Identical thermal stress coupled with different temperature and humidity combinations affects nutrient digestibility and gut metabolites of laying hens

ABSTRACT The present study investigated whether the same temperature-humidity index (THI) values under different conditions of air temperature and relative humidity (RH) would affect the thermoregulatory, nutritional, and behavioral responses of laying hens. One hundred twenty Hy-Line Brown laying hens (60-weeks-old) were divided equally in two environmental chambers: 26 °C with 70% RH (hRH75) and 30 °C with 30% RH (hT75) for 28 days. The two ambient environments (hRH75 and hT75) had an identical THI value of 75, calculated using an empirical formula for laying hens. Neither hRH75 nor hT75 affected rectal and body-surface temperatures and heart and respiratory rates. The concentration of volatile fatty acids in fecal excreta were altered by the thermal treatments. hT75 vs. hRH75 decreased the proportion of acetate and increased the proportion of propionate in fecal samples. hT75 vs. hRH75 lowered the digestibility of dry matter, crude protein, and neutral detergent fiber at 14 days. Thermal treatments did not affect heat stress-associated behavioral responses including feeding, drinking, panting, and wing elevation at any stage. Laying hens exposed to the same THI at different temperatures and RH exhibit equal physiological responses including rectal and body-surface temperatures, heart and respiratory rates, and behavioral responses. Nonetheless, high-temperature treatment (hT75; 30 °C and 30% RH) vs. low temperature treatment (hRH75; 26 °C and 70% RH) affects nutrient digestibility and gut metabolites, suggesting that there are negligible but discernable responses to temperature in the gut physiology.

摘要 本研究旨在探究：在空气温度与相对湿度（Relative Humidity, RH）不同的条件下，相同的温湿度指数（Temperature-Humidity Index, THI）是否会对蛋鸡的体温调节、营养代谢及行为反应产生影响。选取120只60周龄的海兰褐（Hy-Line Brown）蛋鸡，平均分为两组，分别置于两个环境舱中饲养28天：一组为26℃、70%相对湿度（记为hRH75），另一组为30℃、30%相对湿度（记为hT75）。两组环境的温湿度指数经蛋鸡专用经验公式计算后，均为75。两组环境均未对蛋鸡的直肠温度、体表温度、心率及呼吸频率产生显著影响。热应激处理可改变粪便中挥发性脂肪酸的浓度：相较于hRH75组，hT75组蛋鸡粪便中乙酸盐占比降低，而丙酸盐占比升高。饲养至第14天时，相较于hRH75组，hT75组蛋鸡的干物质、粗蛋白质及中性洗涤纤维消化率均有所下降。各饲养阶段的热应激处理均未影响蛋鸡与热应激相关的行为反应，包括采食、饮水、喘息及翼部伸展。在温湿度指数相同但温度与相对湿度不同的环境中饲养的蛋鸡，其生理反应（包括直肠温度、体表温度、心率、呼吸频率及行为反应）并无显著差异。然而，相较于低温处理组（hRH75：26℃、70%相对湿度），高温处理组（hT75：30℃、30%相对湿度）会对蛋鸡的营养物质消化率及肠道代谢物产生影响，这表明肠道生理对温度存在虽微弱但可被检测到的响应。