COMPARATIVE-EVALUATION OF 3 COMMERCIAL BROILER STOCKS IN HOT VERSUS TEMPERATE CLIMATES

Hot climate is a major Limiting factor of broiler production in tropic al and subtropical regions. The use of standard stocks in hot climates may result in large economic losses because genotypes selected in tem perate climates may respond differently to the high ambient temperatur es in hot regions or seasons. The summer and fall in Izmir, Turkey, pr ovided the natural hot and temperate climates, respectively, for this study. Broiler chicks were obtained from three commercial stocks, all bred in temperate climates. Male and female chicks, 60 per pen, were h oused in four pens per stock per season. Individual BW was determined at hatch, and at 4 and 7 wk of age. Feed consumption and efficiency we re determined per pen. Feathering was scored at 4, 5, and 6 wk of age. Body temperature was measured twice on three birds per sex per pen, 1 6 h and immediately before slaughter, and feather weight was determine d for each of these birds.The two seasons clearly differed in ambient temperature at the broiler house, and consequently, BW at 7 wk was sig nificantly lower in the summer than in the fall in all stocks, with an average reduction of 23%. The season effect was largest (33.5%) on BW gain from 4 to 7 wk, along with 23 and 15% reductions in feed consump tion and efficiency, respectively, during these 3 wk. A significant se ason by stock interaction was detected for BW gain from 0 to 4 wk and 4 to 7 wk. The three stocks exhibited similar 4- to 7-wk BW gains unde r the temperate fall climatic conditions, but differed significantly i n the summer. These differences were not related to normal differences in feather coverage or body temperature, suggesting that standard bro iler stocks must be tested in hot climates in order to find the one mo st suited to these conditions.