[目的]探究热应激条件下临沂地区不同泌乳阶段奶牛的生产性能、乳成分及血液生化指标的变化特征。[方法]选取24 头健康荷斯坦牛,按泌乳天数分为早期（≤60 d）、中期（61~150 d）和晚期（≥151 d）三组,于2024年5—8月进行试验,监测非热应激期与热应激期奶牛的产奶量、呼吸频率、直肠温度、乳成分及血液指标（HSP70、催乳素、瘦素）。[结果]热应激显著降低各泌乳阶段奶牛的产奶量（P<0.05）,并导致呼吸频率和直肠温度显著升高。泌乳早期和中期奶牛的乳糖与固形物含量显著增加（P<0.05）,而乳脂肪率和乳蛋白率无显著变化。热应激还显著上调HSP70表达,并降低泌乳早期和中期奶牛的催乳素水平（P<0.05）,瘦素水平变化不显著。[结论]热应激对奶牛生产性能、乳品质和血液指标均有显著影响,泌乳早期和中期奶牛更为敏感。研究结果为制定区域性奶牛热应激防控策略提供了理论依据。
[Objective] This study aimed to investigate the effects of heat stress on production performance, milk composition,and blood biochemical indicators of dairy cows in different lactation stages in the Linyi region. [Methods] A total of 24 healthy Holstein cows were selected and divided into three groups according to days in milk: early lactation （≤60 d）, mid-lactation （61~150 d）,and late lactation （≥151 d）. The experiment was conducted from May to August 2024. Milk yield,respiratory rate,rectal temperature,milk composition,and blood indicators （HSP70,prolactin,leptin） were monitored during non-heat stress and heat stress periods. [Results] Heat stress significantly reduced milk yield in all lactation stages （P< 0.05） and significantly increased respiratory rate and rectal temperature. The lactose and solid content increased significantly in early and mid-lactation cows （P< 0.05）,while milk fat rate and milk protein rate showed no significant changes. Heat stress also significantly up-regulated HSP70 expression and reduced prolactin levels in early and mid-lactation cows （P< 0.05）,with no significant change in leptin levels. [Conclusion] Heat stress significantly affects the production performance,milk quality,and blood indicators of dairy cows,with early and mid-lactation cows being more susceptible. The results provide a theoretical basis for developing regional strategies for the prevention and control of heat stress in dairy cows.
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