Department of Animal Sciences, University of Florida, Gainesville, FL 32611, USA.
Department of Animal and Dairy Sciences, University of Wisconsin, Madison, WI 53706, USA.
Reprod Fertil Dev. 2022 Dec;35(2):106-117. doi: 10.1071/RD22209.
The final weeks of gestation represent a critical period for dairy cows that can determine the success of the subsequent lactation. Many physiological changes take place and additional exogenous stressors can alter the success of the transition into lactation. Moreover, this phase is pivotal for the final stage of intrauterine development of the fetus, which can have negative long-lasting postnatal effects. Heat stress is widely recognised as a threat to dairy cattle welfare, health, and productivity. Specifically, late gestation heat stress impairs the dam's productivity by undermining mammary gland remodelling during the dry period and altering metabolic and immune responses in early lactation. Heat stress also affects placental development and function, with relevant consequences on fetal development and programming. In utero heat stressed newborns have reduced birth weight, growth, and compromised passive immune transfer. Moreover, the liver and mammary DNA of in utero heat stressed calves show a clear divergence in the pattern of methylation relative to that of in utero cooled calves. These alterations in gene regulation might result in depressed immune function, as well as altered thermoregulation, hepatic metabolism, and mammary development jeopardising their survival in the herd and productivity. Furthermore, late gestation heat stress appears to exert multigenerational effects, influencing milk yield and survival up to the third generation.
妊娠的最后几周是奶牛的关键时期，这可能决定随后泌乳的成功。许多生理变化发生，额外的外源应激可以改变泌乳的成功过渡。此外，这一阶段对胎儿子宫内发育的最后阶段至关重要，这可能对产后产生负面影响。热应激被广泛认为是对奶牛福利、健康和生产力的威胁。具体来说，妊娠后期的热应激通过破坏干奶期乳腺重塑和改变泌乳早期的代谢和免疫反应来损害母体的生产力。热应激还会影响胎盘的发育和功能，对胎儿的发育和编程产生相关影响。宫内受热应激的新生牛体重减轻、生长不良，被动免疫转移受损。此外，宫内受热应激的小牛的肝脏和乳腺 DNA 相对于宫内冷却的小牛，其甲基化模式明显不同。这些基因调控的改变可能导致免疫功能下降，以及体温调节、肝脏代谢和乳腺发育受损，危及它们在牛群中的生存和生产力。此外，妊娠后期的热应激似乎会产生多代效应，影响产奶量和存活率，甚至影响到第三代。
