468 - Effect of Low-Protein Diets Having Constant...

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Effect of Low-Protein Diets Having Constant Energy-to-Protein Ratio on Performance and Carcass Characteristics of Broiler Chickens from One to Thirty-Five Days of Age Z. Kamran,* M. Sarwar,* 1 M. Nisa,* M. A. Nadeem,† S. Mahmood,‡ M. E. Babar,§ and S. Ahmed‡ *Institute of Animal Nutrition and Feed Technology, University of Agriculture, Faisalabad, Pakistan 38040; †Animal Nutrition, Animal Science Institute, National Agriculture Research Centre, Park Road, Islamabad, Pakistan 45500; ‡Department of Poultry Science, University of Agriculture, Faisalabad, Pakistan; §Department of Livestock Production, University of Veterinary and Animal Sciences, Lahore, Pakistan 54000 ABSTRACT A trial was conducted to determine the effect of low-protein diets with constant ME:CP ratio on performance and carcass characteristics of broilers from 1 to 35 d of age. Four experimental diets were formulated to have 4 levels of CP and ME, respectively, in each phase: 23, 22, 21, and 20% CP with 3,036, 2,904, 2,772, and 2,640 kcal/kg in the starter phase (1 to 10 d); 22, 21, 20, and 19% CP with 3,146, 3,003, 2,860, and 2,717 kcal/kg in the grower phase (11 to 26 d); and 20, 19, 18, and 17% CP with 3,100, 2,945, 2,790, and 2,635 kcal/kg in the finisher phase (27 to 35 d). Digestible Lys was maintained at 1.10, 1.02, and 0.90% of the diet in the starter, grower, and finisher periods, respectively. A total of 1,760 one-day- old Hubbard broiler chickens were randomly divided into 16 experimental pens, 110 chickens in each pen, and Key words : low-protein diet, energy:protein ratio, broiler performance, carcass characteristic, abdominal fat 2008 Poultry Science 87:468–474 doi:10.3382/ps.2007-00180 INTRODUCTION Lowering the CP content of broiler diets may reduce feed cost and allow for use of alternate feedstuffs. Some researchers have found that reducing dietary CP does not affect growth performance (Parr and Summers, 1991; Moran and Stilborn, 1996). However, rate and efficiency of growth is lower, and carcass composition becomes inferior in broilers fed diets in which CP has been lowered by more than 3%, even when all known nutrient require- ments are met (Fancher and Jensen, 1989; Aletor et al., 2000; Bregendahl et al., 2002; Sterling et al., 2005; Wal- droup et al., 2005). It is known that the CP and amino acid ( AA ) status of a diet influences the carcass composition of broilers, and decrease in dietary CP causes a decrease in carcass protein and an increase in carcass fat content (Si © 2008 Poultry Science Association Inc. Received May 3, 2007. Accepted October 28, 2007. 1 Corresponding author: [email protected] 468 each diet was offered to 4 replicates at random. Weight gain was linearly decreased ( P < 0.001), whereas feed intake and feed conversion ratio were increased ( P < 0.001) linearly as dietary protein and energy decreased during grower, finisher, and overall experimental peri- ods. Protein efficiency ratio and energy efficiency ratio were decreased ( P < 0.05) with low-CP and low-ME diets during the grower, finisher, and overall experimental pe- riod. However, carcass yield, breast meat yield, thigh yield, abdominal fat, and relative liver and heart weights were not affected by the treatments. Feeding broiler chick-
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