Z. Kamran, M. Aslam Mirza, Ahsan-ul-Haq¹ and S. Mahmood¹

Institute of Animal Nutrition and Feed Technology, ¹Department of Poultry Husbandry, University of Agriculture, Faisalabad, Pakistan

    A six-week trial was conducted to study the effect of decreasing dietary crude protein (CP) level on the performance of broilers in hot climatic conditions. Four experimental rations having CP 23 (control group), 22, 21 and 20%, with optimal amino acid balance were prepared. All the four rations were isocaloric having ME 3200 kcal/kg with Energy: Protein (E:P) 139.0, 146.5, 152.4 and 160 in diets A, B, C and D respectively. One hundred and twenty day-old chicks were randomly distributed into 12 experimental units, each having 10 chicks. Rations were randomly allotted to experimental units such that each unit received three replicates. The experimental diets were fed to birds from day 1^st to 42^nd. Performance of birds was monitored in terms of weight gain, feed consumption and feed conversion ratio (FCR). At the end of experiment, two birds per each replicate were randomly selected and slaughtered to record the data on carcass yield, breast meat yield, abdominal fat and composition of breast meat. Results of the trial suggested that weight gain was significantly (P<0.01) increased in birds on diets with CP 20 and 21%. Feed consumption and FCR remained un-changed for all the treatment groups. Eviscerated carcass yield was significantly (P<0.05) higher for the group fed on diet with 20% CP. Breast meat yield, abdominal fat and composition of breast meat also remained un-changed. Economic evaluation of the trial revealed that decreasing CP levels from 23 to 20% resulted in reduced feed cost per kg of live weight gain, which clearly indicated that this approach was useful especially in severe summer conditions. The overall picture of the study suggests that dietary protein level of broilers could be reduced from 23 to 20%, with beneficial effects on growth performance and carcass characteristics and increased economic returns in hot environmental conditions, provided that levels of essential amino acids are closely looked after.

Key words: Dietary protein, amino acids, broilers.