Abstract: In this study, plasma 3-Methylhistidine (3-MH) and other Amino Acids (AA) were measured in high yielding dairy cows between 1 week prepartum and 4 weeks postpartum to evaluate the effect of different protein levels in a postpartum diet on milk performance, metabolites and feed intake. Eleven multiparous cows were used in the study and all received the same prepartum diet. Postpartum, they were divided into two groups; five cows received a diet of 19% CP (CP19) and six cows received a diet of 17% CP (CP17). Plasma 3-MH and also other AA concentrations were significantly lower in the CP19 cows than in the CP17 cows. The peak plasma 3-MH concentration postpartum in CP17 and CP19 were 15.5 and 9.9 μM, respectively while the mean plasma 3-MH concentration throughout the trial in CP17 and CP19 were 11.7 and 7.6 μM, respectively. Milk yield and composition tended to improve in CP19 cows, however, these were not significant. Blood Urea Nitrogen (BUN) was significantly higher in CP19 than that in CP17 (14.3 vs. 9.9 mg dL-1, respectively). The kinetics of plasma 3-MH were the same as a earlier study where it increased after parturition for 1 week and then progressively decreased until 4 weeks postpartum. These results indicate that muscle protein mobilization can be lowered by protein in the diet as evidenced by plasma 3-MH. Lower AA might be an indication of their efficient utilization from the diet, so that an increased consumption of AA for milk production is reflected in lower AA levels in blood. This study suggested that even for cows receiving 19% CP in early lactation, if the AA utilization into milk protein is efficient, BUN can be kept within a normal range. In conclusion, plasma 3-MH is a sensitive and useful index for protein nutrition in early lactation and a 19% CP diet might be effective in preventing body protein degradation as evidenced by plasma 3-MH.
K. Sawada, K. Nagano and N. Nishino, 2013. Plasma 3-Methylhistidine Concentration in Peripartum Dairy Cows Given Diets with Two Protein Levels. Journal of Animal and Veterinary Advances, 12: 712-717.