Injection of synthetic human growth hormone-releasing factors in dairy cows. 1. Effect on feed intake and milk yield and composition

Eighteen multiparous Holstein cows in the second half of their lactation were used to determine the effect of human growth hormone-releasing factor (1-44)NH2 and a fragment of growth hormone-releasing factor (1-29)NH2 on lactational performance and feed intake. Saline, the 44-amino acid peptide or the 29-amino acid fragment, at the same dose per injection (.2 nmol.kg-1) was injected intravenously at 4-h intervals for 10 d. Average milk yield, milk composition, feed intake, and feed efficiency were compared for the second half of each 10-d preinjection, injection, and post-injection period. Injections of the 44-amino acid peptide and the 29-amino acid fragment increased milk yield 18.6 and 14.6%, respectively. Feed intake was not changed, but feed efficiency was increased 23.9 and 18.8% over control following 44-amino acid peptide and the 29-amino acid fragment injection, respectively. The lactational response was not different between the two peptides for any of the variables measured. This study demonstrates the feasibility of using a growth hormone-releasing factor fragment as an alternative method of elevating milk yield in cattle via somatotropins.     

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.     

Effect of inclusion of saliva salts in the diet on milk yield and composition in dairy cows.

Twenty multiparous Jersey cows, paired according to previous lactation yield and expected date of calving, were given two diets in a cross-over experiment in early lactation. The diets had forage: concentrate ratios maintained at 3:7, the forage being wilted grass silage and the concentrate either a proprietary dairy cake or the same cake containing saliva salts (SS) at 40 g/kg dry matter. The SS diet proved acceptable to the animals and had no effect on gestation length or calf survival. Absolute milk yields were not affected, but the SS diet caused a significant increase in the proportions of milk fat, total solids (both P less than 0.001) and protein (P less than 0.05) and in the yield of fat-corrected milk (P less than 0.001). Analysis of rumen liquor samples showed that giving the SS diet resulted in a significant increase in the molar proportion of acetate and a decrease in the proportions of propionate and to a lesser extent butyrate. Milk fat content showed significant correlations with ruminal acetate (r = 0.67), propionate (r = -0.59) and the acetate: propionate ratio (r = 0.64).     

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 fish meal protein supplementation on milk yield and composition and blood constituents of dairy cows

Ten holstein and 10 Ayrshire cows were fed diets containing undegradable intake protein from either fish meal or corn gluten meal. Cows were introduced to diets 10 d before projected calving date and individually fed blended rations until 60 d postpartum. Diets were balanced for NE1, CP, and degradable and undegradable protein. Source of undegradable protein did not affect total or FCM yields, DM intake, or milk protein percentage. Cows on fish meal diets tended to lose less BW than those on the corn gluten meal supplement (5.3 vs. 10.3% loss of initial BW). Fish meal supplementation resulted in decreased milk fat and SNF percentage (3.2 vs. 4.2% and 8.37 vs. 8.65%, respectively), but diet did not affect total milk fat, protein, or SNF yield. Plasma nonesterified fatty acids decreased and serum insulin increased with increasing weeks postpartum but were not affected by diet. In this study, no significant advantage was found to using fish meal as a source of undegradable intake protein and feed cost was higher when it was used.     

Effect of pathogen-specific clinical mastitis on milk yield in dairy cows

Our objective was to estimate the effects of the first occurrence of pathogen-specific clinical mastitis (CM) on milk yield in 3071 dairy cows in 2 New York State farms. The pathogens studied were Streptococcus spp.,Staphylococcus aureus, Staphylococcus spp., Escherichia coli, Klebsiella spp., Arcanobacterium pyogenes, other pathogens grouped together, and "no pathogen isolated." Data were collected from October 1999 to July 2001. Milk samples were collected from cows showing signs of CM and were sent to the Quality Milk Production Services laboratory at Cornell University for microbiological culture. The SAS statistical procedure PROC MIXED, with an autoregressive covariance structure, was used to quantify the effect of CM and several other control variables (herd, calving season, parity, month of lactation, J-5 vaccination status, and other diseases) on weekly milk yield. Separate models were fitted for primipara and multipara, because of the different shapes of their lactation curves. To observe effects of mastitis, milk weights were divided into several periods both pre- and postdiagnosis, according to when they were measured in relation to disease occurrence. Another category contained cows without the type of CM being modeled. Because all pathogens were modeled simultaneously, a control cow was one without CM. Among primipara, Staph. aureus, E. coli, Klebsiella spp., and "no pathogen isolated" caused the greatest losses. Milk yield generally began to drop 1 or 2 wk before diagnosis; the greatest loss occurred immediately following diagnosis. Mastitic cows often never recovered their potential yield. Among older cows, Streptococcus spp., Staph. aureus, A. pyogenes, E. coli, and Klebsiella spp. caused the most significant losses. Many multipara that developed CM were actually higher producers before diagnosis than their nonmastitic herd-mates. As in primipara, milk yield in multipara often began to decline shortly before diagnosis; the greatest loss occurred immediately following diagnosis. Milk loss persisted until at least 70 d after diagnosis for Streptococcus spp., Klebsiella spp., and A. pyogenes. The tendency for higher producing cows to contract CM may mask its impact on cow health and production. These findings provide dairy producers with more information on which pathogen-specific CM cases should receive treatment and how to manage these cows, thereby reducing CM impact on cow well being and profitability.     

Effect of concentrate feed level in late gestation on subsequent milk yield, milk composition, and fertility of dairy cows.

The effects of level of concentrate feeding in late gestation on feed intake, milk yield, milk composition, and fertility in the subsequent lactation were evaluated in a randomized block design experiment involving 60 cows. Grass silage was offered ad libitum for the last 28 d of gestation either as the sole diet (OC) or supplemented with 5 kg/d of concentrates (5C). Following calving, the cows were offered the same grass silages supplemented with 7 kg/d of concentrates. For treatments OC and 5C, total dry matter intakes were 9.28 and 11.03 kg/d of dry matter, respectively, during the last 4 wk of gestation. During wk 1 to 12 of the subsequent lactation, treatment 5C increased milk fat concentration but did not alter feed intake, milk yield, or protein concentration relative to treatment OC. Treatment 5C increased the interval to first progesterone rise and the number of services per conception relative to treatment OC. Cow parity, BF depth assessed at d 28 before parturition, and treatment provided the best fit relationships for the yields of fat and fat plus protein (R2 relationships = 0.65 and 0.64, respectively) during wk 1 to 4 of lactation. It was concluded that, other than milk fat concentration, supplementation with additional concentrates in late gestation did not alter milk yield or composition and dairy cow fertility. Furthermore, despite the very large differences in cow characteristics at d 28 before parturition, there was no evidence of any interaction between treatment and specific cow characteristics on animal performance in the first 12 wk of lactation.     

Effect of somatotropin injection and dietary protein concentration on milk yield, and kinetics of hormones in dairy cows

Four lactating Holstein cows averaging 155 d postpartum were used in a cross-over design to examine the influence of somatotropin administration (33 mg/d for 28 d) and dietary CP (11 vs. 16% CP) concentration on milk yield and kinetics of glucagon, insulin, glucose, and somatotropin. Somatotropin and dietary CP were without influence on DM intake and digestibility. Milk yields were increased by both somatotropin administration and increased dietary CP. Increased dietary CP increased turnover of glucose. Injection of somatotropin increased entry rate, pool size, and basal concentrations of somatotropin but was without effect on kinetics of glucagon, insulin, or glucose. The absence of major changes in the kinetics of hormones and glucose suggests that other factors play a role in somatotropin enhancement of milk production. However, the observed changes are consistent with the homeorhetic influence of somatotropin on milk production. Adequate dietary CP is required to obtain maximal responses to somatotropin administration.     

Short communication: prepartum photoperiod effect on milk yield and composition in dairy cows

In a previous paper we analyzed the effects of day length, the daily change in day length, and heat load prevailing on test days, and on milk yield and composition of dairy cows in hot weather. For this analysis we used milk tests of three herds in Israel between 1994 and 1996. We used the same database to analyze the effects of the day length and the daily change in day length 3 wk prepartum. The prepartum day length effect was negatively related to milk yield and to milk fat and protein percentages. The daily change in day length was negative for milk yield and lactose percentage and positive for protein content and did not affect fat content. The difference of 4 h between the shortest and the longest day, plus the seasonal change in day length, accounted for the addition of 1.9 kg of milk/d for a cow calving after the shortest day compared with a cow calving after the longest day. The difference in milk composition between these two cows was estimated to be 0.27 and 0.08% of fat and protein, respectively.     

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.     

Effect of modified dry period lengths and bovine somatotropin on yield and composition of milk from dairy cows

Dry periods of 40 to 60 d have been an industry standard because dry periods <40 d have resulted in reduced milk yields in the subsequent lactation by 10 to 30%. However, recent research has demonstrated no production losses for cows given a 30-d dry period. The current study evaluated milk production effects of shortened or omitted dry periods for cows at mature-equivalent production >12,000 kg of milk and treated with bovine somatotropin (bST). The study used 2 commercial dairies and one university dairy and included 4 treatments. Five multiparous and 5 primiparous cows from each farm were assigned to each treatment: 1) 60-d dry period, label use of bST (60DD); 2) 30-d dry period, label use of bST (30DD); 3) continuous milking, label use of bST (CMLST); and 4) continuous milking with continuous use of bST (CMCST). Per label, bST use started at 57 to 70 d in milk and ended 14 d before drying (60DD and 30DD) or expected calving date (CMLST). In primiparous cows, average milk yields during the first 17 wk of lactation were reduced for cows on treatments 30DD, CMLST, and CMCST vs. the 60DD treatment. (38.3, 35.1, and 37.5 vs. 44.1 +/- 1.3 kg/d, respectively). For multiparous cows, respective milk yields did not differ (46.6, 43.4, 46.5, and 47.7 +/- 2.1 kg/d). Shortened or omitted dry periods may impede mammary growth in primiparous cows, resulting in reduced milk yield in the subsequent lactation. In contrast, a shortened or omitted dry period with either bST protocol did not alter production in multiparous cows treated with bST. Quality aspects of prepartum milk and colostrum require additional characterization. For multiparous cows, milk income generated for short dry periods or for continuous milking might increase their profitability. At 17 wk of the subsequent lactation, estimates of the cumulative net margins of multiparous cows on the 30DD treatment and continuous milking treatments exceeded those of cows on the 60DD treatment by 40 dollars to 60 dollars per cow.     

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.     

Digestion,milk production,milk composition,and blood composition of dairy cows fed whole flaxseed

A total of 90 lactating Holstein cows averaging 628 kg (SE = 8) of body weight (BW) were allotted at calving to 30 groups of three cows blocked for similar calving dates to determine the effects of feeding whole untreated flaxseed on milk production and composition, fatty acid composition of blood and milk, and digestibility, and to determine whether flaxseed could substitute for other sources of fat such as Megalac and micronized soybeans. Cows were fed a total mixed diet based on grass and corn silage and fat supplements for ad libitum intake. The experiment was carried out from calving up to wk 16 of lactation. Cows within each block were assigned to one of the three isonitrogenous, isoenergetic, and isolipidic supplements based on either whole flaxseed (FLA), Megalac (MEG), or micronized soybeans (SOY). Intake of dry matter and change in BW were similar among diets. Cows fed FLA had greater milk yield than those fed MEG (35.7 vs. 33.5 kg/d) and there was no difference between cows fed FLA and those fed SOY (34.4 kg/d). Fat percentage was higher in the milk of cows fed MEG (4.14%) than in the milk of those fed FLA (3.81%) or SOY (3.70%), but milk protein percentage was higher for cows fed FLA (2.98%) than for those fed MEG (2.86%) and SOY (2.87%). Digestibilities of acid detergent fiber, neutral detergent fiber, and ether extract were lower for cows fed FLA than for those fed SOY and MEG. Retention of N was similar among diets. Feeding FLA resulted in the lowest omega-6-to-omega-3-fatty-acids ratio, which would improve the nutritive value of milk from a human health point of view. The data suggest that micronized soybeans and Megalac can be completely substituted by whole untreated flaxseed as the fat source in the diet of early lactating cows without any adverse effect on production and that flaxseed increased milk protein percentage and its omega-6-to-omega-3-fatty-acids ratio.     

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.     

Effect of dry period length and dietary energy source on energy balance,milk yield,and milk composition of dairy cows

The objective of this study was to evaluate the effects of dry period length and dietary energy source in early lactation on milk production, feed intake, and energy balance (EB) of dairy cows. Holstein-Friesian dairy cows (60 primiparous and 108 multiparous) were randomly assigned to dry period lengths (0, 30, or 60 d) and early lactation ration (glucogenic or lipogenic), resulting in a 3 × 2 factorial design. Rations were isocaloric and equal in intestinal digestible protein. The experimental period lasted from 8 wk prepartum to 14 wk postpartum and cows were monitored for milk yield, milk composition, dry matter intake (DMI), energy balance, and milk fat composition. Prepartum average milk yield for 60 d precalving was 13.8 and 7.7 ± 0.5 kg/d for cows with a 0- and 30-d dry period, respectively. Prepartum DMI and energy intake were greater for cows without a dry period and 30-d dry period, compared with cows with a 60-d dry period. Prepartum EB was greater for cows with a 60-d dry period. Postpartum average milk yield until wk 14 was lower for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period (32.7, 38.7, and 43.3 ± 0.7 kg/d for 0-, 30-, and 60-d dry period, respectively). Postpartum DMI did not differ among treatments. Postpartum EB was greater for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period. Young cows (parity 2) showed a stronger effect of omission of the dry period, compared with a 60-d dry period, on additional milk precalving (young cows: 15.1 kg/d; older cows: 12.0 kg/d), reduction in milk yield postcalving (young cows: 28.6 vs. 34.8 kg/d; older cows: 41.8 vs. 44.1 kg/d), and improvement of the EB postcalving (young cows: 120 vs. −93 kJ/kg^0.75·d; older cows: −2 vs. −150 kJ/kg^0.75·d. Ration did not affect milk yield and DMI, but a glucogenic ration tended to reduce milk fat content and increased EB, compared with a more lipogenic ration. Reduced dry period length (0 and 30 d) increased the proportion of short- and medium-chain fatty acids in milk fat and omitting the dry period decreased the proportion of long-chain fatty acids in milk fat. In conclusion, shortening and omitting the dry period shifts milk yield from the postpartum to the prepartum period; this results in an improvement of the EB in early lactation. An increased energy status after a short dry period can be further improved by feeding a more glucogenic ration in early lactation.     

Effect of stress on blood leucocyte and milk somatic cell counts in dairy cows.

Blood and milk samples from Holstein cows were examined for total blood leucocyte count, differential blood leucocyte count, milk quality test, and somatic cell count in milk while the cows were stressed by corticotropin injection, confinement in a heat-humidity chamber, or environmental-heat stress by exposure during the hot summer months of June through November in southern Arizona. All three stressing conditions resulted in a moderate blood leucocytosis. Modest increases in somatic cell counts of milk were associated with corticotropin injection and environmental-heat stress. Positive correlations were recorded between blood leucocytes and somatic cell counts of milk in mastitis-free cows injected with corticotropin and between percent blood neutrophils and somatic cell counts of milk in environmental-heat stressed cows with no evidence of current mastitis.