Natural Thermal Conditioning and Heat Acclimation Improves Heat Tolerance in Layer Chickens During Hot-Dry Season

The aim of this study was to compare the heat tolerance of layer chickens exposed to the hot season during both chick brooding (natural thermal conditioning) and laying (heat acclimation), and that of layers exposed to the hot season only during growth phase. At the beginning of the hot season, 40 layer chickens were randomly selected and classified as Exposed (previously exposed to the hot-dry season during brooding and laying; n=20) and Novel (never exposed to the hot-dry season during brooding and laying; n=20). The results revealed that both morning and afternoon cloacal temperatures were significantly higher (P<0.05) at the beginning than peak of the hot-dry in the Novel layers and were also significantly higher in Novel than Exposed layers in the beginning of the hot-dry season. Significantly higher morning respiratory rate was observed in Novel than Exposed group at the peak of the hot-dry season. It was concluded that scheduling the stocking of day-old chicks such that brooding is done at the peak of the tropical hot season and hens have early exposure to the hot season during laying period, could marked enhance thermal conditioning and acclimation to improve heat tolerance and productivity during heat stress. Keywords: Layer Chickens, Heat stress, day-old chicks, Cloacal temperature, Heat tolerance