N-羟甲基蛋氨酸钙对泌乳奶牛产奶量、乳成分和血清生化指标的影响

The objective of this study was to determine the optimal supplemental level of N-hydroxymethyl-DL-methionineCa（N-HMM-Ca） in diets for lactating Holstein dairy cows. Thrity healthy Holstein dairy cows, similarly in milk yield, days in lactation and parity, were allocated into five groups in a randomized complete block design with six cows per group. Cows were supplemented with N-HMM-Ca at 0g (control group),22.5g,45g,112.5g,225g in the basal diet. The pre-experimental period lasted for 14 days, and the experimental period lasted for 42 days. The results showed that: milk yield were the highest in 22.5g group, and significant higher than control group(P<0.05).Milk fat percentage and milk total solids percentage were no significant differences with the control group (P >0.05),the level of 22.5-112.5g/d N-HMM-Ca adding were remained stable under hot and humid environments. In 42 days,milk protein percentage was increased 3.82%,6.37%,11.47% ,-1.27% than control group, respectively; MUN and BUN concentrations were appear downtrend (P>0.05) . Cows fed 225g/d of N-HMM-Ca had lower milk fat, protein, total solids and MUN concentration than did cows in the control group(P>0.05) ; GLU concentrations were increased and HDL was decreased than control group ,significantly(P <0.05).In conclusion, the appropriate dosage of adding N-HMM-Ca into Chinese Holston dairy cows' feedstuffs is 22.5-112.5g per day.