Abstract

An experiment was conducted to evaluate crude protein level on lysine requirements and performance of male broiler chickens. From 21 to 42 day old chicks were fed one combination of dietary lysine and CP (18, 20 and 22% crude protein and 0.08, 0.9, 1 and 1.1% lysine) in a diet containing 3.200 kcal/kg ME. Variables measured consisted of feed intake, body weight gain, feed conversion ratio, percentage of fat pad carcass, breast and thigh weight. The lysine requirement was estimated by broken line methodology based on body weight gain, feed conversion ratio, carcass and breast weight recorded in the grower period. There were significant effects of crude protein level on body weight gain, feed intake, feed conversion ratio and percentage of fat pad that existed. The body weight gain and feed intake increased and percentage of fat pad decreased as crude protein increased in the diet. However, increasing lysine in the diets significantly increased body weight gain, breast meat, thigh and carcass weight and decreased feed conversion ratio and percentage of fat. Body weight gain, feed conversion ratio, carcass weight and percentage of fat pad were significantly affected by lysine × crude protein interaction. Predicted lysine requirements for body weight gain, feed conversion ratio, carcass and breast meat weight with increasing crude protein level were increased as percentage of the diet. The quadratic-broken line model estimated higher requirements than the straight-broken line model for all response criteria. The highest (1.097±0.073) and the lowest (0.907±0.0046) lysine requirement with straight-broken line analysis were estimated for breast meat weight at 22% crude protein level and body weight gain at 18% crude protein, respectively. The results suggest that lysine requirement affected by dietary crude protein level, and for estimation lysine requirement must be defined best criterion response.

Key words: Lysine, crude protein, broiler, broken line.