Department of Animal Sciences, North Carolina Agricultural and Technical State University, Greensboro, North Carolina, United States of America.
Department of Animal Sciences, Purdue University, West Lafayette, Indiana, United States of America.
PLoS One. 2024 Oct 31;19(10):e0310787. doi: 10.1371/journal.pone.0310787. eCollection 2024.
Heat stress (HS) exerts detrimental effects on animal production, with lactating sows being particularly vulnerable. Understanding the mechanisms involved in HS response could aid in developing effective strategies against the negative impacts on livestock. Recent genome wide association studies identified two core circadian clock genes as potential candidates in mediating HS response. The study aimed to investigate how cooling lactating sows under natural heat stress conditions impacted circadian patterns of respiration rate (RR), rectal temperature (RT), behavior, salivary melatonin and cortisol levels, and diurnal patterns of cytokines in saliva. Mixed parity lactating sows were assigned to one of two treatment groups: electronic cooling pad (C; n = 9) and heat-stressed (H; n = 9). The experiment spanned two 48 h periods of elevated ambient temperatures due to summer heat wave. In the first 48 h period, RR was recorded every 30 min, RT every 60 min, and behaviors (eating, standing, sitting, laying, sleeping, drinking, and nursing) every 5 min. In the second 48 h period, saliva samples were collected every 4 h. Cooling reduced RR and RT and altered circadian patterns (P < 0.05). Cooling did not affect amount of time engaged in any behavior over the 48 h period (P > 0.05), however, daily patterns of eating, standing and laying differed between the treatments (P < 0.05), with altered eating behavior related to RT increment in H sows (P < 0.05). Cooling increased and altered the circadian pattern of salivary melatonin (P < 0.05). Cooling also influenced the diurnal pattern of saliva cytokines. Cooling had no impact on saliva cortisol levels. In conclusion, cooling HS sows impacted circadian rhythms of physiology and behavior, supporting the need for further research to understand if circadian disruption underlies decreased production efficiency of HS animals.
热应激（HS）对动物生产有不利影响，哺乳期母猪尤其易受影响。了解 HS 反应的机制有助于制定针对家畜负面影响的有效策略。最近的全基因组关联研究确定了两个核心生物钟基因作为介导 HS 反应的潜在候选基因。本研究旨在探讨在自然热应激条件下冷却哺乳期母猪如何影响呼吸率（RR）、直肠温度（RT）、行为、唾液褪黑素和皮质醇水平的昼夜节律以及唾液中细胞因子的昼夜节律。混合胎次哺乳期母猪被分配到以下两个处理组之一：电子冷却垫（C；n = 9）和热应激（H；n = 9）。实验跨越了两个由于夏季热浪导致环境温度升高的 48 小时周期。在第一个 48 小时周期中，RR 每 30 分钟记录一次，RT 每 60 分钟记录一次，行为（进食、站立、坐、躺、睡、饮水和哺乳）每 5 分钟记录一次。在第二个 48 小时周期中，每 4 小时收集一次唾液样本。冷却降低了 RR 和 RT，并改变了昼夜节律模式（P < 0.05）。冷却对 48 小时内任何行为的总时间没有影响（P > 0.05），但是，两种处理之间的进食、站立和躺卧的日变化模式不同（P < 0.05），与 H 母猪 RT 增加相关的是改变的进食行为（P < 0.05）。冷却增加并改变了唾液褪黑素的昼夜节律模式（P < 0.05）。冷却还影响了唾液细胞因子的日变化模式。冷却对唾液皮质醇水平没有影响。总之，冷却 HS 母猪会影响生理和行为的昼夜节律，这支持了进一步研究以了解 HS 动物生产效率下降是否与昼夜节律紊乱有关的必要性。
