Milk protein responses to balanced amino acid and removal of L eucine and A rginine supplied from jugular‐infused amino acid mixture in lactating dairy cows

• Published in: Journal of animal physiology and animal nutrition 2017-10, Vol.101 (5)
• Main Authors: Tian, W., Wang, H. R., Wu, T. Y., Ding, L. Y., Zhao, R., Khas, E., Wang, C. F., Zhang, F. Q., Mi, F. Y., Wang, L., Ning, L. T.
• Format: Article
• Language: English
• ISSN: 0931-2439; 1439-0396
• DOI: 10.1111/jpn.12603

This study was undertaken to evaluate the milk protein response when cows were supplied a balanced AA profile and to determine whether a deficiency of Leucine (Leu) or Arginine (Arg) had a negative effect on milk protein. Eight mid‐lactation Holstein cows were randomly assigned to 5‐day continuous jugular infusions of saline ( CTL ), EAA mixture prepared on the profile of casein and supplied (in % of lysine (Lys)) 100% of Lys, 33.3% of methionine (Met), 110.2% of Leu, 43.6% of Arg, 50.8% of threonine (Thr), 81.6% of valine (Val), 69.7% of isoleucine (Ile), 61.4% of phenylalanine (Phe) and 34.2% of histidine (His) ( Casein , 160 g/d), EAA mixture excluding Leu (−Leu, 163 g/d) or EAA mixture excluding Arg (−Arg, 158 g/d) in a duplicated 4 × 4 Latin square design with four infusion periods separated by 7‐day interval period. The basal diet supplied 1.6 Mcal NE L and 94.4 g MP per 1 kg DM to meet requirements for lactation. The Casein treatment provided a balanced supply (in % of MP ) of 10.3% Leu and 5.3% Arg, whereas in the two subsequent −Leu and −Arg treatments, the concentration of Leu and Arg was reduced to 8.4 and 4.6% respectively. Dry matter intake (15.4 kg/day) was not affected by treatments. The Casein treatment increased milk yield (14.9%, p   <   0.001), milk protein yield (120 g, p   <   0.001) and milk protein efficiency (0.03, p   =   0.099) than CTL treatment. However, the −Leu treatment decreased the responses of above‐measured parameters by 6.25%, 70 g, 0.05 (p   <   0.06) (compared with Casein ). These effects of Leu were related to decreased Leu concentration and improved concentration of Ile and Val in plasma. The −Arg treatment decreased the plasma Arg concentration than the Casein treatment, whereby resulted in the decrease of milk yield (5.7%, p   =   0.073), milk protein yield (60 g, p   =   0.011) and milk protein efficiency (0.04, p   =   0.037). In conclusion, supply of EAA profile of casein can increase the lactation production in dairy cows, and 8.6% of Leu in MP partly limits the milk protein response when the requirements of Lys, Met and His were met. The level of Arg at 4.6% MP is not deemed to an ideal profile, as evidenced by decreased milk protein efficiency.