Physiological Responses to Heat Stress in Laying Hens Managed Under Open-Sided Housing in Ogun State, South West Nigeria

Heat stress is a major constraint on poultry production in tropical West Africa, reducing egg output, feed efficiency, and overall physiological performance. This study examined physiological responses to heat stress in Isa Brown laying hens maintained under open-sided housing at a commercial farm in Ogun State, South West Nigeria. One hundred and twenty layers at thirty weeks of age were monitored during the hot-dry season across an eight-week period. Rectal temperature, respiratory rate, water intake, feed intake, egg production percentage, and serum corticosterone were measured weekly. Ambient temperature and humidity were recorded continuously using data loggers. Significant positive correlations were established between ambient temperature and rectal temperature, respiratory rate, water intake, and serum corticosterone, while negative correlations were observed for feed intake and egg production. Mean serum corticosterone was 28% higher during peak heat weeks compared to moderate-temperature periods. Panting was the predominant thermoregulatory behaviour observed. Feed intake depression during peak heat events averaged 18% relative to comfortable temperature periods. These findings underscore the significant physiological burden imposed by tropical heat on commercial layers and support the implementation of heat mitigation strategies including dietary electrolyte supplementation and housing orientation modifications in South West Nigeria. Keywords: heat stress, laying hens, serum corticosterone, thermoregulation, South West Nigeria.