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Forty-one Holstein cows were injected with 0, 5, or 14 mg/d of bST for the last 46 +/- 6 d before parturition. Compared with data for controls, the 5- and 14-mg doses of bST increased apparent protein synthesis about 16% before parturition. Exogenous bST before parturition increased apparent protein degradation 30% during wk 1 after parturition. During wk 1 of lactation, 14 mg of bST also increased milk protein yield 33%. No treatment differences were present in concentration of serum NEFA, body condition score, or thickness of subcutaneous fat. Therefore, administration of bST before parturition did not alter metabolism of subcutaneous fat. Prepartum treatment with 5 and 14 mg of bST increased and maintained serum somatotropin at 6.5 and 22.7 ng/ml, respectively, compared with 1.6 ng/ml in controls. Concentrations of serum IGF-I were initially increased but were not maintained as parturition approached. On d -23, IGF binding protein 3 was increased 65% but was not different among groups by d -7. For groups administered the 5 and 14 mg/d of bST, IGF binding protein 2 was decreased 40%. Administration of bST before parturition increased protein reserves and stimulated milk protein yield for 1 wk but did not alter metabolism of subcutaneous fat. Furthermore, energy balance appeared to be a major regulator of concentrations of IGF binding protein 3 and responsiveness of IGF-I to exogenous somatotropin before parturition.

Two experiments were conducted to ascertain lysine required for maintenance and milk production in lactating dairy cows. Multiparous Holstein cows fitted with abomasal cannulas were utilized in a replicated 3 x 3 extra-period Latin square design and infused with 0, 45, or 90 g of L-lysine-HCl daily (Experiment 1). In Experiment 2, 12 cows were utilized in a 5 x 5 Latin square design (with 2 replacement cows) and infused with 0, 22.5, 45, 90, and 180 g of L-lysine-HCl daily. Cows were housed in comfort stalls, milked at 0600 and 1700 h, exposed to a 16:8 h light:darkness cycle, and fed for ad libitum intake a 15.7% CP diet formulated to contain approximately 75% of dietary protein from corn-based feed ingredients. Milk yield was not affected in Experiment 1, but milk production increased linearly with lysine infusion level in Experiment 2. A linear response in daily yield of milk protein to lysine infusion was observed in both experiments. As lysine infusion increased, coccygeal plasma lysine concentrations tended to increase in Experiment 1, but in Experiment 2 free lysine increased linearly and quadratically in coccygeal plasma and increased linearly in plasma from the subcutaneous abdominal vein. The quadratic response in plasma free lysine (Experiment 2) suggested that lysine was the limiting AA for milk production from the composite protein flow to the small intestine. Using break-point analysis of plasma free lysine, it was estimated that the additional amount of abomasal lysine required to satisfy requirements was 64 g/d in cows producing about 30 kg of milk daily. Although additional lysine above microbial and undegraded intake protein lysine flow stimulated milk protein production, conversion efficiency to milk protein lysine was low.

Six lactating Holstein cows, fitted with T-type cannulas in the proximal duodenum, were used in a replicated 3 x 3 Latin square design to determine influence of supplemental protein on amino acid profiles of duodenal chyme and plasma. Protein sources were blood meal, corn gluten meal, and cottonseed meal, which furnished approximately 46% of the total protein in corn-grain corn silage diets. Markers were 15N to estimate rumen bacteria and chromic oxide to estimate nutrient flow. Dry matter intake was lowest on blood meal. Duodenal flow of N exceeded N intake 23% on blood meal and corn gluten meal. Percentages of organic matter and protein digested in the rumen were 56.5, 41.8; 61.2, 53.4; and 50.6, 56.2 for the respective diets. Variation in patterns of amino acids flowing to the duodenum, but not in coccygeal blood, closely reflected dietary differences with six of eight essential amino acids highest for the same treatment in both diet and duodenal chyme. Essential amino acids in least abundance for milk production, measured by mammary extraction coefficients, differed among diets. We conclude that supplemental protein source influences greatly the quantity and pattern of amino acids available for digestion in lactating dairy cows.

Feeding for 150 days of 25 g per day of methionine hydroxy analog was tested on 100 cows (52 treated and 48 controls) in the Brigham Young University herd. Effect of days after parturition of initiating methionine hydroxy analog feeding also was observed. Milk yields were not affected by methionine hydroxy analog, but fat percent and fat yields were increased 21 and 17% by the additive. Abnormally low milk fat by control cows (2.84%) magnified the response to methionine hydroxy analog feeding. Feeding methionine hydroxy analog beginning 0 to 12 days postpartum elicited much larger increases of milk fat than started later (17 to 102 days). Blood from the coccygeal vein of 20 cows from each treatment had 10% more triglycerides from cows fed methionine hydroxy analog than from control cows. Increases of arterio-venous differences across the mammary gland of triglycerides and lipoproteins of blood serum suggested that increases of milk fat could have resulted from greater uptake of performed fat by the udder. Feeding methionine hydroxy analog increased methionine, isoleucine, and leucine in serum of coccygeal vein, but methionine was the only amino acid with significantly higher arteriovenous differences across the mammary gland.

Eighty-four Holstein cows in early lactation fed diets varying in protein percent (11, 14, and 17% crude protein) and degradability in the rumen (normal and heated soybean meal) were sampled for effects on amino acids and growth hormone in blood plasma, and amino acid profiles in the duodenal digesta. Essential and branched chain amino acids in plasma increased as protein and amount of protected protein in the diet increased. These changes were accompanied by decreased concentrations of nonessential amino acids. Plasma growth hormone was highest at low protein (11.3%) probably because of decreased intakes on this diet. Molar percentages of amino acids in duodenal contents were not affected by diet suggesting that our heat-treated soybean meal influenced quantity more than quality of amino acids available for absorption in the small intestines.