Effect of vitamin premix withdrawal in diets containing different levels of energy on performance and carcass characteristics of broilers subjected to heat stress

This experiment was conducted to evaluate the effect of vitamin premix withdrawal from diets containing different energy levels on growth performance and carcass characteristics of broilers subjected to heat stress in a completely randomized design with 2×3 factorial arrangement containing, 2 levels of energy (Low and High energy) and 3 levels of vitamin premix withdrawal (28, 35 and 42 days). Three hundred and thirty six Ross 308 broilers (male sex) were allocated to 6 experimental treatments with 4 replicates of 14 chicks each. The results showed that broilers were fed high energy diet had significantly higher body weight gain than those were fed low energy diet (P<0.05). The vitamin premix withdrawal and energy level had no significant effect on feed intake. Broilers that their vitamin premix were withdraw at 28 days rather than other groups (35 and 42 days) had relatively lower body weight gain and significantly higher feed conversion ratio (P<0.05). Carcass percentage and abdominal fat were significantly higher in broilers fed higher energy diet than those were fed low energy diet (P<0.05). Carcass characteristics were not affected by the time of vitamin premix withdrawal. Based on the results of this experiment, increasing of dietary energy level resulted to improve broiler's performance subjected to heat stress, although the abdominal fat increases. Also, it is possible to withdraw vitamin premix one week before slaughtering (35 days), but it's withdraw two weeks before slaughtering (28 days) may decrease the performance of broilers.