Energy and nitrogen utilization of high versus low producing dairy cows

Effects of colostrum management on transfer of passive immunity and the potential role of colostral bioactive components on neonatal calf development and metabolism

Neonatal dairy and beef calves are required to ingest adequate volumes of high-quality colostrum during their first hours of life to acquire transfer of passive immunity (TPI). As such, immunoglobulin G (IgG) has largely been the focus of colostrum research over recent decades. Yet, little is known about the additional bioactive compounds in colostrum that potentially influence newborn calf development and metabolism. The purpose of this narrative review is to synthesize research regarding the effects of colostrum management practices on TPI, as well as to address the potential role of additional colostral bioactive molecules, including oligosaccharides, fatty acids, insulin, and insulin-like growth factor-I, in promoting calf development and metabolism. Due to the importance of IgG in ensuring calf immunity and health, we review past research describing the process of colostrogenesis and dam factors influencing the concentrations of IgG in an effort to maximize TPI. We also address the transfer of additional bioactive compounds in colostrum and prepartum management and dam factors that influence their concentrations. Finally, we highlight key areas of future research for the scientific community to pursue to ultimately improve the health and welfare of neonatal dairy calves.

Factors that affect heat production in lactating Jersey cows

Heat production (HP) represents a major energy cost in lactating dairy cows. Better understanding of factors that affect HP will improve our understanding of energy metabolism. Our objective was to derive models to explain variation in HP of lactating Jersey cows. Individual animal-period data from 9 studies (n = 293) were used. The data set included cows with a wide range (min to max) in days in milk (44-410) and milk yield (7.8-43.0 kg/d). Diets included corn silage as the predominate forage source, but diets varied (min to max on DM basis) in crude protein (CP; 15.2-19.5%), neutral detergent fiber (NDF; 35.5-43.0%), starch (16.2-31.1%), and crude fat (2.2 to 6.4%) contents. Average HP was (mean ± standard deviation) 22.1 ± 2.86 Mcal/d, or 28.1 ± 3.70% of gross energy intake. Eight models were fit to explain variation in HP: (1) dry matter intake (DMI; INT); (2) milk fat, protein, and lactose yield (MILKCOMP); (3) INT and milk yield (INT+MY); (4) INT and MILKCOMP/DMI (INT+MILKCOMP); (5) mass of digested NDF, CP, and starch (DIG); (6) INT and digested energy (INT+DE); (7) INT and NDF, CP, and starch digestibility (INT+DIG); or (8) INT+MILKCOMP model plus urinary N excretion (INT+MILKCOMP+UN). For all HP models, metabolic body weight was included. All models were derived via a backward elimination approach and included the random effects of study, cow, and period within block within study. The INT models adequately explained variation in HP with a nonrandom effect-adjusted concordance correlation coefficient of 0.84. Similar adjusted concordance correlation coefficients (0.79-0.85) were observed for other HP models. The HP associated with milk protein yield and supply of digestible protein was greater than other milk production and nutrient digestibility variables. The HP associated with urinary N excretion was 5.32. Overall, HP can be adequately predicted from metabolic body weight and DMI. Milk component yield, nutrient digestibility, or urinary N excretion explained similar variation as DMI. Coefficients for milk protein and protein digestion suggest that digestion and metabolism of protein and synthesis of milk protein contribute substantially to HP of a dairy cow.

Impact of Extended Lactation on Fatty Acid Profile and Milk Composition of Dual Purpose Tropical Goat

BACKGROUND AND OBJECTIVE

Extended lactation has been implemented to increase milk yield in limited case. There is need further investigation in term of milk composition, fatty acid profile and milk flavour as recommendation for further implementation.

MATERIALS AND METHODS

The study lasted from July-September, 2017, used thirty lactating Etawah Crossbred goats in small farms of Sleman, Yogyakarta. Samples were collected from normal period and extended lactation which lasted for 2-3 months and longer than 10 months, respectively. The data on milk yield, composition, physical quality, fatty acids profile, sensory properties and nutrient consumption were measured on samples of 14 consecutive days. Assessments were done in Faculty of Animal Science and Integrated Research Laboratory, Universitas Gadjah Mada. Statistical analysis used ANOVA and Kruskal Wallis test and were processed with SPSS programme version 16.

RESULTS

Extended lactation did not affect milk yield and nutrient consumption of goat but caused higher content of milk fat, protein, total solid, acidity, caprylic, capric and total short-chain fatty acids in compared with normal lactation (p<0.05). The average values were 5.33, 4.40, 15.85, 0.30, 1.99, 9.10 and 12.13% vs. 3.75, 3.64, 13.55, 0.26, 1.69, 7.09 and 9.76% of total fatty acids in milk, respectively. Fatty acid profile did not associate with milk flavour.

CONCLUSION

Composition, acidity and short chain fatty acids content in milk of extended lactation were higher than in normal period but did not change milk flavour.

Relations of Ruminal Fermentation Parameters and Microbial Matters to Odd- and Branched-Chain Fatty Acids in Rumen Fluid of Dairy Cows at Different Milk Stages

Simple Summary

The objective of this study was to determine the relationships between milk odd- and branched-chain fatty acids (OBCFAs) and ruminal fermentation parameters, microbial populations, and base contents. Significant relationships existed between the concentrations of C11:0, iso-C15:0, anteiso-C15:0, C15:0, and anteiso-C17:0 in rumen and milk. The total OBCFA content in milk was positively related to the acetate molar proportion but negatively correlated with isoacid levels. The adenine/N ratio was negatively related to milk OBCFA content but positively associated with the iso-C15:0/iso-C17:0 ratio.

Abstract

The purpose of this research was to evaluate whether relationships exist between odd- and branched-chain fatty acids (OBCFAs) originating from milk fat and the corresponding data of ruminal fermentation parameters, microbial populations, and base contents that were used to mark microbial protein in rumen. Nine lactating Holstein dairy cows with similar body weights and parity were selected in this study, and the samples of rumen and milk were collected at the early, middle, and late stages, respectively. The rumen and milk samples were collected over three consecutive days from each cow, and the ruminal and milk OBCFA profiles, ruminal fermentation parameters, bacterial populations, and base contents were measured. The results showed that the concentrations of OBCFAs, with the exception of C11:0 and C15:0, were significantly different between milk and rumen (p < 0.05). The concentrations of anteiso-fatty acids in milk were higher than those in rumen, and the contents of linear odd-chain fatty acids were higher than those of branched-chain fatty acids in both milk and rumen. Significant relationships that existed between the concentrations of C11:0, iso-C15:0, anteiso-C15:0, C15:0, and anteiso-C17:0 in rumen and milk (p < 0.05). The total OBCFA content in milk was positively related to the acetate molar proportion but negatively correlated with isoacid contents (p < 0.05). The populations of Ruminococcus albus, R. flavefacients, and Eubacterium ruminantium were significantly related to milk C13:0 contents (p < 0.05). The adenine/N ratio was negatively related to milk OBCFA content (p < 0.05) but positively associated with the iso-C15:0/iso-C17:0 ratio (p < 0.05). Milk OBCFAs were significantly correlated with ruminal fermentation parameters, ruminal bacterial populations, and base contents. Milk OBCFAs had the potential to predict microbial nitrogen flow, and the prediction equations for ruminal microbial nitrogen flow were established for OBCFAs in dairy milk.

Negative effects of long-term feeding of high-grain diets to lactating goats on milk fat production and composition by regulating gene expression and DNA methylation in the mammary gland

Background

It is well known that feeding a high concentrate (HC) diet to lactating ruminants likely induces subacute ruminal acidosis (SARA) and leads to a decrease in milk fat production. However, the effects of feeding a HC diet for long periods on milk fatty acids composition and the mechanism behind the decline of milk fat still remains poorly understood. The aim of this study was to investigate the impact of feeding a HC diet to lactating dairy goats on milk fat yield and fatty acids composition with an emphasis on the mechanisms underlying the milk fat depression. Seventeen mid-lactating dairy goats were randomly allocated to three groups. The control treatment was fed a low-concentrate diet (35% concentrate, n = 5, LC) and there were two high-concentrate treatments (65% concentrate, HC), one fed a high concentrate diet for a long period (19 wks, n = 7, HL); one fed a high concentrate diet for a short period of time (4 wk, n = 5, HS). Milk fat production and fatty acids profiles were measured. In order to investigate the mechanisms underlying the changes in milk fat production and composition, the gene expression involved in lipid metabolism and DNA methylation in the mammary gland were also analyzed.

Results

Milk production was increased by feeding the HC diet in the HS and HL groups compared with the LC diet (P < 0.01), while the percentage of milk fat was lower in the HL (P < 0.05) but not in the HS group. The total amount of saturated fatty acids (SFA) in the milk was not changed by feeding the HC diet, whereas the levels of unsaturated fatty acids (UFA) and monounsaturated fatty acids (MUFA) were markedly decreased in the HL group compared with the LC group (P < 0.05). Among these fatty acids, the concentrations of C15:0 (P < 0.01), C17:0 (P < 0.01), C17:1 (P < 0.01), C18:1n-9c (P < 0.05), C18:3n-3r (P < 0.01) and C20:0 (P < 0.01) were markedly lower in the HL group, and the concentrations of C20:0 (P < 0.05) and C18:3n-3r (P < 0.01) were lower in the HS group compared with the LC group. However, the concentrations of C18:2n-6c (P < 0.05) and C20:4n-6 (P < 0.05) in the milk fat were higher in the HS group. Real-time PCR results showed that the mRNA expression of the genes involved in milk fat production in the mammary gland was generally decreased in the HL and HS groups compared with the LC group. Among these genes, ACSL1, ACSS1 & 2, ACACA, FAS, SCD, FADS2, and SREBP1 were down-regulated in the mammary gland of the HL group (P < 0.05), and the expressions of ACSS2, ACACA, and FADS2 mRNA were markedly decreased in the HS goats compared with the LC group (P < 0.05). In contrast to the gene expression, the level of DNA methylation in the promoter regions of the ACACA and SCD genes was increased in the HL group compared with the LC group (P < 0.05). The levels of ACSL1 protein expression and FAS enzyme activity were also decreased in the mammary gland of the HL compared with the LC group (P < 0.05).

Conclusions

Long-term feeding of a HC diet to lactating goats induced milk fat depression and FAs profile shift with lower MUFAs but higher SFAs. A general down-regulation of the gene expression involved in the milk fat production and a higher DNA methylation in the mammary gland may contribute to the decrease in milk fat production in goats fed a HC diet for long time periods.

Electronic supplementary material

The online version of this article (doi:10.1186/s40104-017-0204-2) contains supplementary material, which is available to authorized users.

The relationship between milk production potential and herbage intake of grazing dairy cows

The objective of this trial was to examine the daily herbage requirement and grass dry matter intake (DMI) of dairy cows of different levels of milk production with rotational grazing and optimum grazing conditions. The daily herbage allowance (DHA) that was required was defined as the allowance that permitted the herds to graze to a post-grazing sward height (SHA) of 70 mm. Four herds of 15 primiparous Holstein-Friesian cows were assembled with similar characteristics but different milk production potentials. The herds grazed separately and were offered a DHA such that the SHA was 70 mm for all herds. The daily yield per cow, for the 4 weeks prior to the start of the experiment (PMY), was 17·4, 19·8, 21·8 and 24·3 kg milk (s.e.0·20, P < 0·001), 0·72, 0·78, 0·87 and 0·93 kg fat (s.e. 0·021, P < 0·001), 0·59, 0·66, 0·71 and 0·77 kg protein (s.e. 0·009, P < 0·001) for herds 1 to 4, respectively. The experiment began on 30 June and finished on 16 August. The swards offered were 18-day re-growths following a previous defoliation by grazing. Herbage mass pre- and post-grazing was 2143 (s.e.33·3) and 622 (s.e.18·2) kg dry matter (DM) per ha above 40 mm, respectively and were similar for the four herds. The DHA was 21·2, 21·9, 22·9 and 23·9 (s.e. 0·13, P < 0·001) kg DM per cow above 40 mm. Individual cow grass DMI was determined once during the experimental period using the alkane technique. Experimental milk yield (EMY) was 15·1, 17·4, 18·6 and 20·8 (s.e. 0·33, P < 0·001) kg per cow per day. DMI was 14·5, 15·4, 15·5 and 16·1 (s.e. 0·47, P > 0·05). Variations in DMI were best described by the relationship: DMI = 0·85 (s.e. 3·038) + 0·32 (s.e. 0·082) ✕ EMY + 0·012 (s.e. 0·0054) ✕ experimental live weight + 2·10 (s.e. 0·738) ✕ weight gain + 0·020 (s.e. 0·0085) ✕ days in milk (residual s.d. = 1·477 and r = 0·75). EMY was linked to DMI and PMY according to the expression: EMY = –0·64 (s.e. 1·532) + 0·256 (s.e. 0·0865) ✕ DMI + 0·705 (s.e. 0·0620) ✕ PMY (residual s.d. = 1·204 and r = 0·872). It is concluded that higher yielding herds require higher DHA and this is associated with higher DMI of those herds.

Feed conversion efficiency in dairy cows: Repeatability, variation in digestion and metabolism of energy and nitrogen, and ruminal methanogens

The objective was to study repeatability and sources of variation in feed conversion efficiency [FCE, milk kg/kg dry matter intake (DMI)] of lactating cows in mid to late lactation. Trials 1 and 2 used 16 cows (106 to 368 d in milk) grouped in 8 pairs of 1 high- and 1 low-FCE cow less than 16 d in milk apart. Trial 1 determined the repeatability of FCE during a 12-wk period. Trial 2 quantified the digestive and metabolic partitioning of energy and N with a 3-d total fecal and urine collection and measurement of CH4 and CO2 emission. Trial 3 studied selected ruminal methanogens in 2 pairs of cows fitted with rumen cannulas. Cows received a single diet including 28% corn silage, 27% alfalfa silage, 17% crude protein, and 28% neutral detergent fiber (dry matter basis). In trial 1, mean FCE remained repeatedly different and averaged 1.83 and 1.03 for high- and low-FCE cows, respectively. In trial 2, high-FCE cows consumed 21% more DMI, produced 98% more fat- and protein-corrected milk, excreted 42% less manure per kilogram of fat- and protein-corrected milk, but emitted the same daily amount of CH4 and CO2 compared with low-FCE cows. Percentage of gross energy intake lost in feces was higher (28.6 vs. 25.9%), but urinary (2.76 vs. 3.40%) and CH4 (5.23 vs. 6.99%) losses were lower in high- than low-FCE cows. Furthermore, high-FCE cows partitioned 15% more of gross energy intake toward net energy for maintenance, body gain, and lactation (37.5 vs. 32.6%) than low-FCE cows. Lower metabolic efficiency and greater heat loss in low-FCE cows might have been associated in part with greater energy demand for immune function related to subclinical mastitis, as somatic cell count was 3.8 fold greater in low- than high-FCE cows. As a percentage of N intake, high-FCE cows tended to have greater fecal N (32.4 vs. 30.3%) and had lower urinary N (32.2 vs. 41.7%) and greater milk N (30.3 vs. 19.1%) than low-FCE cows. In trial 3, Methanobrevibacter spp. strain AbM4 was less prevalent in ruminal content of high-FCE cows, which emitted less CH4 per unit of DMI and per unit of neutral detergent fiber digested than low-FCE cows. Thus lower digestive efficiency was more than compensated by greater metabolic efficiencies in high- compared with low-FCE cows. There was not a single factor, but rather a series of mechanisms involved in the observed differences in efficiency of energy utilization of the lactating cows in this study.

The influence of genetic index for milk production on the response to complete diet feeding and the utilization of energy and nitrogen

Thirty-six Holstein/Friesian cows were used in a 3 × 2 factorial design randomized-block experiment to evaluate the production and nutrient utilization responses of animals of three genetic indices (cow genetic index 90 (CGI); 950, 650 and 550), each given either a complete diet (CD) or concentrate separate from grass silage through out-ofparlour feeders (OPF). The experiment included days 11 to 160 of lactation. On the CD treatment the diet was offered ad libitum with a concentrate proportion of 0.64 (dry matter (DM) basis), while on the OPF treatment the grass silage urns offered ad libitum and the allowance of concentrate was made equal to the mean concentrate intake of the CD treatment during the previous week. The concentrate was based on barley, maize gluten, molassed sugar-beet pulp, citrus pulp, soya-bean meal, fish meal and protected fat. During the experiment eight blocks each of six animals were used in metabolism studies to determine total ration digestibility, nitrogen balance and energy utilization.

No significant feeding method × genetic index interactions were found in terms of food intake, milk production or nutrient utilization. Although CGI had no significant effect on total DM intake, silage DM intake increased linearly as the cow CGI increased (P < 0.01) across the CD and OPF treatments. The high CGI cows produced respectively 6.60 and 8.25 kg/day more milk fP < 0.001) than the medium and low CGI animals without altering milk concentrations of fat and protein, but with on average a negative live-weight change with the high CGI cows. Although nitrogen digestibility was significantly higher with the low than medium CGI cows (P < 0.05), cow CGI had no significant effects on DM and energy digestibilities, daily methane energy output, heat production or the efficiency of utilization of metabolizable energy for lactation fk,) in the metabolism study. The results indicated that higher milk production with the high CGI cows was mainly attributed to an alteration in nutrient partitioning between milk energy and body energy retention.

Across the three genetic indices, feeding method had no significant effect on total DM intake, although silage DM intake was 0.46 kg/day higher (P < 0-05) on the OPF treatment. However feeding the complete diet resulted in 3.04 kg/day more milk CP < 0.05) than feeding concentrate separate from silage without altering milk concentrations of fat and protein. In the nutrient metabolism study whole tract digestibilities of DM (F < 0.001), nitrogen (P < 0.05) and energy (P < 0.01) were higher on the OPF treatment, but methane energy output and heat production were similar between the two treatments.

Dietary energy source in dairy cows in early lactation: metabolites and metabolic hormones

Negative energy balance-related metabolic disorders suggest that the balance between available lipogenic and glucogenic nutrients is important. The objectives of this study were to compare the effects of a glucogenic or a lipogenic diet on liver triacylglycerides (TAG), metabolites, and metabolic hormones in dairy cows in early lactation and to relate metabolite concentrations to the determined energy retention in body mass (ER). Sixteen dairy cows were fed either a lipogenic or glucogenic diet from wk 3 prepartum to wk 9 postpartum (pp) and were housed in climate respiration chambers from wk 2 to 9 pp. Diets were isocaloric (net energy basis). Postpartum, cows fed a lipogenic diet tended to have higher nonesterified fatty acid concentration (NEFA; 0.46 +/- 0.04 vs. 0.37 +/- 0.04 mmol/L) and lower insulin concentration (4.0 +/- 0.5 vs. 5.5 +/- 0.6 microIU/mL). No difference was found in plasma glucose, beta-hydroxybutyrate, insulin-like growth factor-I, and thyroid hormones. Liver TAG was equal between both diets in wk -2 and 2 pp. In wk 4 pp cows fed the glucogenic diet had numerically lower TAG levels, although there was no significant dietary effect. Negative relationships were detected between ER and milk fat and between ER and NEFA. A positive relationship was detected between ER and insulin concentration. Overall, results suggest that insulin plays a regulating role in altering energy partitioning between milk and body tissue. Feeding lactating dairy cows a glucogenic diet decreased mobilization of body fat compared with a lipogenic diet. The relative abundance of lipogenic nutrients, when feeding a more lipogenic diet, is related to more secretion of lipogenic nutrients in milk, lower plasma insulin, and higher plasma NEFA concentration.

Effects of Dairy Cow Genotype with Two Planes of Nutrition on Energy Partitioning Between Milk and Body Tissue

The data used in the present study were derived from a 2 (genotype) x 2 (plane of nutrition) factorial design production study using Holstein-Friesian (n = 32) and Norwegian (n = 32) first-lactation dairy cattle offered grass silage-based diets from 1 to 44 wk of lactation. The high nutrition diet had concentrate inclusions (g/kg of dry matter) of 600, 500, and 400 for lactation days of < 101, 101 to 200, and > 200, respectively, and the low nutrition diet included concentrates at 300, 200, and 100 for the same periods. Dietary metabolizable energy (ME) concentrations were measured in calorimetric chambers at lactation d 80, 160, and 240 respectively, and then applied to production data to calculate ME intake. From wk 1 to 44 of lactation, Holstein-Friesian cows had a consistently lower accumulated live weight gain and body condition score, and a consistently higher ME intake and milk energy output than Norwegian cows, irrespective of the plane of nutrition. Compared with Norwegian cows using mean data derived from the 2 planes of nutrition, Holstein-Friesian cows produced a significantly higher proportion of milk energy output over ME intake in early and mid lactation, although this increase was not significant in late lactation. In contrast, Holstein-Friesian cows partitioned a significantly lower proportion of ME intake into body tissue than Norwegian cows in early lactation, although the differences were not significant in mid or late lactation. When ME intake and energy used for maintenance, milk, and body tissue were taken into account, the efficiency of ME use for lactation was similar between the 2 genotypes offered the high or low concentrate diet during the whole lactation. It is concluded that Holstein-Friesian cows can produce more milk energy than Norwegian cows, mainly as a result of higher ME intake and because of a greater ability to partition more energy into milk and less into body tissue. The effect on energy partitioning mainly occurs in early and midlactation and is particularly evident with high concentrate diets.

Effect of selection for milk yield and dietary energy on yield traits, bovine somatotropin, and plasma urea nitrogen in dairy cows

Effects of genetic merit on energy intake, milk yield, fat and protein percentages, BW, BW change, plasma concentration of bST, and plasma concentration of urea N were determined for 139 heifers. Heifers, daughters of bulls of high genetic merit (average +408 kg of PTA for milk) or of average genetic merit (average -153 kg of PTA for milk), were allotted to either a high or low energy diet. Heifers of high genetic merit yielded 8.1% more milk and had 7.7% higher bST concentration than did heifers of average genetic merit, which were 3% heavier than heifers of high genetic merit. There was no significant effect of genetic merit group on energy intake, plasma concentration of urea N, or percentages of fat and protein. Heifers fed the high energy diet consumed 35.1% more energy, yielded 11.8% more milk with a lower fat percentage, and weighed 3% more than did heifers fed the low energy diet. The high energy diet depressed bST concentration by 13.3% and plasma concentration of urea N by 14.2% compared with concentrations for heifers fed the low energy diet. Correlations among bST, BW, and energy intake were negative and significant. Correlations of bST concentration with milk yield, fat percentage, and protein percentage were not significant. Body weight, BW change, milk yield, and energy intake were negatively correlated with plasma concentration of urea N.

Feed and animal factors influencing milk fat composition

Genetic selection for increased milk fat percentage leads to increased proportions of short-chain fatty acids in milk fat and decreased proportions of long-chain fatty acids. Milk fat composition is strongly influenced by stage of lactation; proportion of short chains (de novo synthesis) is low initially and increases until at least 8 to 10 wk into lactation. Milk fat composition is changed more by the amount and composition of dietary fat than any other dietary component. Seasonal and regional differences in milk fat composition are measurable, most likely because of local differences in feed supplies. Milk fat composition can be modified readily by changing the feeding regimen. The most significant changes in milk fat quality relate to rheological (melting) properties, which influence numerous aspects of character and quality of manufactured dairy products. Dietary fat fed to change milk fat composition may also influence contents of protein, urea, citrate, and soluble calcium in milk and influence oxidative stability and flavor. It is important for both dairy nutritionists and dairy food chemists to understand the consequences of feeding programs on milk quality.

Replacement of forage or concentrate with combinations of soyhulls, sodium bicarbonate, or fat for lactating dairy cows

A lactation study was performed from wk 4 to 19 of lactation to evaluate the ability of soyhulls with or without 1% sodium bicarbonate to replace corn silage and the ability of soyhulls, roasted soybeans, and rumen-inert fat to replace concentrate. All diets contained similar concentrations of NE(L) (tabular value), CP, and degradable protein. When forage NDF was reduced to 62.5% of total dietary NDF (32 to 36% NDF, depending on analytical method) with soyhulls, milk production and total tract nutrient digestibility were unaffected. Addition of sodium bicarbonate to the soyhull diet reduced milk production, but other production aspects were similar. As evaluated using body condition scoring, cows fed soyhulls with buffer appeared to lose less condition before the trial and to recondition earlier and more during the trial than did those fed soyhulls without buffer, which explains differences in milk production. Buffer did not increase digestibility of OM and NDF, perhaps because the high rate of passage of soyhulls limited digestibility more than did ruminal pH. Replacement of concentrate with soyhulls and fat tended to increase milk and FCM production, resulting in improved efficiency of milk production. However, fat fed to cows reduced the percentage of milk protein. As evaluated during the last 4 wk of a 6-wk posttreatment period, fat fed to cows had no residual effects on any production aspect measured.

Body composition of dairy cows according to lactation stage, somatotropin treatment, and concentrate supplementation

Body weight, condition score, deuteriated water dilution space, estimated body lipids and proteins, and calculated energy and protein balances were determined in 24 multiparous Holstein cows at wk 1, 7, 20, and 39 after parturition. Cows received two levels of energy concentrate (high and low groups) from wk 3. The objective was to estimate changes in body composition as affected by stage of lactation, concentrate level, and bST administration or placebo from wk 9 in a 2 x 2 factorial design. Cows from high and low energy groups lost 25 and 35 kg of body lipids and 3.3 and .5 kg of body proteins, respectively, during the first 7 wk of lactation. During the end of the winter period (wk 8 to 20), control and bST-injected cows lost 8.5 and 21.1 kg of body lipids, respectively. During the grazing period (wk 20 to 39), bST-injected cows gained more BW (34 kg), water (36 kg), and estimated proteins (5.8 kg) and lost more condition score (-.2 units) and estimated lipids (-11.5 kg) than controls. Using data from control periods, it was calculated that 1 unit change in body condition score corresponded to changes of 35 to 44 kg in BW (corrected for estimated gut content variation), 21 to 29 kg in body lipids, and 200 to 300 Mcal in body energy. One kilogram of corrected BW change corresponded to a change of 4.3 or 5.5 to 5.9 Mcal in body energy when calculated from cumulative energy balances or body components, respectively.

Lipid nutrition

Cows in early lactation or producing more than 80 lb of milk per day need supplemental fat and can benefit from it. Fat should be added to the diet over a period of several weeks to allow the cows to become accustomed to it. Feed intake should be monitored because additional fat may decrease feed intake and offset the benefit of the fat. Supplemental fat should not exceed 4 to 5% of the dry matter intake. The first 2% of added fat should be supplied by oilseeds under most circumstances. The next 1 or 2% can come from commodity fat if availability and handling ability permits its use. If the last increment of fat is needed, it should be supplied by specialty fats that have been processed to improve ruminal inertness. Extra calcium, magnesium, and ruminally undegraded protein should be added to the diet when fat is added. Fat is a more expensive source of energy than feed grains in most of the world and should not be used beyond needs.

Dietary fat, protein degradability, and calving season: effects on nutrient use and performance of early lactation cows

Twelve multiparous Holstein cows calving in fall and 12 calving in summer were blocked into four groups and used in a 2 x 2 x 2 factorial to determine the effects of season of calving, dietary fat, and protein degradability on milk production and efficiency of NEL utilization in a 16-wk study. Blocks were assigned randomly to one of four dietary treatment combinations: 1) control concentrate plus soybean meal (high degradability protein supplement); 2) control concentrate plus a mixture of heated soybean meal and corn gluten meal (low degradability protein supplement); 3) a blend of the control concentrate and a concentrate containing 12.1% fat to provide 1 kg d-1 fat, plus soybean meal; and 4) concentrate as in diet 3 plus heated soybean meal and corn gluten meal. Nutrient intake, milk yield and composition, BW changes, and daily ambient temperature were monitored. Intake of DM appeared to be related to NDF intake but was not affected by fat, protein degradability, or calving season. Intake of NEL was increased by feeding fat. Digestabilities of DM and CP were increased and fiber was decreased by feeding fat. Percentage and yields of milk fat, SNF, and protein and 4% FCM production were higher in cows calving in fall. Milk fat percentage was low in all cows in the study. Efficiency of energy utilization for milk production was decreased in cows fed fat and calving in the summer and by low protein degradability during wk 5 to 8 of lactation. At high concentrate intake, calving season had more effect on milk production than level of fat or protein degradability.