Evaporative cooling of ventral regions of the skin in heat-stressed laying hens

Laying hens held in battery cages in naturally ventilated poultry houses in hot countries usually develop hyperthermia, which adversely affects their performance. The present means of cooling alleviate to some degree, but cannot eliminate, the stress imposed by heat. A new approach to cooling of laying hens was developed, based on wetting the skin and promoting evaporation of water from the ventral regions of the bird. The type of plumage in the ventral regions and the exposed skin of the apteria enable more efficient wetting than is possible with dorsal cooling. A ventral cooling regime, comprising an initial period of frequent wettings followed by intermittent wetting for 10 s every 30 min was able to maintain normothermia of laying hens subjected to a 10-h period of heat exposure. Dorsal cooling was less efficient; body temperature and respiration rate were higher and skin temperatures were lower than in ventrally cooled hens. During 10 d of heat exposure, ventrally cooled hens maintained egg weight and shell index (mg/cm²), whereas their food intake decreased moderately. In contrast, egg weight, shell index, and food intake all decreased markedly in uncooled or dorsally cooled hens. Transient alterations in plasma concentrations of corticosterone, progesterone, and estradiol were noted in uncooled and dorsally cooled hens but not in ventrally cooled hens. Results indicate that ventral cooling is an efficient method to alleviate heat stress in laying hens during summer. Successful implementation of ventral cooling in poultry houses will depend on optimal installation of sprinklers and on minimal wetting of manure.