Department of Animal Science, Iowa State University, Ames, IA.
J Anim Sci. 2019 Oct 3;97(10):4314-4322. doi: 10.1093/jas/skz251.
Heat stress (HS) occurs when heat dissipation mechanisms are insufficient to maintain euthermia, and it is associated with seasonal infertility (SI), which manifests as smaller litters, longer wean-to-estrus interval, increased abortions, and reduced conception rates. To understand HS-induced mechanisms underlying SI, crossbred post-pubertal gilts (167 ± 10 kg; n = 14) experienced either thermal neutral (TN, 20 ± 1 °C, n = 7) or cyclical HS (35 ± 1 °C for 12 h and 31.6 °C for 12 h, n = 7) conditions from 2 to 12 d post-estrus (dpe). Estrous cycles were synchronized via altrenogest administration for 14 d, phenotypic manifestation of estrus was observed and gilts were assigned to experimental treatment. Gilts were limit fed 2.7 kg daily with ad libitum water access. Blood was collected at 0, 4, 8, and 12 dpe via jugular venipuncture and animals were humanely euthanized at 12 dpe. The corpora lutea (CL) width were measured via digital calipers on both ovaries, and CL from one ovary were excised, weighed, and protein and steroid abundance analyzed via western blotting and ELISA, respectively. Relative to TN, HS increased (P < 0.01) rectal temperature and respiration rates and reduced (P < 0.01) feed intake. The CL from HS ovaries were reduced in diameter (P < 0.05) and weight (P < 0.01) relative to those from TN animals. No difference (P = 0.38) in CL or serum progesterone concentrations between groups was observed at any time point, though at 12 dpe the serum progesterone:CL weight was increased (P < 0.10) by HS. No treatment differences (P = 0.84) in circulating insulin were observed. Luteal protein abundance of steroid acute regulatory protein, 3 beta-hydroxysteroid, or prostaglandin F2α receptor were not different between treatments (P = 0.73). Taken together, these data demonstrate that the CL mass is HS sensitive, but this phenotype does not appear to be explained by the metrics evaluated herein. Regardless, HS-induced decreased CL size may have important implications to pig SI and warrants additional attention.
热应激（HS）发生在散热机制不足以维持体温正常时，与季节性不孕（SI）有关，表现为产仔数减少、断奶至发情间隔时间延长、流产增加和受孕率降低。为了了解 HS 引起 SI 的机制，杂交后备母猪（167±10kg；n=14）在发情后 2 至 12 天（dpe）分别经历热中性（TN，20±1°C，n=7）或周期性 HS（35±1°C 持续 12 小时和 31.6°C 持续 12 小时，n=7）条件。发情周期通过给予阿尔特罗雌酮（altrenogest）14 天同步化，观察发情表现，并将母猪分配到实验处理中。母猪每天限量喂食 2.7kg，自由饮水。通过颈静脉穿刺在发情后 0、4、8 和 12 天采集血液，12 天对动物进行人道安乐死。通过数字卡尺测量双侧卵巢上的黄体（CL）宽度，并从一侧卵巢切除 CL，称重，并通过 Western 印迹和 ELISA 分别分析蛋白质和类固醇丰度。与 TN 相比，HS 增加了（P<0.01）直肠温度和呼吸率，并降低了（P<0.01）采食量。HS 卵巢的 CL 直径（P<0.05）和重量（P<0.01）均小于 TN 动物。在任何时间点，两组间 CL 或血清孕酮浓度均无差异（P=0.38），但在 12 天，HS 增加了血清孕酮：CL 重量（P<0.10）。循环胰岛素无处理差异（P=0.84）。类固醇急性调节蛋白、3β-羟甾酮或前列腺素 F2α 受体的黄体蛋白丰度在处理之间无差异（P=0.73）。综上所述，这些数据表明 CL 质量对 HS 敏感，但这种表型似乎不能用本文评估的指标来解释。无论如何，HS 引起的 CL 大小减小可能对猪 SI 有重要影响，值得进一步关注。
