热应激对不同泌乳阶段奶牛产奶性能的影响OA北大核心CSTPCD

The objective of this study was to implement appropriate prevention and cooling measures for cows at different lactation phases in hot weather and reduce the influence of heat stress on milk produc-tion performance of lactating cows.A total of 45 healthy Holstein cows at different lactation phases were selected to investigate the comprehensive effects of heat stress on dairy cows'respiratory rate,milk yield and milk composition at different lactation phases.The results showed that:(1)heat stress significantly increased the respiratory rate of dairy cows at different lactation phases(P＜0.05),with a greater effect on the respiratory rate of dairy cows at early lactation phase.(2)Under heat stress,the milk yield of dairy cows at all lactation phases decreased significantly(P＜0.05).The milk yield of dairy cows at early lacta-tion phase decreased by 18.58％,being the largest among dairy cows at different lactation phases.(3)There were no significant changes in milk fat and milk protein contents under heat stress(P＞0.05),while non-fat solids,lactose and casein contents significantly increased during early lactation(P＜0.05).In con-clusion,heat stress exerts greater impacts on milk production performance in early lactation cows,and more attention should be paid to preventing and coping with the occurrence of heat stress in dairy cows in early lactation phase.