Heat stress (HS) mitigation strategies are critically needed to combat the substantial economic effects on animal agriculture. The manifestations of seasonal infertility include delayed puberty onset, reduced conception rates, decreased litter size, and increased wean to estrus interval. To assess the effects of HS during early gestation and evaluate the benefit of supplemental altrenogest (ALT) as a mitigation strategy, 30 crossbred postpubertal gilts (157 ± 11 kg body weight) were subjected to estrous synchronization via 14 d oral administration of ALT. Artificial insemination during estrus was performed, and gilts were then placed into one of four treatment groups: HS (35 ± 1 °C for 12 h/31.60 ± 1 °C for 12 h) with (HSALT, n = 7) or without (HSCON, n = 7) 15 mg/d ALT supplementation or thermal neutral (TN; 20 ± 1 °C) conditions with (TNALT, n = 8) or without (TNCON, n = 8) 15 mg/d ALT supplementation until 12 d post-estrus (dpe). Administrating ALT occurred at 0600 hours from 3 to 12 dpe, and rectal temperatures (TR) and respiration rates (RR) were recorded. Blood was collected via jugular venipuncture on 0, 4, 8, and 12 dpe. Gilts were euthanized humanely at 12 dpe followed by the collection of ovarian tissue, and uterine flushing for conceptus collection. In HS compared with TN gilts, RR and TR were increased (P < 0.01) but unaffected by ALT supplementation. Feed intake was reduced (P < 0.01) by HS but unaltered by the ALT treatment. Corpora lutea (CL) weight was reduced (P < 0.01) in HSCON gilts when compared with TNCON and HSALT gilts despite progesterone concentrations in serum and luteal tissue not being affected by treatment (P ≥ 0.10). CL diameter was reduced (P ≤ 0.05) in HSALT gilts compared with other treatments. Interleukin-1β (IL1B) uterine flush concentration was not affected (P > 0.20) by environment or ALT supplementation, although moderate (P = 0.06) interaction between environment and ALT existed, as IL1B concentration in TNALT was increased (P = 0.03) compared with TNCON gilts. While environment did not affect conceptus development (P = 0.90), ALT supplementation advanced conceptus elongation (P < 0.01). Collectively, these data demonstrate that HS may affect luteal development before pregnancy establishment, and ALT increases conceptus elongation by 12 dpe.

中文翻译：

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后备母猪怀孕前环境温度升高和补充阿曲诺孕素的影响

迫切需要缓解热应激 (HS) 的策略来应对对畜牧业的重大经济影响。季节性不孕症的表现包括青春期开始延迟、受孕率降低、产仔数减少以及断奶至发情间隔增加。为了评估 HS 在妊娠早期的影响并评估补充 altrenogest (ALT) 作为缓解策略的益处，通过 14 天的 ALT 口服给药，对 30 头杂交的青春期后后备母猪（157 ± 11 kg 体重）进行了发情同步。在发情期间进行人工授精，然后将后备母猪放入四个处理组之一：HS（35 ± 1 °C 12 小时/31.60 ± 1 °C 12 小时）有（HSALT，n = 7）或没有（ HSCON, n = 7) 15 mg/d ALT 补充或热中性 (TN; 20 ± 1 °C) 条件下 (TNALT, n = 8) 或不补充 (TNCON, n = 8) 15 mg/d ALT 补充剂直至发情后 12 天 (dpe)。在 3 至 12 dpe 的 0600 小时内进行 ALT 给药，并记录直肠温度 (TR) 和呼吸频率 (RR)。在 0、4、8 和 12 dpe 通过颈静脉穿刺收集血液。后备母猪在 12 dpe 时被人道地安乐死，然后收集卵巢组织，并冲洗子宫以收集孕体。HS 与 TN 后备母猪相比，RR 和 TR 增加（P < 0.01），但不受 ALT 补充的影响。HS降低了采食量（P＜0.01），但ALT处理没有改变。与 TNCON 和 HSALT 后备母猪相比，HSCON 后备母猪的黄体 (CL) 体重降低 (P < 0.01)，尽管血清和黄体组织中的孕酮浓度不受治疗影响 (P ≥ 0.10)。与其他处理相比，HSALT 后备母猪的 CL 直径减小 (P ≤ 0.05)。白细胞介素-1β (IL1B) 子宫冲洗浓度不受环境或 ALT 补充的影响 (P > 0.20)，尽管环境与 ALT 之间存在中度 (P = 0.06) 相互作用，因为 TNALT 中的 IL1B 浓度增加 (P = 0.03)与 TNCON 后备母猪相比。虽然环境不影响胎体发育（P = 0.90），但补充 ALT 可促进胎体伸长（P < 0.01）。总的来说，这些数据表明 HS 可能会影响妊娠建立前的黄体发育，并且 ALT 可使孕体伸长增加 12 dpe。尽管环境和 ALT 之间存在中度（P = 0.06）相互作用，但与 TNCON 后备母猪相比，TNALT 中的 IL1B 浓度增加（P = 0.03）。虽然环境不影响胎体发育（P = 0.90），但补充 ALT 可促进胎体伸长（P < 0.01）。总的来说，这些数据表明 HS 可能会影响妊娠建立前的黄体发育，并且 ALT 可使孕体伸长增加 12 dpe。尽管环境和 ALT 之间存在中度（P = 0.06）相互作用，但与 TNCON 后备母猪相比，TNALT 中的 IL1B 浓度增加（P = 0.03）。虽然环境不影响胎体发育（P = 0.90），但补充 ALT 可促进胎体伸长（P < 0.01）。总的来说，这些数据表明 HS 可能会影响妊娠建立前的黄体发育，并且 ALT 可使孕体伸长增加 12 dpe。