Histological and histochemical evaluations on the effects of high incubation temperature on the embryonic development of tibial growth plate in broiler chickens.

The effects of experimentally induced high incubation temperature on the embryonic development of growth plate of the chicken were investigated by means of histological and enzyme histochemical methods. In the experiments, 250 fertile eggs of Ross-308 broiler strain were divided into two groups, the control eggs were maintained under optimal conditions (37.8°C and 65% ± 2% relative humidity, rh) during the whole incubation period. Heat-stress imposed eggs were maintained under normal conditions (37.8°C and 65% ± 2% rh) until the 10th day of incubation, and then, continuously (24 h per day) exposed to high temperature (38.8°C and 65% ± 2% rh). Tissue samples were taken from 10 animals of each group at the 11th, 13th, 15th, 18th, 21st days of incubation. Tissue samples were processed by enzyme histochemical methods in addition to routine histological techniques. The relative tibia weights and tibia length were lower in the heat-stress group compared to the control group. The results of the measurements of the growth plate showed that the proliferative zone was narrowed whereas, the transitional and hypertrophic zone were thickened in the heat stress group. Alkaline phosphatase (ALP) density was significantly decreased in the heat-stress group compared to the control group. In conclusion, bone formation and growth plate formation are crucial for embryo development and 1°C higher from optimum may increase the incidence of skeletal disorders and leg problems in broiler chickens which is one of the major animal welfare concerns for the poultry industry.