Effects of chronic heat exposure and protein intake on growth performance,nitrogen retention and muscle development in broiler chickens

The respective effects of ambient temperature, dietary crude protein and fe ed intake were investigated in finishing chickens and the consequence of pr otein supplementation under high temperature conditions was analysed in par ticular. Heat-related reduction in growth was associated with decreased nit rogen retention (-30 or -35 % according to the diet), which could not be ex plained by the observed lower feed intake alone. Tissue samples performed i n 5- to 6-week-old chicks showed varying effects of heat according to the m uscles studied: at 32 degrees C, the proportion of Pectoralis major muscle (in percentage of body weight) appeared slightly reduced (reduction lower t han 10 %), whereas the proportion of two leg muscles were increased (+10 to +15 % for the Sartorius muscle; +5 % for the gastrocnemius muscle). At 32 degrees C, providing a high protein diet significantly (P < 0.05) increased weight gain and feed efficiency, and slightly improved whole body protein deposition. (C) Inra/Elsevier, Paris.