Effect of somatotropin on kinetics of nonesterified fatty acids and partition of energy, carbon, and nitrogen in lactating dairy cows

The utilization of energy, carbon, and nitrogen, and irreversible loss rates of nonesterified fatty acids were examined in lactating cows during treatment with bovine somatotropin. Six multiparous Holstein cows at approximately 62 d postpartum received daily intramuscular injections of somatotropin (29.4 mg/d) or excipient during two 21-d treatment periods in a crossover experimental design. Milk yield was increased 11% (37.1 versus 41.3 kg/d), whereas intake and digestibility of DM, energy, nitrogen, and carbon were not affected. Cows remained near zero net energy balance during both treatments (1.31 versus -1.52 Mcal/d for control and somatotropin, respectively). The major effect of somatotropin was to partition net energy into milk while tissue energy accretion was reduced. Postabsorptive use of nitrogen and carbon was altered by somatotropin as reflected by greater secretion in milk. Urinary losses of nitrogen and tissue use of carbon were reduced. Plasma concentrations and irreversible loss rates of nonesterified fatty acids did not differ between treatments. Somatotropin treatment of lactating cows results in partitioning of nutrients away from tissue deposition toward milk synthesis. The extent to which different metabolic processes are altered depends upon the energy balance of the somatotropin-treated animal.     

Duodenal infusion of glucose decreases milk fat production in grass silage-fed dairy cows

Four lactating dairy cows were arranged in a 4 x 4 Latin square design to study the effect of intestinal glucose supply on milk fat synthesis. Glucose (0, 443, 963, and 2398 g/d) was continuously infused in the duodenum over 14-d periods. Grass silage-based diets were formulated to be isoenergetic and isonitrogenous and met 100 and 110% of energy and protein requirements according to INRA (1989). Mammary uptake of nutrients was estimated through assay of arteriovenous differences and blood flow measurements. Glucose infusions decreased arterial concentrations of acetate, beta-hydroxybutyrate, and nonesterified fatty acids linearly and total glycerides curvilinearly. Milk fat yield was slightly decreased (- 52 g/d) between 0 and 963 g/d of glucose and milk fatty acid composition was modified by a marked decrease in long-chain fatty acids and an increase in de novo synthesis. The decrease in long-chain fatty acids, related to the decreased mammary uptake of plasma total glycerides, was likely due to a decrease in lipoprotein lipase and esterification activities. In regards to the evolution of metabolite concentrations in milk, the enhanced de novo synthesis and chain elongation was probably allowed by a greater availability of NADPH synthesized through pentose phosphate pathway. The greatest dose of glucose clearly decreased milk fat yield (-234 g/d). A mammary cell mediated intracellular reaction likely caused a homothetic decrease in milk fatty acids. However, reduced synthesis was not due to a shortage of glycerol-3-phosphate because its milk concentration remained unchanged. In conclusion, changes in exogenous glucose supply, in cows fed a grass silage-based diet, decreased milk fat production and modified milk fatty acid composition.     

Short communication: Hepatic gene expression for gluconeogenic enzymes in lactating dairy cows treated with bovine somatotropin

Eight lactating Holstein dairy cows (80 d in milk) were used to examine the effects of exogenous bovine somatotropin (bST) on hepatic contents of mRNA encoding pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK), and microsomal triglyceride transfer protein (MTP). Concentrations of bST in plasma were higher and milk production increased 20% in bST-treated cows. Liver samples from cows treated with bST had significantly higher total lipid contents than those from control cows. Although there were small numerical tendencies, neither triglyceride concentrations in liver nor nonesterified fatty acids (NEFA), beta-hydroxybutyrate (BHBA), or glucose in plasma differed significantly between bST-treated and control cows. Short-term bST treatment had no detectable effects on contents of PC, PEPCK, and MTP mRNA in the liver. In summary, exogenous bST stimulation of milk production is not mediated through enhanced liver gluconeogenesis, but may involve partitioning of glucose and fatty acids for preferential use by the mammary gland.     

trans-10, cis-12 conjugated linoleic acid decreases lipogenic rates and expression of genes involved in milk lipid synthesis in dairy cows

Feeding conjugated linoleic acid (CLA) reduces milk fat synthesis in lactating dairy cows, and the effect has been shown to be specific for the trans-10, cis-12 CLA isomer. Our objectives were to examine potential mechanisms by which trans-10, cis-12 CLA inhibits milk fat synthesis. Multiparous Holstein cows (n = 4) in late lactation were used in a balanced 2 x 2 crossover design. Treatments consisted of a 5 d abomasal infusion of either skim milk (control) or purified trans-10, cis-12 CLA (13.6 g/d) emulsified in skim milk. On d 5 of infusion, mammary gland biopsies were performed and a portion of the tissue analyzed for mRNA expression of acetyl CoA carboxylase, fatty acid synthetase, delta 9-desaturase, lipoprotein lipase, fatty acid binding protein, glycerol phosphate acyltransferase and acylglycerol phosphate acyltransferase. Lipogenic capacity was evaluated with another portion of the tissue. Infusion of trans-10, cis-12 CLA decreased milk fat content and yield 42 and 48%, respectively and increased the trans-10, cis-12 CLA content in milk fat from < 0.1 to 4.9 mg/g. Reductions in milk fat content of C4 to C16 fatty acids contributed 63% to the total decrease in milk fat yield (molar basis). Analysis of the ratios of specific fatty acid pairs indicated trans-10, cis-12 CLA also shifted fatty acid composition in a manner consistent with a reduction in delta 9-desaturase. Mammary explant incubations with radiolabeled acetate established that lipogenic capacity was decreased 82% and acetate oxidation to CO2 was reduced 61% when cows received trans-10, cis-12 CLA. Infusing trans-10, cis-12 CLA also decreased the mRNA expression of all measured enzymes by 39 to 54%. Overall, data demonstrated the mechanism by which trans-10, cis-12 CLA inhibits milk fat synthesis includes decreasing expression of genes that encode for enzyme involved in circulating fatty acid uptake and transport, de novo fatty acid synthesis, desaturation of fatty acids and triglyceride synthesis.     

Duodenal rapeseed oil infusion in early and midlactation cows. 5. Milk fatty acids and adipose tissue lipogenic activities

Lipogenic activities of perirenal adipose tissue were investigated in early (wk 3) and midlactation (wk 19 to 26) cows that received a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In midlactation, oil infusion resulted in a decreased rate of fatty acid synthesis from acetate and a decreased rate of the activities of fatty acid synthetase and glucose-6-phosphate dehydrogenase, whereas lipoprotein lipase activity tended to increase. The rate of glucose incorporation into glyceride-glycerol and the activities of glycerol-3-phosphate dehydrogenase and malic enzyme were not significantly affected. Fatty acid C14:0 content of perirenal adipose tissue was decreased, and fatty acid C18:2 and C18:3 contents were increased in oil-infused cows. In early lactation, rates of acetate incorporation into fatty acids and activities of fatty acid synthetase and lipoprotein lipase were very low. Activities of glucose-6-phosphate dehydrogenase and glycerol-3-phosphate dehydrogenase were lower in the early than in the midlactation trial. Oil infusion did not change the measured parameters. In both trials, percentages and yields of milk fatty acids C18:1, C18:2, and C18:3 were increased, whereas those of C14:0 and C16:0 were decreased by oil. Calculated transfer rates of absorbed fatty acid C18:2 from oil to milk fat were 16 to 26%. Results suggested that oil fatty acids affected adipose and mammary de novo lipogenesis in a direct way without affecting fatty acid esterification in adipose tissue or total fat secretion in mammary tissue.     

Addition of fish oil to diets for dairy cows. II. Effects on milk fat and gene expression of mammary lipogenic enzymes

Sixteen Holstein cows in mid-lactation were used to determine whether alterations of mammary fatty acid metabolism are responsible for the milk fat depression associated with consumption of fish oil. Cows were given a total mixed ration with no added fish oil (control), unprotected fish oil (3.7 % of dry matter), or glutaraldehyde-protected microcapsules of fish oil (1.5% or 3.0% of dry matter) for 4 weeks. Milk samples were taken once a week and a mammary biopsy was taken from a rear quarter at the end of the treatment period. Milk fat content was lower in cows given unprotected fish oil (26.0 g/kg), 1.5% protected fish oil (24.6 g/kg) and 3% protected fish oil (20.4 g/kg) than in cows fed the control diet (36.0 g/kg). This was mainly due to a decrease in the synthesis of short-chain fatty acids. Consumption of protected fish oil decreased the abundance of lipogenic enzymes mRNA in the mammary gland. Acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase mRNAs for cows given 3% protected fish oil averaged only 30%, 25% and 25% of control values, respectively. Dietary addition of unprotected fish oil slightly decreased mRNA abundance of these enzymes but markedly reduced the amount of lipoprotein lipase mRNA. Milk fat content was significantly correlated with gene expression of acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase but not lipoprotein lipase. These results suggest that fish oil reduces milk fat percentage by inhibiting gene expression of mammary lipogenic enzymes.     

Long-acting insulins alter milk composition and metabolism of lactating dairy cows

This study investigated the effect of 2 different types of long-acting insulin on milk production, milk composition, and metabolism in lactating dairy cows. Multiparous cows (n = 30) averaging 88 d in milk were assigned to one of 3 treatments in a completely randomized design. Treatments consisted of control (C), Humulin-N (H; Eli Lilly and Company, Indianapolis, IN), and insulin glargine (L). The H and L treatments were administered twice daily at 12-h intervals via subcutaneous injection for 10 d. Cows were milked twice daily, and milk composition was determined every other day. Mammary biopsies were conducted on d 11, and mammary proteins extracted from the biopsies were analyzed by Western blot for components of insulin and mammalian target of rapamycin signaling pathways. Treatment had no effect on dry matter intake or milk yield. Treatment with both forms of long-acting insulin increased milk protein content and tended to increase milk protein yield over the 10-d treatment period. Analysis of milk N fractions from samples collected on d 10 of treatment suggested that cows administered L tended to have higher yields of milk protein fractions than cows administered H. Milk fat content and yield tended to be increased for cows administered long-acting insulins. Lactose content and yields were decreased by treatment with long-acting insulins. Administration of long-acting insulins, particularly L, tended to shift milk fatty acid composition toward increased short- and medium-chain fatty acids and decreased long-chain fatty acids. Plasma concentrations of glucose and urea N were lower for cows administered long-acting insulins; interactions of treatment and sampling time were indicative of more pronounced effects of L than H on these metabolites. Concentrations of nonesterified fatty acids and insulin were increased in cows administered long-acting insulins. Decreased concentrations of urea N in both plasma and milk suggested more efficient use of N in cows administered long-acting insulins. Western blot analysis of mammary tissue collected by biopsy indicated that the ratios of phosphorylated protein kinase b (Akt) to total Akt and phosphorylated ribosomal protein S6 (rpS6) to total rpS6 were not affected by long-acting insulins. Modestly elevating insulin activity in lactating dairy cows using long-acting insulins altered milk composition and metabolism. Future research should explore mechanisms by which either insulin concentrations or insulin signaling pathways in the mammary gland can be altered to enhance milk fat and protein production.     

Short-term administration of bovine somatotropin to lactating dairy cows in a subtropical environment

Our objective was to evaluate response of lactating dairy cows to daily injections of bovine somatotropin during a subtropical summer. Ten Holstein cows, averaging 196 d in lactation, were used in a 30-d study. No treatment was imposed during d 1 to 10 (period 1) and d 21 to 30 (period 3). During d 11 to 20 (period 2), cows were injected daily with either 0 or 59 IU of pituitary-derived bovine somatotropin in 30 ml solution. Dry matter intake and milk yield and composition were measured daily. Jugular blood samples, taken on d 10, 15, 20, and 30, were analyzed for insulin, nonesterified fatty acids, urea nitrogen, and insulin-like growth factor-1. Body temperatures and respiration rates were measured at 1400 h on 4 or 5 d during each 10-d period. Data were analyzed using orthogonal contrasts. Contrast of period 1 plus period 3 vs. period 2 for treatment X days interaction was significant for milk yield, respiration rate, serum nonesterified fatty acids, and insulin-like growth factor-1. Under heat stress, cows injected with bovine somatotropin for 10 d produced 9.3% more milk than control cows with no change in feed intake. This increased production was accompanied by higher respiration rates (6%) and higher concentrations of serum nonesterified fatty acids (150%) and insulin-like growth factor-1 (222%).     

Feeding Calcium Salts of Fatty Acids to Lactating Cows

Digestibility and production responses to feeding Ca salts of fatty acids were determined in lactating cows. Cows 120 d in milk were fed 4% of DM as Ca salts of fatty acids using chromium oxide mordanted corn silage as unabsorbed reference substance. Digestion of DM and N did not change, fatty acid digestion increased, and Ca percentage absorption decreased. Milk and milk fat production were enhanced.In production experiments in Pennsylvania, cows in early lactation were fed 54% of total diet as roughage and .45 kg/d Ca salts of fatty acids. Milk increased by 4% and FCM by 6%. Plasma somatotropin decreased, and insulin was not changed. In similar experiments in Israel with 31% of total diet as roughage, feeding .5 kg/d Ca salts of fatty acids to cows following parturition enhanced milk by 5% and FCM by 9.5%. The production increment of Ca salts of fatty acids decreased following peak lactation. No after effects of feeding Ca salts were observed. Body weight changes and rumen VFA were similar, whereas DM intake was .9 kg less and plasma FFA decreased with feeding Ca salts. It is concluded that inclusion of Ca salts of fatty acids in early lactation enhances production of milk and FCM.     

Milk lipoprotein lipase activity during long-term administration of recombinant bovine somatotropin

The effect of long-term administration of recombinant bovine somatotropin to dairy cows on milk lipoprotein lipase activity was investigated. Recombinant bovine somatotropin was administered daily to 32 cows (8/treatment). Treatments were 0 (control), 12.5, 25.0, and 50.0 mg/d or recombinant bovine somatotropin administered in once daily intramuscular injections. Treatments began at 28 to 35 d of lactation and continued until 294 d of lactation. Recombinant bovine somatotropin treatments had no significant effect on milk lipoprotein lipase activity; enzyme activity for each treatment was 97.87, 108.96, 99.96, and 92.43 units/ml of milk, respectively. A significant effect of the stage of lactation was unrelated to recombinant bovine somatotropin administration. Enzyme activity peaked at approximately 20 wk of the treatment or 25 wk postpartum. These results indicate that long-term administration of recombinant bovine somatotropin does not alter the processes that lead to lipoprotein lipase activity in milk.     

Effect of conjugated linoleic acid and acetate on milk fat synthesis and adipose lipogenesis in lactating dairy cows

During biohydrogenation-induced milk fat depression (MFD), nutrients are spared from milk fat synthesis and are available for other metabolic uses. Acetate is the major carbon source spared and it may increase lipid synthesis in adipose tissue during MFD. The objective of this study was to compare the effect of trans-10,cis-12 conjugated linoleic acid (CLA) and the amount of acetate spared during CLA-induced MFD on adipose tissue lipogenesis. Nine multiparous, lactating, ruminally cannulated Holstein cows (244 ± 107 d in milk; 25 ± 8.4 kg of milk/d; mean ± standard deviation) were randomly assigned to treatments in a 3 × 3 Latin square design. Experimental periods were 4 d followed by a 10-d washout. Treatments were control (CON), ruminal infusion of acetate (AC; continuous infusion of 7 mol/d adjusted to pH 6.1 with sodium hydroxide), or abomasal infusion of CLA (10 g/d of both trans-10,cis-12 CLA and cis-9,trans-11 CLA). Dry matter intake, milk yield, and milk protein yield and percentage were not affected by treatments. Compared with CON, milk fat yield decreased 23% and fat percent decreased 28% in CLA, and milk fat yield increased 20% in AC. Concentration and yield of milk de novo synthesized fatty acids (<C16) were reduced and concentration of preformed fatty acids (>C16) was increased by CLA, compared with CON. Yield of de novo synthesized fatty acids and palmitic acid was increased by AC, compared with CON. Lipogenesis capacity of adipose tissue explants was decreased 72% by CLA, but was not affected by AC. Acetate oxidation by adipose explants was not affected by treatments. Treatments had no effect on expression of key lipogenic factors, lipogenic enzymes, and leptin; however, expression of fatty acid binding protein 4 was reduced in CLA compared with CON. Additionally, hormone-sensitive lipase and perilipin 1 were decreased by CLA and acetate. Plasma glucose and glucagon concentrations were not affected by treatments; however, CLA increased nonesterified fatty acids 17.7%, β-hydroxybutyrate 16.1%, and insulin 27.8% compared with CON, and AC increased plasma β-hydroxybutyrate 18%. In conclusion, during CLA-induced MFD in low-producing cow adipose tissue was sensitive to the anti-lipogenic effects of CLA, while spared acetate did not stimulate adipose lipogenesis. However, acetate may play an important role in stimulating lipogenesis and improving energy status in the mammary gland under normal conditions.     

Effect of added dietary fat and bovine somatotropin on the performance and metabolism of lactating dairy cows

Four early lactation Holstein cows (44 to 105 d postpartum) were used in a 4 X 4 Latin square experiment in a 2 X 2 factorial arrangement of treatments to study effects of added dietary fat and/or bovine somatotropin on performance and metabolism. Treatments were: 1) control diet plus placebo injection; 2) 5% added dietary fat (hydrolyzed blend of animal and vegetable fat) + placebo injection; 3) control diet + 50 IU bovine somatotropin/d; and 4) 5% added dietary fat + 50 IU bovine somatotropin/d. Dietary fat reduced dry matter intake (21.6 vs. 22.7 kg/d) and elevated plasma triglycerides (34.7 vs. 29.2 mg/100 ml). Injection of somatotropin lowered blood urea nitrogen, increased plasma free fatty acids, and increased plasma somatotropin. Milk production, milk fat percent, and 4% FCM production were increased by the injection of somatotropin. Milk protein percent was decreased (3.30 vs. 3.44%) with added fat and tended to be lower with somatotropin. The percentage of short-chain fatty acids (C6 to C14) in milk fat decreased with added fat while the percentage of stearic and oleic acids in milk fat increased. Production responses for fat plus somatotropin and somatotropin treatments were similar. Under the conditions of this study, the addition of dietary fat with injection of somatotropin had little effect on production parameters compared with that found with somatotropin alone.     

Roles of acetate and its interactions with glucose and lactate in cow mammary tissue

Slices from mammary glands from six lactating Holstein cows were incubated in Krebs-Ringer bicarbonate-based media in the presence of varying concentrations of acetate, glucose, and lactate. Conversions of acetate to carbon dioxide, fatty acids, citrate, glyceride-glycerol, and lactose were determined. Specific effects of beta-hydroxybutyrate and stearate availability also were evaluated. Utilization of acetate for all functions usually followed Michaelis-Menten kinetics with apparent affinities in the physiological concentration range of acetate. Availability of glucose had a large "permissive" effect on acetate to conversion to fatty acids. However, acetate metabolism was independent of the availability of lactate. Conversion of acetate to glyceride-glycerol was significant. This indicates the possibility of bidirectional glycolytic flux, which could limit glucose conversion to fatty acids. Addition of stearate caused general increases of acetate metabolism. Conversion of acetate to fatty acids, carbon dioxide, and citrate was elevated in the absence of beta-hydroxybutyrate. The latter observation indicates beta-hydroxybutyrate may not be a required initiator of fatty acid synthesis in mammary tissue.     

Responses of dairy cows in early lactation to bovine somatotropin and ruminally inert fat

Bovine somatotropin (0 or 41.2 mg/d bST) and calcium salts of long-chain fatty acids (0 or .77 kg/d Ca-LCFA) were administered to 16 Holstein cows in early lactation. Cows remained on 0 or 41.2 mg/d bST for the entire 10 wk and received 0 or .77 kg/d Ca-LCFA in one of two 5-wk periods. Production data were recorded daily, milk fatty acids, and blood metabolites were determined once each period. Treatments did not affect feed intake. Fat-corrected milk (kg/d) and percentage of milk fat for cows receiving no supplementation, fatty acids alone, bST alone, and fatty acids and bST together were 33.8, 3.2; 33.5, 3.1; 37.4, 3.4; and 40.8, 3.5. Milk fatty acids below C16 were reduced with either bST or dietary fatty acids; C16 fatty acids were lower with bST but higher with dietary fatty acids; C18:0 fatty acids were reduced with dietary fatty acids; and C18:1 fatty acids were higher with either bST or dietary fatty acids. Blood acetoacetate concentrations were higher with both bST and dietary fatty acids, beta-hydroxybutyrate was not different, and FFA and insulin concentrations increased with bST. In this experiment, the energy supplied by Ca-LCFA acids enhanced the lactogenic effect of bST.     

Feeding calcium soaps of fatty acids to lactating cows: effect on production, body condition and blood lipids

Ca soaps of fatty acids (CSFA, 0.5 kg/d) were added to the diet of lactating cows for 170 d, and production, body condition score and blood lipids were examined. Production of fat-corrected milk was increased by 1.5 kg/d owing to increase in both milk and fat production. Over 250 d lactation, production of fat-corrected milk was enhanced by 1.3 kg/d. Body condition scores were lower in cows fed CSFA in early lactation, but tended to exceed those of control cows after 80 d lactation. Reproductive performance was improved in cows fed CSFA. Serum total lipids, phospholipids and cholesterol were increased in CSFA cows at 15 and 29 d but not at 59 d post partum. The cholesterol increase was mainly in the high density lipoprotein fraction.     

Model to describe and alleviate milk protein depression in early lactation dairy cows fed a high fat diet

The depression of milk protein percentages for cows fed high fat diets in early lactation is a major problem facing the dairy industry. In order to describe more fully the mechanism involved, data involved 97 cows observations were summarized. Cows were fed diets containing corn-soybean meal or additional fat in the form of whole oilseeds as the main ingredients in the concentrate mix. Blood samples from the tail artery and subcutaneous abdominal vein were taken approximately 6- to 8-wk postpartum for amino acid analyses. Production of milk during the week of blood sampling was increased (36.9 and 39.6 kg/d) approximately 7.3% but milk protein percentages (2.91 and 2.79) were reduced for cows fed added fat. Intake of DM (21.1 and 21.4 kg/d) and BW (605 and 608 kg) were similar. Uptake of amino acids by the mammary gland, as measured by arteriovenous differences, was numerically lower for all essential amino acids and significantly reduced for histidine, isoleucine, leucine, phenylalanine, threonine, valine, and total essential amino acids for cows fed added fat. It is proposed that added fat inhibits somatotropin release from the anterior pituitary, thereby reducing mammary gland uptake of amino acids because of the role of somatotropin in aiding amino acid uptake. Administration of exogenous somatotropin with added fat diets may alleviate milk protein depression associated with such diets.     

Feeding micronized and extruded flaxseed to dairy cows: effects on blood parameters and milk fatty acid composition

Four lactating Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design to determine the effects of feeding micronized and extruded flaxseed on milk composition and blood profile in late lactation. Four diets were formulated: a control (C) diet with no flaxseed, a raw flaxseed (RF) diet, a micronized flaxseed (MF) diet, and an extruded flaxseed (EF) diet. Flaxseed diets contained 12.6% flax-seed (dry matter basis). Experimental periods consisted of 21 d of diet adaptation and 7 d of data collection. Feeding flaxseed reduced milk yield and energy-corrected milk by 1.8 and 1.4 kg/d, respectively. Yields of milk protein and casein were also lower for cows fed flaxseed diets than for those fed the C diet. Milk yield (1.6 kg/d) and milk fat percentage (0.4 percentage unit) were lower for cows fed EF than those fed MF. Plasma cholesterol and nonesterified fatty acid concentrations were higher for cows fed flaxseed diets relative to those fed the C diet. Flaxseed supplementation decreased plasma concentrations of medium-chain (MCFA) and saturated (SFA) fatty acids and increased concentrations of long-chain (LCFA) and monounsaturated fatty acids. Feeding flaxseed reduced the concentrations of short-chain fatty acids (SCFA), MCFA, and SFA in milk fat. Consequently, concentrations of LCFA and unsaturated fatty acids were higher for cows fed flaxseed diets than for those fed the C diet. Flaxseed supplementation increased average concentrations of C(18:3) and conjugated linoleic acid by 152 and 68%, respectively. Micronization increased C(18:3) level, and extrusion reduced concentrations of SCFA and SFA in milk. It was concluded that feeding raw or heated flaxseed to dairy cows alters blood and milk fatty acid composition. Feeding extruded flaxseed relative to raw or micronized flaxseed had negative effects on milk yield and milk composition.     

Effects of recombinant bovine somatotropin on milk production, body composition, and physiological parameters

Twenty-eight multiparous Holstein cows were utilized to determine effects of long-term administration of recombinant bovine somatotropin on lactational performance, body condition, body composition, hormones, blood constituents, and physiological parameters. Treatments were 0 (control), 10.3, 20.6, and 41.2 mg recombinant bovine somatotropin administered daily as subcutaneous injections beginning 4 to 5 wk postpartum and continuing for 38 wk. A total mixed diet of 28% corn silage, 22% alfalfa hay cubes, and 50% corn-soybean meal-based grain mixture was fed. Fat-corrected milk yields were increased 12 to 25% for cows treated with somatotropin as compared with controls (29.9 kg/d). Milk composition was similar among treatments. Cows receiving somatotropin consumed 4 to 10% more feed and were 11 to 17% more efficient than controls for conversion of feed to milk. Body weight changes were not significantly different among treatments, but cows receiving somatotropin gained 4 to 10% less weight than controls. Body fat (kg) of cows receiving 20.6 and 41.2 mg/d was less than that of cows receiving 10.3 mg/d or no somatotropin. Estimated weights of body protein and mineral, most blood constituents, respiratory rates, and body temperature were not affected by somatotropin administration. Plasma fatty acids were elevated and hematocrit values were reduced. Plasma insulin, serum somatotropin, and heart rate increased concurrently with somatotropin administration.     

Metabolic and production responses to dietary protein and exogenous somatotropin in late gestation dairy cows.

Forty-three multiparous Holstein cows were used in a completely randomized design to evaluate the effects of protein supplementation and the use of bovine somatotropin (bST; Posilac, Monsanto Co., St. Louis, MO) in late gestation on animal metabolism and productivity in the periparturient period. Treatments were initiated 28 d prior to expected calving date and continued through parturition. Diets contained either 13.3 or 17.8% crude protein and were formulated to be similar in profile of protein fractions. Within each dietary treatment, cows were assigned to receive either 0 or 500 mg of sustained released bST once every 14 d until parturition. Following parturition, all cows were subjected to the same management and dietary treatments, and production measurements were followed until 42 d in milk. The use of bST increased plasma glucose and decreased plasma nonesterified fatty acids and beta-hydroxybutyrate prior to calving. Despite these changes in metabolism, bST did not affect concentrations of fat and triglyceride in the liver prepartum or postpartum. Feeding the 17.8% protein diet failed to stimulate glucose metabolism and tended to elevate plasma beta-hydroxybutyrate in late gestation. Cows treated with bST produced 3.3 kg/d more milk than did controls across the first 42 d of lactation; the difference was 4.6 kg/d in wk 6 of lactation. The use of bST in late gestation has considerable promise to alter cow metabolism positively. The results of these and other possible periparturient responses to somatotropin may increase milk production in early lactation.     

Extruded blend of soybean meal and sunflower seeds for dairy cattle in early lactation

An extruded blend of 44% crude protein soybean meal (50%), whole sunflower seeds (45%), and premix (5%) was evaluated as a protein and energy source for dairy cows in early lactation. Thirty Holstein cows (24 multiparous and 6 primiparous) were assigned to either a corn-oats-soybean meal concentrate or a concentrate where soy-sunflower blend replaced all soybean meal and portions of corn and oats. Dry matter of total mixed diets was 36% corn silage, 21% alfalfa haylage, and 43% concentrate. Yields of milk (33.6 and 33.8 kg/d) and 4% fat-corrected milk (30.9 and 30.5 kg/d) were similar, and percentages of total solids (11.92 and 11.38), fat (3.55 and 3.30), and protein (2.91 and 2.74) were lower in milk from cows fed soy-sunflower blend. Milk from cows fed soy-sunflower blend contained fewer short- and medium-chain fatty acids, more 18-carbon fatty acids, and was more unsaturated than from cows fed soybean meal. Intakes of dry matter and changes in body weight were not different among diets. Ruminal fluid pH and molar ratio of acetate to propionate were higher, and concentrations of total volatile fatty acids and ammonia were lower in cows fed soy-sunflower blend. Concentrations of essential amino acids in arterial serum, calculated mammary uptakes, and transfer efficiencies indicated more desirable amino acid balance in cows fed soy-sunflower blend. Methionine appeared to be most limiting with both diets.