Protein and energy affect splanchnic and mammary metabolisms and drive amino acid use in dairy cows

Balancing rations for essential amino acids (AA) to improve efficiency of utilisation (Eff) of N requires a better knowledge of AA use by different tissues under various nutritional conditions. Effects of infusion of AA (AAinf) and glucose (Glcinf), in a 2×2 factorial arrangement, were tested using 5 cows in a 4×4 Latin Square plus one cow. At the end of each period, splanchnic, mammary and other peripheral tissue metabolisms of AA were measured. There was no AAinf×Glcinf interaction on most of the measured parameters. Milk protein yield (MPY) increased with AAinf and Glcinf. With AAinf, catabolism by portal-drained viscera (PDV) and mammary gland of group 2 AA (Ile, Leu, Lys, and Val) increased leading to a decreased Eff. In contrast, with Glcinf, liver removal of His + Met + Phe (HMP) decreased, improving their Eff.