Effects of Amount and Profile of Amino Acids Supply on Lactation Performance, Mammary Gland Metabolism, and Nitrogen Efficiency in Holstein Dairy Cows

To evaluate the effects of amount and profile amino acid (AA) on milk protein yield (MPY), mammary metabolism, efficiency nitrogen use (ENU), ten cows were used in 5 × replicated Latin squares fed a positive control (16.1% crude protein-CP) or two lower CP diets (14.6 13.2%) with without essential AA (EAA) infusion. The EAA solutions provided predicted limiting each treatment continuously infused into abomasum cows. Milk production MPY not affected by (mean 35.4 kg/d 1.03 kg/d, respectively). Efficiency utilization was increased as dietary decreased but infusion (p < 0.01). Energy-corrected 13.2% CP, 14.6% diet = 0.09), reaching value. Infusions affinity for non-infused (Ile, Phe, Thr, Trp), allowing same despite arterial concentrations these AA. Higher did increase their uptake 0.40; p 0.85). Mammary metabolism fully explain changes N efficiency, suggesting that it might be driven less extramammary catabolism supply reduced.