Effects of supplementation of dairy cattle with fish oil on silage intake, milk yield and milk composition

The effects of level of fish oil inclusion in the diet on grass silage intake, and milk yield and composition of dairy cows offered either 5 or 10 kg concentrates/d were evaluated in a ten treatment, partly balanced, changeover design experiment involving 50 cows in early lactation. Concentrates were prepared to provide 0, 150, 300 or 450 g fish oil/cow per d or 300 g fish oil/cow per d from a premix when each animal was offered 5 kg/d. The fish oil was predominantly from herring and mackerel caught in the North Atlantic while the fish oil premix was obtained from a commercial source and used palm kernel expeller as a carrier. Increasing fish oil supplementation decreased silage dry matter intake and the concentrations of milk fat and protein, and increased milk yield and diet digestibility. There were significant interactions between concentrate feed level and level of fish oil for silage intake and milk yield. Other than for the concentrations of milk fat and protein, and 20:4n-6 fatty acids, the source of fish oil did not affect forage intake or animal performance. Fish oil supplementation also decreased the concentrations of milk protein by 0.9 g/kg for each 100 g increase in fish oil supplementation, the depression being similar at each level of concentrate feeding. Supplementing the feed of dairy cows with 450 g fish oil/cow per d decreased the concentration of milk fat by 15 g/kg. This study also showed that feeding dairy cattle with fish oil is an efficient method of increasing eicosapentaenoic acid in the human diet through transfer into milk.     

发酵黄芪粉对奶牛产奶量及乳成分的影响研究

研究发酵黄芪粉对奶牛产奶量及乳品质的影响.对照组奶牛饲喂基础日粮,试验Ⅰ、Ⅱ和Ⅲ组奶牛分别饲喂10、20和30 g/(头·d)的发酵黄芪粉基础日粮.结果表明:与对照组相比,试验组奶牛产奶量增加了0.95、1.45和1.58 kg/(头·d),但试验Ⅱ、Ⅲ组组间差异不显著;可显著提高奶牛乳蛋白率,但对奶牛乳脂率、乳糖及非脂固型物均无显著影响;可降低奶牛乳体细胞数,其中试验Ⅱ、Ⅲ组奶牛乳体细胞数显著低于对照组和试验Ⅰ组,但试验Ⅱ、Ⅲ组组间差异不显著;可提高奶牛经济效益,各试验组奶牛经济效益分别高于对照组2.6、3.4和2.72元/(头·d).该试验条件下,发酵黄芪粉以20 g/(头·d)的添加量较好.     

Predicting energy × protein interaction on milk yield and milk composition in dairy cows

Feed management is one of the principal levers by which the production and composition of milk by dairy cows can be modulated in the short term. The response of milk yield and milk composition to variations in either energy or protein supplies is well known. However, in practice, dietary supplies of energy and protein vary simultaneously, and their interaction is still not well understood. The objective of this trial was to determine whether energy and protein interacted in their effects on milk production and milk composition and whether the response to changes in the diets depended on the parity and potential production of cows. From the results, a model was built to predict the response of milk yield and milk composition to simultaneous variations in energy and protein supplies relative to requirements of cows. Nine treatments, defined by their energy and protein supplies, were applied to 48 cows divided into 4 homogeneous groups (primiparous or multiparous × high or low milk potential) over three 4-wk periods. The control treatment was calculated to cover the predicted requirements of the group of cows in the middle of the trial and was applied to each cow. The other 8 treatments corresponded to fixed supplies of energy and protein, higher or lower than those of the control treatment. The results highlighted a significant energy × protein interaction not only on milk yield but also on protein content and yield. The response of milk yield to energy supply was zero with a negative protein balance and increased with protein supply equal to or higher than requirements. The response of milk yield to changes in the diet was greater for cows with high production potential than for those with low production potential, and the response of milk protein content was higher for primiparous cows than for multiparous cows. The model for the response of milk yield, protein yield, and protein content obtained in this trial made it possible to predict more accurately the variations in production and composition of milk relative to the potential of the cow because of changes in diet composition. In addition, the interaction obtained was in line with a response corresponding to the more limiting of 2 factors: energy or protein.     

Effects of sodium carbonate on milk yield, milk composition, and blood components of dairy cows in early lactation

Eighteen multiparous Friesian cows were paired according to lactation number and expected calving date and assigned randomly to one of two diets in a crossover design experiment to study effects of sodium carbonate on milk yield, milk composition, blood metabolites plus Na, and K in early lactation. Diets were concentrate containing either 0 or 1.2% sodium carbonate (as fed) for ad libitum intake plus 7.0 kg of wet brewers grains and 5.5 kg of long-stemmed alfalfa hay per cow daily. Dry matter intake, milk yield, milk protein percentage and yield, and percentages of milk lactose and milk SNF were not significantly affected. Compared with the control diet, the sodium carbonate treatment increased milk fat percentage (3.98 vs. 3.53%) and yield (1.23 vs. 1.07 kg/d), 4% FCM yield (30.9 vs. 28.2 kg/d) and milk total solids (12.47 vs. 12.04%). No significant differences were observed in blood plasma concentrations of glucose, CP, urea, acetate, beta-hydroxybutyrate, triglycerides, FFA, Na, or K when sodium carbonate was added to diets for early lactation cows.     

Effects of feeding fish meal and n-3 fatty acids on milk yield and metabolic responses in early lactating dairy cows

The study was designed to test the effects of feeding fish meal (FM) and specific n-3 fatty acids on milk yield and composition, dry matter intake, plasma concentrations of metabolic hormones and metabolites, and liver triglyceride accumulation in early lactating cows. From 5 to 50 d in milk (DIM), cows were fed diets that were isonitrogenous, isoenergetic, and isolipidic containing none (control), 1.25, 2.5, or 5% menhaden FM or 2.3% Ca salts of fish oil fatty acids (CaFOFA). Milk yield (48.2, 49.8, 48.6, 53.5, and 52.2 ± 1.0 kg/d, respectively) and dry matter intake (22.7, 22.8, 23.0, 23.8, and 24.7 ± 0.5 kg/d, respectively) differed among diets. Average daily plasma glucose concentration (53.4, 55.3, 51.1, 57.6, and 57.3 ± 1.3 mg/dL, respectively) was also affected by diet, and plasma insulin concentration was increased by 5% FM and 2.3% Ca-FOFA. At 25 and 50 DIM, blood was collected before feeding and hourly for 11 h after feeding. Plasma glucose concentrations in cows during the day were similar among diets at 25 DIM, but differed at 50 DIM (54.6, 54.4, 52.4, 60.5, and 58.3 ± 1.4 mg/dL for 0, 1.25, 2.5, and 5% FM or 2.3% CaFOFA, respectively). Plasma insulin was increased in cows fed 5% FM and 2.3% CaFOFA at 25 DIM and was similar among diets at 50 DIM. Dietary treatments had no significant effect on milk composition, energy balance, or on daily plasma concentrations of nonesterified fatty acids, β-hydroxybutyrate, and urea. Plasma aspartate aminotransferase and hepatic triglyceride concentration in cows did not differ among diets at 21 DIM. Results from this experiment demonstrate that dietary supplementation with FM or n-3 polyunsaturated fatty acids in early lactating dairy cows significantly increased milk yield and DMI with no change in milk composition.     

Effects of feeding fish meal to cows on digestibility, milk production, and milk composition.

Holstein cows in early lactation, producing about 30 kg/d of milk, were fed high energy diets containing 5% Megalac. Three protein treatments, soybean meal diet (16% CP), fish meal diet (16% CP), and soybean meal-fish meal diet (20% CP) were compared in a change-over design. Digestibilities of DM, gross energy, CP, and ADF were not affected significantly by protein treatments. The fish meal diet decreased DMI but increased milk and SCM production compared with the soybean meal diet. Daily production of milk, SCM, and milk components (fat, protein, and lactose) were highest and BW gain lowest for the high protein soybean meal-fish meal diet. The fish meal and soybean meal-fish meal diets increased fat percentage but decreased lactose percentage of milk compared with soybean meal diet. This suggests that, for each diet, the energy supply was adequate, and the observed changes were the effects of protein (i.e., AA) supply to the cows. Thus, there seems to be good reason to feed a good quality undegradable protein like fish meal to cows producing more than 30 kg/d of milk.     

Effects of grass silage and soybean meal supplementation on milk production and milk fatty acid profiles of grazing dairy cows

The effects of supplementation with grass silage and replacement of some corn in the concentrate with soybean meal (SBM) on milk production, and milk fatty acid (FA) profiles were evaluated in a replicated 4 × 4 Latin square study using 16 dairy cows grazing pasture composed of ryegrass, Kentucky bluegrass, and white clover. Each experimental period lasted for 3 wk. The 4 dietary treatments were PC, 20 h of access to grazing pasture, supplemented with 6 kg/d of corn-based concentrate mixture (96% corn; C); PCSB, 20 h of access to grazing pasture, supplemented with 6 kg/d of corn- and SBM-based concentrate mixture (78% corn and 18% SBM; CSB); SC, 7 h of access to grazing pasture during the day and 13 h of ad libitum access to grass silage at night, supplemented with 6 kg/d of C concentrate; and SCSB, 7 h of access to grazing pasture during the day and 13 h of ad libitum access to grass silage at night, supplemented with 6 kg/d of CSB concentrate. The concentrate mixtures were offered twice each day in the milking parlor and were consumed completely. Grass silage supplementation reduced dietary crude protein and concentration of total sugars, and dietary SBM inclusion increased dietary crude protein concentration and decreased dietary starch concentration. Milk yield and energy-corrected milk were increased by SBM supplementation of cows with access to grass silage. Milk protein concentration was lower in cows offered grass silage, regardless of whether SBM was fed. Dietary SBM inclusion tended to increase milk fat concentration. Plasma urea N was reduced by silage feeding and increased by SBM supplementation. Supplementation with grass silage overnight could represent a useful strategy for periods of lower pasture availability. Dietary inclusion of SBM in solely grazing cows had no effects on milk production and composition, exacerbated the inefficient capture of dietary N, and increased diet cost. Grass silage supplementation affected milk FA profiles, increasing both the FA derived from de novo synthesis and those derived from rumen microbial biomass, and decreasing the sum of C18 FA (mostly derived from diet or from mobilization of adipose tissue reserves). Milk fat concentrations of conjugated linoleic acid cis-9, trans-11, vaccenic acid (18:1 trans-11), and linolenic acid (18:3n-3) were unaffected by grass silage supplementation, suggesting that partial replacement of pasture by unwilted grass silage does not compromise the dietary quality of milk fat for humans.     

Effects of sucrose supplementation on dry matter intake,milk yield,and blood metabolites of periparturient Holstein dairy cows

Thirty-four multiparous Holstein dairy cows (780 +/- 17.2 kg body weight; 3.4 +/- 0.08 body condition score) were used in a completely randomized design to evaluate the effects of fermentable carbohydrate source on dry matter (DM) intake, milk production, and blood metabolites of transition cows. Treatments were initiated 30 d before expected calving date. After calving, all cows went onto a similar lactating cow diet. Dry matter intake was measured daily, and milk production and composition were measured weekly for 56 d after calving The control diet consisted of 11.5% ground corn, whereas the treatment diet consisted of sucrose replacing 2.7% of ground corn on a DM basis. Prepartum plasma glucose concentrations were higher (66.3 vs. 69.3 +/- 1.13 mg/dl) for cows fed the diet containing sucrose. Glucose concentrations were not different postpartum. Prepartum and postpartum nonesterified fatty acids, blood urea N, and insulin did not differ between treatments. Substitution of sucrose as a readily available carbohydrate source for ground corn did not affect prepartum or postpartum DM intake. Milk yield, 3.5% fat-corrected milk yield, and milk components did not differ between treatments. Results from this research demonstrated that partially replacing ground corn with sucrose did not enhance prepartum or postpartum intake or performance.     

Effect of site and source of energy supplementation on milk yield in dairy cows

The effect of infusing similar energy equivalents of starch into the rumen, or starch or oil into the abomasum was studied in four midlactation cows in a 4 x 4 Latin square design experiment; controls were ruminally infused with water. Cows were fitted with cannulas in the rumen, abomasum, and ileum, and nutrient digestion in the rumen and small intestine was evaluated with Cr as a digesta marker. Ruminal infusions of starch, or abomasal infusions of starch or oil, were associated with a decrease in voluntary feed organic matter intake. Overall energy intake was reduced in oil-infused, but not in starch-infused cows. Nonstructural carbohydrate digestibility in the rumen and in the small intestine was similar among treatments. In abomasally infused cows 3.4 kg/d of nonstructural carbohydrates was apparently digested in the small intestine. Milk production was reduced in oil-infused cows, but the efficiency of milk energy and protein yield was unaffected by treatments. Plasma glucose, insulin, and IGF-1 concentration, mammary glucose extraction rate, rumen ammonia and plasma urea, and arterial and mammary extraction rate of amino acids were all similar among treatments. Large quantities of starch can be digested in the rumen or small intestine of dairy cows. There appear to be no metabolic advantage to increasing the supply of starch to the rumen or the abomasum of mid-lactation dairy cows maintained on highly concentrated diets and exhibiting a positive energy balance.     

Effects of particle size and formaldehyde treatment of soybean meal on milk production and composition for dairy cows

Twenty-four lactating dairy cattle were used to study the effects of formaldehyde treatment and reduction of particle size of soybean meal on milk production and composition. Cows were fed diets containing one of the following soybean meals: 1) untreated, coarse; 2) untreated, fine; 3) formaldehyde-treated, fine. Formaldehyde reduced the solubility of soybean meal protein from 22.7 to 2.9%. Grinding soybean meal reduced particle size from 842 to 249 micron. Formaldehyde treatment did not affect intake or milk production but resulted in higher efficiency of milk production (1.43 versus 1.46 kg fat-corrected milk/kg dry matter intake). Milk protein (3.08 versus 2.85%) and solids-not-fat (8.51 versus 8.35%) contents were reduced by formaldehyde. Cows fed fine soybean meal had higher dry matter intakes (22.0 versus 20.8 kg dry matter/day) and gained more body weight; however, milk production was not affected by particle size. Grinding soybean meal reduced production efficiency (1.47 versus 1.42 kg milk/kg dry matter intake) and milk fat (3.70 versus 3.33%). Lack of production response and reduced milk protein from formaldehyde treatment suggests possible overprotection of protein. Fine grinding of soybean meal appeared to favor body weight gain rather than milk production.     

Effects of glucagon infusions on protein and amino acid composition of milk from dairy cows

Changing the composition of milk proteins and AA affects the nutritional and physical properties of dairy products. Intravenous infusions of glucagon decreases milk protein production and concentration by promoting the use of gluconeogenic blood AA for hepatic glucose synthesis. Little is known about how the diversion of AA to gluconeogenesis affects the composition of milk proteins and AA. The objective was to quantify changes in composition of milk protein and AA in response to i.v. glucagon infusions. Three separate experiments were used: 1) 8 Holstein cows were fed ad libitum and infused with glucagon at 10 mg/d for 14 d, 2) 7 Holstein cows were feed restricted and infused with glucagon at 10 mg/d for 14 d, and 3) 4 Brown Swiss cows were infused with glucagon at 5 and 10 mg/d for 2 d each. Milk and milk component yields and milk protein and amino acid composition of samples, collected with blood samples at the first and last day of the glucagon infusion period, were compared with those collected 1 d before and after the glucagon infusion period. Glucagon infusions decreased milk protein production and concentration in each experiment by at least 0.2 ± 0.05 kg/d and 4 ± 0.4 g/L, respectively. The decrease was accompanied by changes in milk protein composition, the most consistent being an increase in κ-casein (1.68 ± 0.27%). Overall, glucagon infusions resulted in higher proportions of κ-casein and α_S2-casein (1.34 ± 0.51%) and smaller proportions of α_S1-casein (−3.83 ± 1.75%) and α-lactalbumin (−0.91 ± 0.32%). Glucagon had little impact on milk AA composition except an increase in glycine (0.26 ± 0.11%). The results suggest that milk protein synthesis is regulated by many factors including AA and glucose availability.     

Effects of insulin and amino acids on milk protein concentration and yield from dairy cows.

Our study investigated the effect of insulin on the regulation of milk protein synthesis in well-fed cows (n = 4) with or without additional amino acids (AA). The design was a two-way crossed factorial with two 12-d periods involving abomasal infusions of either water or a mixture of casein (500 g/d) plus branched-chain AA (88 g/d). During the last 4 d of each period a hyperinsulinemic-euglycemic clamp was performed; insulin was infused at 1.0 microgram.kg of BW-1.h-1 to increase circulating levels fourfold, and euglycemia was maintained by infusion of glucose. Cows were fed a diet formulated to exceed requirements for metabolizable energy and protein. During abomasal water infusion, the insulin clamp increased milk protein yields by 15% (+128 g/d); when combined with abomasal infusion of casein plus branched-chain AA, milk protein yield was increased by 25% (+213 g/d). These increases resulted from equivalent increases in milk protein concentration and milk yield. Concentrations of casein and whey proteins in milk were increased by insulin clamp treatments; however, there were no major changes in the relative proportions of individual casein and whey proteins. Plasma concentrations of essential AA were reduced (-33%) during the insulin clamp treatments; effects were most dramatic for the branched-chain AA (-41%) and their keto acids (-45%). Results confirm the important regulatory role of the endocrine system in milk protein synthesis and demonstrate this potential to produce milk protein is not fully expressed.     

Effects of melatonin on the yield and composition of milk from grazing dairy cows in New Zealand

The aim was to determine whether administration of melatonin would alter the yield and composition of milk from grazing dairy cows in summer. Twelve sets of spring-calving identical twin Friesian cows were used in the experiment. In late-November (late spring), one twin from each set was given slow-release melatonin implants behind the ears (108 mg melatonin/cow). Two further implantations occurred at 4-weekly intervals to maintain increased circulating concentrations of melatonin for 12 weeks. The other twin served as a control. Milk yield and composition were measured twice prior to treatment and then four times over the following 12 weeks. Concentrations of melatonin, prolactin and insulin-like growth factor 1 (IGF-1) were measured in blood plasma twice before treatment and then either seven (melatonin and prolactin) or three (IGF-1) further times during the experiment. Management procedures for all cows were similar and cows grazed a daily pasture allowance of approximately 30 kg DM/cow as their sole feed source. In melatonin-treated cows there was a decrease in mean concentrations of prolactin in plasma, but concentrations of IGF-1 did not change. Melatonin reduced milk yield by 6 weeks after treatment and by the end of the 12-week experimental period milk yield in melatonin-treated cows had fallen by 23%. Melatonin also reduced concentrations of lactose in milk, but increased concentrations of fat, protein and casein, changes that were broadly similar to those that occur in late lactation in seasonally calving dairy cows. Thus, the results suggest that some of the variation in the volume and quality of milk throughout the season in New Zealand dairy systems may be due to changes in photoperiod mediated by increased concentrations of plasma melatonin in association with decreased concentrations of plasma prolactin.     

Effects of clinical mastitis on milk yield in dairy cows.

The effect of clinical mastitis on milk yield was studied in 24,276 Finnish Ayrshire cows that calved in 1993 and were followed for one lactation (i.e., until culling or the next calving). Cows that had only mastitis, but no other diseases, and cows that had no diseases (healthy cows) during the lactation were included in the study. Monthly test day milk yields were treated as repeated measurements within an animal in a mixed model analysis. Mastitis index categories were created to relate the timing of mastitis to the test day milk measures. Statistical models (a separate model for each parity) included fixed effects of calving season, stage of lactation, and mastitis index. An autoregressive correlation structure was used to model the association among the repeated measurements. The effect of mastitis occurring at different periods during the lactation was studied. The daily loss during the first 2 wk after the occurrence of mastitis varied from 1.0 to 2.5 kg, and the total loss over the entire lactation varied from 110 to 552 kg and depended on parity and the time of mastitis occurrence. Regardless of the time of occurrence during the lactation, mastitis had a long-lasting effect on milk yield; cows with mastitis did not reach their premastitis milk yields during the remainder of the lactation after onset of the disease.     

Effects of selenium form on blood and milk selenium concentrations,milk component and milk fatty acid composition in dairy cows

BACKGROUND: Human health may be improved if milk with a favorable fatty acid composition and Se concentration is ingested. The present study is to determine how a basal diet supplemented with daily 5 mg Se as Se‐enriched yeast (SY) or sodium selenite (SS) affects the fatty acid composition and Se concentration of bovine milk. The effects of Se form on blood Se concentration, erythrocyte glutathione peroxidase 1 (GPx1) activity, serum GPx3 activity and milk yield and component were also studied. RESULTS: Both Se forms, when compared to control group, increased Se concentrations of blood (P < 0.01) and milk (P < 0.01), erythrocyte GPx1 activity (P < 0.05) and milk percentages of polyunsaturated fatty acids (PUFA) (P < 0.05) and cis‐9,cis‐12 linoleic acid (P < 0.05). Cows supplemented with SY had higher Se levels in blood (P < 0.01) and milk (P < 0.01) and percentage of PUFA in milk (P < 0.05) when compared with those supplemented with SS. Milk yield, milk component and serum GPx3 activity were not significantly affected by Se form. CONCLUSION: Supplementation of diet with SY appears to be of more benefit than SS in producing favorable milk with high PUFA and Se concentrations. Copyright © 2010 Society of Chemical Industry     

Effects of decreasing metabolizable protein and rumen-undegradable protein on milk production and composition and blood metabolites of Holstein dairy cows in early lactation

This study was conducted to evaluate the effects of decreasing dietary protein and rumen-undegradable protein (RUP) on production performance, nitrogen retention, and nutrient digestibility in high-producing Holstein cows in early lactation. Twelve multiparous Holstein lactating cows (2 lactations; 50 ± 7 d in milk; 47 kg/d of milk production) were used in a Latin square design with 4 treatments and 3 replicates (cows). Treatments 1 to 4 consisted of diets containing 18, 17.2, 16.4, and 15.6% crude protein (CP), respectively, with the 18% CP diet considered the control group. Rumen-degradable protein levels were constant across the treatments (approximately 10.9% on a dry matter basis), whereas RUP was gradually decreased. All diets were calculated to supply a postruminal Lys:Met ratio of about 3:1. Dietary CP had no significant effects on milk production or milk composition. In fact, 16.4% dietary CP compared with 18% dietary CP led to higher milk production; however, this effect was not significant. Feed intake was higher for 16.4% CP than for 18% CP (25.7 vs. 24.3 kg/d). Control cows had greater CP and RUP intakes, which resulted in higher concentrations of plasma urea nitrogen and milk urea nitrogen; cows receiving 16.4 and 15.6% CP, respectively, exhibited lower concentrations of milk urea nitrogen (15.2 and 15.1 vs. 17.3 mg/dL). The control diet had a significant effect on predicted urinary N. Higher CP digestibility was recorded for 18% CP compared with the other diets. Decreasing CP and RUP to 15.6 and 4.6% of dietary dry matter, respectively, had no negative effects on milk production or composition when the amounts of Lys and Met and the Lys:Met ratio were balanced. Furthermore, decreasing CP and RUP to 16.4 and 5.4%, respectively, increased dry matter intake.     

Effect of combinations of fish meal and feather meal on milk fatty acid content and nitrogen utilization in dairy cows

The effect of supplemental fishmeal in combination with feathermeal at two different proportions in the diet on milk docosahexaenoic acid (DHA) content was investigated. Recently, benefits to human health have been attributed to the consumption of this fatty acid, which is normally present in marine lipids. Six Holstein cows past peak lactation were used in a Latin square design with a 2 x 3 factorial arrangement of treatments. Fish- and feathermeals were prepared as pellets at 4:1 and 1:4 combinations and offered at 3.75, 11.75, and 27% of the diet. The supplements were top-dressed onto a basal diet based on corn silage that was progressively replaced by supplement. Nitrogen balance measures were made during the experiment because of the wide range in crude protein content of experimental diets. Milk protein content increased with level of supplementation in the diet reflecting the protein quality of the supplements used. There was overall higher milk DHA content when cows consumed the supplement containing more fishmeal than feather meal. Milk DHA content increased in a quadratic fashion, as more of either supplement was included in the diet. Apparent transfer efficiency of DHA from diet to milk declined with increasing amount of DHA in the diet. Results from this experiment suggest that transfer of docosahexaenoic acid from diet to milk may depend on diet composition and quantity present in the diet.     

Effects of milk fever, ketosis, and lameness on milk yield in dairy cows

The effects of milk fever, ketosis, and lameness were studied using data from 23,416 Finnish Ayrshire cows that calved in 1993 and were followed for one lactation (i.e., until culling or the next calving). Monthly test day milk yields were treated as repeated measurements within a cow in a mixed model analysis. Disease index variables were created to relate the timing of a disease to the measures of test day milk. Statistical models for each parity and disease included fixed effects of calving season, stage of lactation, and disease index. An autoregressive correlation structure was used to model the association among the repeated measurements. The milk yield of cows contracting milk fever was affected for a period of 4 to 6 wk after calving; the loss ranged from 1.1 to 2.9 kg/d, depending on parity and the time elapsed after milk fever diagnosis. Despite the loss, cows with milk fever produced 1.1 to 1.7 kg more milk/d than did healthy cows. Milk yield started to decline 2 to 4 wk before the diagnosis of ketosis and continued to decline for a varying time period after it. The daily milk loss was greatest within the 2 wk after the diagnosis, varying from 3.0 to 5.3 kg/d, depending on parity. Cows in parity 4 or higher were most severely affected by ketosis; the average total loss per cow was 353.4 kg. Lameness also affected milk yield; milk loss of cows diagnosed with foot and leg disorders varied between 1.5 and 2.8 kg/d during the first 2 wk after the diagnosis.     

Effects of milk protein genetic variants on milk yield and composition

Effects of genetic variants of the milk proteins, alpha S1-casein, beta-casein, kappa-casein and beta-lactoglobulin (beta-lg), on milk yield and composition, particularly the protein composition, were investigated in milk samples from 289 Jersey and 249 Friesian cows in eight commercial herds. Milk protein genotypes had no significant effect on yields over a complete lactation of milk and fat, but significant differences in fat content were detected for beta-casein (B, A1B, A2 greater than A1A2) and beta-lg (B, AB greater than A) variants. Significant differences between beta-lg variants were also found with total solids (B, AB greater than A), casein (B, AB greater than A), whey protein (A greater than AB greater than B) and beta-lg (A greater than AB, AC greater than B greater than BC) concentrations. Casein genotypes were not significantly different in total protein and casein concentrations but many differences were found in casein composition. alpha S1-Casein variants significantly affected alpha S1-casein (BC greater than B) and kappa-casein (B greater than BC) concentrations. beta-Casein variants affected concentration and proportion of beta-casein (A1B, A2B greater than A1, A1A2, A2, B), alpha S1-casein (A1, A2 greater than B) and kappa-casein (B greater than A2) and concentration of whey protein (A1 greater than most other beta-casein variants). kappa-Casein variants affected concentration and proportion of kappa-casein (B greater than AB greater than A), proportion of alpha S1-casein (A greater than AB greater than B) and concentrations of beta-lg (A greater than AB, B) and alpha-lactalbumin (A, AB greater than B). Differences in milk composition were found between breeds, herds and ages, and with stage of lactation. The potential use of milk protein genotypes as an aid in dairy cattle breeding is discussed.