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.
Domest Anim Endocrinol. 2020 Jul;72:106433. doi: 10.1016/j.domaniend.2019.106433. Epub 2020 Jan 2.
The objective of this study was to evaluate the effects of heat stress in late gestation independent of maternal reduced feed intake on performance, blood hormones and metabolites, and immune responses of dairy calves from birth through weaning. A total of 30 multiparous Holstein cows at 45 d before expected calving were randomly assigned to one of 3 groups: (1) thermal neutral (CL, n = 10) conditions with ad libitum feed intake (10% of refusals on an as-fed basis); (2) pair-fed thermal neutral (CLPF, n = 10) conditions to reduce feed intake to levels similar to the heat stress (HS) group while reared under thermoneutral conditions (80% of the CL group); or (3) heat stress (HS, n = 10) conditions with ad libitum feed intake. Pair-feeding was conducted to quantify the confounding effects of dissimilar feed intake. Calves (10/group) born to cows that were exposed to cooling (IU-CL), pair-feeding (IU-CLPF), or heat stress (IU-HS) were used from birth through weaning. After birth, all the calves were managed under identical conditions. IU-HS calves had lower birth weight, and hip height at birth and 14 d of age. Compared with IU-CL and IU-CLPF calves, IU-HS calves had lower serum concentration of IgG and apparent efficiency of IgG absorption but higher serum insulin concentrations. Cortisol concentration in serum was higher in IU-HS and IU-CLPF calves compared to IU-CL calves. The neutrophil percentage was lower in IU-CL calves than in IU-HS and IU-CLPF calves. Neutrophil-lymphocyte ratio was higher in IU-HS calves compared to IU-CLPF and IU-CL calves. The mRNA expression of TNFα of IU-HS calves was downregulated compared with IU-CL and IU-CLPF calves. In summary, maternal HS during late gestation reduces calf birth weight and dramatically alters blood hormones and metabolites, but its effect on immune system function was not independent of maternal reduced feed intake.
本研究旨在评估妊娠后期热应激对奶牛犊牛性能、血液激素和代谢物以及免疫反应的影响，而不考虑母体采食量减少。共有 30 头接近分娩的经产荷斯坦奶牛，在预计分娩前 45 天随机分为 3 组：（1）热中性（CL）组，自由采食（基于实际采食量，采食水平为 10%的剩料）；（2）热中性限饲（CLPF）组，采食量减少至与热应激组相似的水平，同时在热中性条件下饲养（CL 组的 80%）；（3）热应激（HS）组，自由采食。限饲是为了量化不同采食量的混杂影响。从出生到断奶，每组（10 头）出生的犊牛都用于研究。出生后，所有犊牛均在相同条件下管理。与 IU-CL 和 IU-CLPF 犊牛相比，IU-HS 犊牛出生体重和出生时以及 14 日龄时的臀部高度较低。与 IU-CL 和 IU-CLPF 犊牛相比，IU-HS 犊牛血清 IgG 浓度和 IgG 表观吸收率较低，但血清胰岛素浓度较高。与 IU-CL 犊牛相比，IU-HS 和 IU-CLPF 犊牛血清皮质醇浓度较高。与 IU-HS 和 IU-CLPF 犊牛相比，IU-CL 犊牛的中性粒细胞百分比较低。与 IU-CLPF 和 IU-CL 犊牛相比，IU-HS 犊牛的中性粒细胞-淋巴细胞比值较高。与 IU-CL 和 IU-CLPF 犊牛相比，IU-HS 犊牛的 TNFαmRNA 表达下调。综上所述，妊娠后期母体热应激降低了犊牛的出生体重，并显著改变了血液激素和代谢物，但对免疫系统功能的影响并不独立于母体采食量减少。
