Performance and Heat Tolerance of Broilers as Affected by Genotype and High Ambient Temperature

This experiment was conducted to evaluate the effects of the broiler’s genotype (Gt) and ambient temperature (Ta) on performance and core body temperature (Tcore) of broiler chicks. A factorial arrangement of two Gt (Hubbard and ISA J57 chicks) and two Ta (moderate, 23±0.5°C and hot, 33±0.5°C) were used in this study. Performance data (body weight gain, feed intake and feed:gain ratio) were determined weekly for six weeks. Chicks’ Tcore was measured using a biotelemetric system between Weeks five and six. Results showed that body weight gain and feed intake were significantly high, and feed:gain ratio was significantly low for Hubbard chicks compared to those of ISA J57 chicks. High Ta significantly reduced weight gain and feed intake. Furthermore, the reduction in body weight gain and feed intake under the hot Ta was more pronounced for Hubbard chicks than those of the ISA J57 chicks resulting in significant Gt by Ta interaction. Chicks grown under moderate Ta had significantly lower Tcore than those grown under hot Ta. The Tcore of the Hubbard chicks was significantly lower than that of the ISA J57 at the moderate Ta while under the hot Ta, the magnitude of the change in Tcore was more pronounced in Hubbard chicks than that of ISA J57; this resulted in a significant Gt by Ta interaction. The results of this study indicate that chicks with higher potential for growth under thermo-neutral temperature are more susceptible to heat stress than chicks with lower potential for growth. This maybe due, at least in part, to their lower body Tcore under moderate temperature and to the lesser ability of these fast growing chicks to regulate their Tcore when exposed to heat stress, as was clearly shown on these birds’ performance. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 10 : 1502-1506)