Department of Animal and Poultry Nutrition, Faculty of Animal Science, Gorgan University of Agriculture Science and Natural Resources, Gorgan 49138-15739, Iran.
Department of Animal and Poultry Nutrition, Faculty of Animal Science, Gorgan University of Agriculture Science and Natural Resources, Gorgan 49138-15739, Iran.
J Dairy Sci. 2021 Feb;104(2):1744-1758. doi: 10.3168/jds.2020-19115. Epub 2020 Dec 11.
The objective of this study was to differentiate the effects of acute heat stress (HS) from those of decreased dry matter intake (DMI) during the prepartum period on metabolism, colostrum, and subsequent production of dairy cows. Holstein dairy cows (n = 30) with similar parity and body weight were randomly assigned to 1 of 3 treatments on 45 d before calving: (1) cooled (CL, n = 10) conditions with ad libitum feed intake, (2) HS conditions with ad libitum feed intake (n = 10), and (3) pair-fed cooled (CLPF, n = 10) with reduced DMI similar to the HS group while housed under cooled conditions. The reduction in the amount of feed offered to the CLPF cows was calculated daily as the percentage decrease from the average DMI of HS cows relative to the CL cows. For CLPF and CL cows, barns provided shade, sprinklers, and fans, whereas the HS cows were provided only with shade. Cows in all groups received individually the same total mixed ration. Cows were dried off 60 d before the expected calving. Cows in the HS group and, by design, the CLPF cows had reduced DMI (~20%) during the experiment. Heat stress decreased gestation length, first colostrum yield, and calf birth weight compared with CL and CLPF cows. Milk yield decreased 21% (5 kg) in the HS and 8% (2 kg) in CLPF cows, indicating that reduced feed intake during late gestation accounted for 60% of the total reduced milk yield. The CLPF cows exhibited an elevated NEFA concentration compared with the CL and HS cows. The HS cows had a greater mRNA abundance of HSP70 in the peripheral blood leukocytes at 21 d prepartum compared with the other groups. At calving, the mRNA abundance of HSP70 was greater in HS cows, followed by CLPF, compared with the CL cows. In conclusion, HS during the late gestation period caused metabolism and production differences, which were only partially attributed to reduced feed intake in dairy cows.
本研究旨在区分产前阶段急性热应激（HS）与干物质采食量（DMI）减少对奶牛代谢、初乳和随后生产性能的影响。选择具有相似胎次和体重的荷斯坦奶牛（n = 30），在产前 45 d 时随机分为 3 种处理组之一：（1）自由采食冷却（CL）组（n = 10），（2）自由采食 HS 组（n = 10），和（3）冷却条件下的限饲 CLPF 组（n = 10），其 DMI 减少量与 HS 组相似，但在冷却条件下饲养。CLPF 奶牛的饲料减少量每天根据 HS 奶牛相对于 CL 奶牛的平均 DMI 减少百分比计算。对于 CLPF 和 CL 奶牛，牛舍提供遮阳、喷淋和风扇，而 HS 奶牛仅提供遮阳。所有组的奶牛均接受相同的全混合日粮。奶牛在预期分娩前 60 d 停奶。HS 组和设计的 CLPF 奶牛在实验期间 DMI 减少（~20%）。与 CL 和 CLPF 奶牛相比，HS 降低了妊娠长度、初乳产量和犊牛初生重。HS 和 CLPF 奶牛的产奶量分别减少 21%（5 kg）和 8%（2 kg），表明妊娠后期减少的采食量占总产奶量减少的 60%。与 CL 和 HS 奶牛相比，CLPF 奶牛的 NEFA 浓度升高。与其他组相比，HS 奶牛在产前 21 d 外周血白细胞中 HSP70 的 mRNA 丰度更高。在分娩时，HS 奶牛的 HSP70 mRNA 丰度高于 CLPF 奶牛，其次是 CL 奶牛。总之，妊娠后期的 HS 导致了奶牛代谢和生产性能的差异，这些差异仅部分归因于奶牛采食量的减少。
