each milking. Paddock sizes were adjusted to provide a daily herbage allowance of 15 kg DM/cow determined at ground level. The three treatments imposed each provided 3.8 kg DM/day of corn silage offered in a single meal at 0800 h (Treatment AM), equally distributed in two meals 0800 and 1700 h (Treatment AM-PM) or a single meal at 1700 h (Treatment PM). The experiment was carried out during the late autumn and early winter period, with 1 week of adaptation and 6 weeks of measurements. There were no differences between treatments in milk yield, but 4% fat-corrected milk yield tended to be greater in AM-PM than in AM cows, which did not differ from PM (23.7, 25.3 and 24.6±0.84 kg/day for AM, AM-PM and PM, respectively). Fat percentage and yield were greater for AM-PM than for AM cows and intermediate for PM cows (3.89 v. 3.66±0.072% and 1.00 v. 0.92±0.035 kg/day, respectively). Offering corn silage in two meals had an effect on herbage DM intake which was greater for AM-PM than AM cows and was intermediate in PM cows (8.5, 11.0 and 10.3±0.68 kg/day for AM, AM-PM and PM, respectively). During the 6-h period at pasture, the overall proportion of observations on which cows were grazing tended to be different between treatments and a clear grazing pattern along the grazing session (1-h observation period) was identified. During the time at pasture, the proportion of observations during which cows ruminated was positively correlated with the DM intake of corn silage immediately before turn out to pasture. The treatment effects on herbage DM intake did not sufficiently explain differences in productive performance. This suggests that the timing of the corn silage supplementation affected rumen kinetics and likewise the appearance of hunger and satiety signals as indicated by observed changes in temporal patterns of grazing and ruminating activities.

A farm-scale framework to assess potential farm- and regional-scale implications of removing palm-kernel expeller as a supplementary feed for dairy cows

Farm-scale models were integrated with spatially discrete estimates of pasture production to examine the potential farm and regional implications of removing palm-kernel expeller (PKE) as a supplementary feed from dairy farms in Southland, New Zealand. The following two farm-production systems representing the majority of dairy farms in the region were modelled: a System 3 farm (D3; mid-intensification, with 10–20% of imported feed) and a System 4 farm (D4; mid- to high intensification, with 20–30% of imported feed). Within each system, the impact of the following four PKE options was explored: (1) a control with PKE (Baseline); (2) no PKE, with fewer cows producing the same amount of milk per cow as in Baseline; (3) no PKE, with the same number of cows producing less milk per cow than in Baseline; and (4) PKE replaced with barley grain. Barley grain provides for similar flexibility (timing of purchase and feeding), and can be sourced locally. Faced with the need to remove PKE as a dietary ingredient, farmers would benefit from adopting the second PKE option (no PKE, with fewer cows producing the same amount of milk per cow as in Baseline); farm-operating profits were reduced by only 3% (compared with 30% of System 4 farms adopting the third PKE option, i.e. no PKE, with the same number of cows producing less milk per cow than in Baseline) relative to the Baseline farms. The narrow range of mean annual nitrate-nitrogen (nitrate-N) leaching losses (estimates ranged from 30 to 33 kg N/ha) reflects similar estimates of N intake and N excreted in urine across the modelled options. Substantial amounts of barley grain would need to be transported into the region or produced locally to replace PKE.

Effect of time of maize silage supplementation on herbage intake, milk production, and nitrogen excretion of grazing dairy cows

The objective of this study was to evaluate the effect of feeding maize silage at different times before a short grazing bout on dry matter (DM) intake, milk production, and N excretion of dairy cows. Thirty-six Friesian × Jersey crossbred lactating dairy cows were blocked in 9groups of 4 cows by milk solids (sum of protein and fat) production (1.26±0.25kg/d), body weight (466±65kg), body condition score (4±0.48), and days in milk (197±15). Groups were then randomly assigned to 1 of 3 replicates of 3 treatments: control; herbage only, supplemented with 3kg of DM/cow of maize silage after morning milking approximately 9h before pasture allocation (9BH); and supplemented with 3kg of DM/cow of maize silage before afternoon milking approximately 2h before pasture allocation (2BH). Herbage allowance (above the ground level) was 22kg of DM/cow per day for all groups of cows. Cows were allocated to pasture from 1530 to 2030 h. Maize silage DM intake did not differ between treatments, averaging 3kg of DM/cow per day. Herbage DM intake was greater for control than 2BH and 9BH, and greater for 9BH than 2BH (11.1, 10.1, and 10.9kg of DM/cow per day for control, 2BH, and 9BH, respectively). The substitution rate (kilograms of herbage DM per kilograms of maize silage DM) was greater for 2BH (0.47) than 9BH (0.19). Milk solids production was similar between treatments (overall mean 1.2kg/cow per day). Body weight loss tended to be less for supplemented than control cows (-0.95, -0.44, and -0.58kg/cow per day for control, 2BH, and 9BH, respectively). Nitrogen concentration in urine was not affected by supplementation or time of supplementation, but estimated urinary N excretion tended to be greater for control than supplemented cows when urinary N excretion estimated using plasma or milk urea N. At the time of herbage meal, nonesterified fatty acid concentration was greater for control than supplemented cows and greater for 9BH than 2BH (0.58, 0.14, and 0.26mmol/L for control, 2BH, and 9BH, respectively). Timing of maize silage supplementation relative to a short and intensive herbage meal can reduce the substitution rate and increase herbage DM intake of grazing dairy cows.

Effect of timing and type of supplementary grain on herbage intake, nitrogen utilization and milk production in dairy cows grazed on perennial ryegrass pasture from evening to morning

The present study aimed to clarify the effect of timing and type of supplementary grain in grazing dairy cows on herbage dry matter intake (HDMI), nitrogen utilization and milk production. Eight lactating cows were allowed to graze from evening to morning during three seasonal periods (spring, summer, autumn). They were randomly allocated to four treatments (timing: pre- (Pre) or post-grazing (Post), for large grain allotments consisting of 75% of daily grain offered; grain type: barley or corn) in 4 × 4 Latin square designs in each period. In the spring period, HDMI was greater for cows fed corn than those fed barley (P = 0.005), whereas cows in the Pre treatment had a similar HDMI, higher (P = 0.049) urinary purine derivative concentration and greater (P = 0.004) milk yield compared with cows in the Post treatment. In the summer and autumn periods, timing treatments did not affect HDMI, nitrogen utilization or milk production, but cows supplemented with barley had higher urinary purine derivatives concentration (P < 0.05) and milk yield (P < 0.05) compared with those supplemented with corn. The results indicate that large grain allotments immediately before evening grazing during early grazing seasons increased ruminal microbial protein synthesis and milk production without reducing HDMI regardless of grain type.

Effect of increased concentrate allotment before evening grazing on herbage intake, nitrogen utilization and rumen fermentation in dairy cows grazed on perennial ryegrass pasture

Two experiments were conducted to elucidate the effect of increased concentrate allotment before evening grazing on herbage intake, nitrogen utilization and rumen fermentation in dairy cows. In experiment 1, nine lactating cows were grazed in the morning and evening sessions (2.5 h each). The cows were allocated to treatments of three concentrate allotment levels before the evening grazing session by altering proportions to daily total offered; 25%, 50% and 75%. Daily herbage dry matter intake quadratically decreased with increasing the concentrate allotment levels (P < 0.05). Nitrogen utilization was similar among treatments. To investigate diurnal changes in rumen fermentation, a second experiment was conducted where six ruminally cannulated non-lactating dairy cows grazed in the morning and evening sessions (3 h each) were subjected to the same treatments as experiment 1. Total volatile fatty acid concentration in the rumen linearly increased with increasing the concentrate allotment levels throughout the pre-evening grazing session to the post-morning grazing session (P < 0.01). The results indicate that dairy cows reduce daily herbage intake but do not alter nitrogen utilization with increasing concentrate allotment before evening grazing. © 2016 Japanese Society of Animal Science.

The effect of feeding maize silage 1 h or 9 h before the herbage meal on dry matter intake, milk production, nitrogen partitioning and rumen function of lactating dairy cows

The study was conducted to evaluate the effect of the timing of feeding maize silage before a short herbage meal on dry matter (DM) intake, milk production, nitrogen (N) partitioning and rumen function of lactating dairy cows. Ten lactating, pregnant, Friesian × Jersey rumen-fistulated dairy cows aged 4–5 years were blocked in pairs by milksolids (MS; sum of protein and fat) production (1.73 ± 0.097 kg MS/cow.day; mean ± s.d.), bodyweight (519 ± 24.7 kg), days in milk (163 ± 12.5), and body condition score (3.9 ± 0.21). Cows within pairs were randomly allocated to one of two treatments: (1) five cows were offered one-third of their estimated total DM intake (5 kg/cow.day) as maize silage after the afternoon milking at 1500 hours, ~1 h before herbage was provided (1BH); (2) five cows were offered one-third of their estimated total DM intake as maize silage after morning milking at 0700 hours, ~9 h before herbage was provided (9BH). All cows were offered two-thirds of their total estimated DM intake (11 kg/cow.day) over a period of 4 h from 1600 hours to 2000 hours as freshly cut perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens) in an indoor system. Cows were adapted to diets for 9 days (Days 1–9), followed by 5 days of measurement (Days 10–14). Maize silage DM intake did not differ between treatments averaging 5.1 kg DM/cow.day. Herbage DM intake was greater (P = 0.02) for 9BH (11.2 kg DM/cow.day) than 1BH (10.4 kg DM/cow.day). Milk yield (P = 0.001) and MS production (P = 0.08) were greater for 9BH than 1BH (18.8 vs 15.4 kg/cow.day and 1.63 vs 1.48 kg MS/cow.day, respectively). There was no effect of time of supplementation on N partitioned to milk, faeces, or urine. The purine derivatives to creatinine ratio, as an indication of microbial protein production, was greater (P = 0.04) for 9BH than 1BH. Daily mean rumen pH and the concentration of total rumen volatile fatty acids, acetate, butyrate, and ammonia N were not affected by treatment. However, the peak concentration of ruminal ammonia N was 27% lower (P < 0.05) for 9BH than 1BH. The concentration of non-esterified fatty acid (P = 0.03) and beta-hydroxy butyric acid (P = 0.01) were greater for 1BH than 9BH (0.14 vs 0.09 and 0.81 vs 0.71 mmol/L, respectively). These results indicate that under herbage feed restriction, altering the time of supplementation relative to the herbage meal can increase herbage DM intake and subsequent milk production.

Herbage intake and ruminal digestion of dairy cows grazed on perennial ryegrass pasture either in the morning or evening

This study aimed to clarify diurnal fluctuations of herbage intake, ruminal fermentation of herbage carbohydrates and proteins, and digesta particulate weight in the rumen of grazing dairy cows. Six ruminally cannulated, non-lactating dairy cows were grazed on perennial ryegrass/white clover pasture either in the morning (04.00 to 08.00 hours) or the evening (16.00 to 20.00 hours). Cows grazed in the evening spent more time (P < 0.01) and consumed more herbage (P < 0.01) compared with cows grazed in the morning. Higher (P < 0.05) daily mean concentrations of total volatile fatty acid, propionate and n-butyrate in rumen fluid were observed for cows grazed in the evening compared with cows grazed in the morning. Although cows grazed in the evening ingested more crude protein compared with cows grazed in the morning, no significant difference in NH3 -N concentration in rumen fluid was observed between them. The ratio of purine-derivative concentration to creatinine concentrations was higher (P < 0.01) in the urine of cows grazed in the evening than in cows grazed in the morning. These results clearly indicated that evening grazing was advantageous for dairy cows compared with morning grazing, in terms of ruminal fermentable energy intake and nitrogen utilization efficiency.

Invited review: An evaluation of the likely effects of individualized feeding of concentrate supplements to pasture-based dairy cows

In pasture-based dairy systems, supplementary feeds are used to increase dry matter intake and milk production. Historically, supplementation involved the provision of the same amount of feed (usually a grain-based concentrate feed) to each cow in the herd during milking (i.e., flat-rate feeding). The increasing availability of computerized feeding and milk monitoring technology in milking parlors, however, has led to increased interest in the potential benefits of feeding individual cows (i.e., individualized or differential feeding) different amounts and types of supplements according to one or more parameters (e.g., breeding value for milk yield, current milk yield, days in milk, body condition score, reproduction status, parity). In this review, we consider the likely benefits of individualized supplementary feeding strategies for pasture-based dairy cows fed supplements in the bail during milking. A unique feature of our review compared with earlier publications is the focus on individualized feeding strategies under practical grazing management. Previous reviews focused primarily on research undertaken in situations where cows were offered ad libitum forage, whereas we consider the likely benefits of individualized supplementary feeding strategies under rotational grazing management, wherein pasture is often restricted to all or part of a herd. The review provides compelling evidence that between-cow differences in response to concentrate supplements support the concept of individualized supplementary feeding.

Limitations and potential for individualised feeding of concentrate supplements to grazing dairy cows

The increasing availability and installation of computerised feeding and milk-monitoring technology in Australia and New Zealand has led to an increased interest in feeding individual cows different amounts and types of supplements over lactation. However, there is confusion about the potential benefits of individualised feeding strategies compared with feeding the same amount of supplement to all cows in the herd on any given day. The majority of bail feeding research conducted over the past 30 years has identified little difference in cow response between flat-rate feeding and more complicated approaches of split feeding or feeding to individual cow milk yield. However, it must be noted that many of these experiments involved animals with ad libitum access to a forage supply. This is an important distinction as individual cows receiving high-quality forage ad libitum would be able to compensate, at least partially, for any shortage in concentrate. Large variability in response to supplements among individual cows within the herd implies that there should be a benefit from individualised bail feeding practices. This review examines the potential for individualised bail feeding in pasture-based dairy systems, considering both system (pasture allowance and type) and cow-level parameters (e.g. dry matter intake, milk yield, genotype, bodyweight, stage of lactation) that could affect the individual cow response to a particular supplement, and discusses the current limitations and future challenges for implementing this technology on farm. Recommendations for future research are made to address any knowledge gaps.

Carbohydrate supplements and their effects on pasture dry matter intake, feeding behavior, and blood factors associated with intake regulation

Supplementary feeds are offered to grazing dairy cows to increase dry matter (DM) and metabolizable energy (ME) intakes; however, offering feed supplements reduces pasture DM intake, a phenomenon known as substitution. The objective of the study was to investigate changes in blood factors associated with intake regulation in monogastric species in pasture-fed dairy cows supplemented with either a starch- or nonforage fiber-based concentrate. Fifteen multiparous Friesian × Jersey cross cows were assigned to 1 of 3 treatments at calving. Measurements were undertaken in wk 8 of lactation. Treatments were pasture only, pasture plus a starch-based concentrate (3.5 kg of DM/cow per day; STA), and pasture plus a nonforage fiber-based concentrate (4.4 kg of DM/cow per day). Pelleted concentrates were fed at an isoenergetic rate in 2 equal portions at a.m. and p.m. milkings. Measurements were undertaken to investigate differences in pasture DM intake, feeding behavior, and profiles of blood factors for 4h after a.m. and p.m. milkings, the periods of intensive feeding in grazing cows. Supplementing cows with STA concentrate reduced pasture DM intake to a greater extent than the fiber concentrate, although time spent eating did not differ between treatments. The blood factor response to feeding differed between the a.m. and p.m. feeding events. Blood factors associated with a preprandial or fasted state were elevated prefeeding in the a.m. and declined following feeding, whereas satiety factors increased. In comparison, the blood factor response to feeding in the p.m. differed, with responses to feeding delayed for most factors. Plasma ghrelin concentration increased during the p.m. feeding event, despite the consumption of feed and the positive energy state remaining from the previous a.m. feeding, indicating that environmental factors (e.g., sunset) supersede physiological cues in regulating feeding behavior. The greater reduction in pasture DM intake for the STA treatment in the p.m. may be related to the level of hunger or satiety before the feeding event and not solely to the consumption of supplement. Data indicate that neuroendocrine factors are, at least in part, responsible for the substitution of pasture for supplementary feeds.