Effects of branched-chain amino acids and sodium caseinate on milk proteinconcentration and yield from dairy cows

Our study investigated the separate and combined effects of branched-chain amino acids (AA) and sodium caseinate on milk protein concentration and yie ld. Four Holstein cows (112 d in milk) were abomasally infused with water, branched-chain AA (150 g/d), sodium caseinate (600 g/d), or branched-chain AA plus sodium caseinate (44 and 600 g/d, respectively) according to a 4 x 4 Latin square design with 8-d treatment periods. Cows were fed a dry diet based on alfalfa hay and concentrates for ad libitum intake. The ration was formulated to exceed requirements for metabolizable energy and protein usi ng the Cornell Net Carbohydrate and Protein System. Neither daily dry matte r intake (24.2 +/- 0.4 kg/d; (X) over bar +/- SEM) nor milk yield (32.9 +/- ; 0.4 kg/d) was affected by any of the infusion treatments. Infusion of bra nched-chain AA had no effect on any milk production parameters, despite a 5 0% increase in their concentrations. Modest increases in milk protein conce ntration (0.1%) and milk protein yield (62 g/d) resulted from the infusion of sodium caseinate or branched-chain AA plus sodium caseinate. True protei n and whey protein concentrations in milk were also marginally increased by infusion of sodium caseinate and branched-chain AA plus sodium caseinate, and infusion of branched-chain AA, sodium caseinate, or both elevated milk nonprotein N content. Plasma urea N concentrations were elevated by the sod ium caseinate and branched-chain AA plus sodium caseinate treatments. No tr eatment effects on other plasma metabolites or hormones were observed. Our results show no benefit of supplementation with branched-chain AA and only modest effects of sodium caseinate on milk protein concentration and yield in well-fed cows.