Short communication: Postpartum plasma amino acid concentration in primi- and multiparous Holstein cows

A better understanding of changes in plasma amino acid (AA) concentrations during the transition period may help optimize nutrition to improve health, welfare, and production in dairy cows. The aim of this study was to assess changes in plasma AA during the transition period in Holstein cows and first-lactation heifers. Blood samples for AA analysis were collected from the tail vein/artery of 9 multi- and 8 primiparous cows 3 weeks prior to and at weeks 1, 2, and 3 post-calving. Concentration of the sum of essential AA (EAA) was similar between primiparous and multiparous cows before calving but was 17.0% lower in multiparous vs. primiparous cows postpartum, which was related to both greater milk production and imbalance in estimated metabolizable protein supply vs. demand in the multiparous group of cows. In both parity groups, EAA concentrations declined by 20.0% from week 1 to week 3 postpartum. The sum of non-essential protein and non-protein AA increased linearly in the weeks after calving and was similar between primi- and multiparous cows. Compared with prepartum, plasma His concentration decreased 13.1% postpartum in both primiparous and multiparous cows but primiparous cows had 7.6% greater plasma His concentration than multiparous cows pre- and postpartum. Methionine and Lys concentrations were not affected by parity, but concentrations of both AA decreased (22.0% and 24.5%, respectively) after calving. Overall, plasma concentration of EAA decreased after calving, indicating a negative EAA balance (supply vs. demand) around parturition. Lower postpartum plasma concentrations of EAA in multiparous cows likely reflect an overall negative EAA balance due to decreased supply and increased demand to sustain greater milk production, compared with primiparous cows.