Effect of incubational thermal manipulation on the embryonic and early post-hatch growth in layer chickens

A study was undertaken to investigate the role of hot or cold temperature stress during incubation period of layer chicken egg and their effects on hatchability, embryo viability, post-hatch growth and development of vital organs in layer chicks. Fertile eggs of CARI Sonali (n=300) were set in a force draft incubator at temperature of 37.5°C and 60% relative humidity (RH) for 14 days. On 15^th day of incubation, 100 eggs were incubated at low temperature (36.0°C, RH 60%), another 100 eggs at high temperature (39.0°C, RH 70%) and rest 100 eggs (control) were kept in the same incubator. On 19^th days the eggs from the respective group were transferred to pedigree hatching boxes and provided hatching temperature of 37.25°C and RH 65% till hatching of the eggs. Following hatching, the chicks were reared in battery brooders with standard brooding temperature (32.0°C) till 10 days, then each group was subjected to cold (24.0°C), hot (35.0°C) or standard brooding temperature (29.5°C) until 21 days of age. The cold incubated eggs had 91% hatchability compared to 86.0 and 84.0% hatchability in hot or standard incubated eggs. Though there was no difference in chick weight or egg weight but their ratio was significantly higher (P<0.01) in cold incubated group compared to standard incubated group. On the day of hatch, cold incubated chicks had significantly lower body temperature but higher bursa weight than hot or standard incubated chicks. 10^th day body weight and weight gain during first 10 days was significantly higher (P<0.01) in hot or standard incubated chicks. However, when exposed to cold or hot brooding temperature, cold incubated chicks had significantly higher (P<0.01) weight gain during 11–21 days of age, and better ND vaccine response but significantly lower (P<0.01) body temperature. It is concluded that incubational temperature of 36.0°C and 60% RH maintained during 15–19^th day of incubation in laying chicken eggs can improve the hatchability, post-hatch growth, immunity and the ability to withstand thermal stress during brooding period.