81 Indian Journal of Animal Sciences 81 (11): 1165–1172, November 2011 Effect of low crude protein diets with constant metabolizable energy on performance of broiler chickens from one to thirty-five days of age ZAHID KAMRAN 1 , MAHR-UN-NISA 2 , MUKHTAR AHMAD NADEEM 3 , MUHAMMAD SARWAR 4 , SYED SHAKIL AMJID 5 , RIAZ HUSSAIN PASHA 6 and MUHAMMAD SHAHID NAZIR 7 University of Agriculture, Faisalabad 380 40 Pakistan Received: 17 March 2011; Accepted: 5 June 2011 ABSTRACT A trial was conducted to study the effect of lowering dietary crude protein (CP) on the performance of broilers from 1 to 35 d of age. Four experimental broiler diets were formulated. Diet A served as control with 23, 22 and 20% CP in starter, grower and finisher periods, respectively while in diets B, C and D, the CP was reduced to 22, 21 and 20% in starter; 21, 20 and 19% in grower and 19, 18 and 17% in finisher period, respectively. All diets were isocaloric within a phase (2,925, 3,075 and 3,125 kcal/kg ME for starter, grower and finisher periods, respectively). Weight gain, feed intake, feed conversion ratio (FCR), total ME intake and energy efficiency ratio were similar across treatments. However, total protein intake decreased and protein efficiency ratio increased with low CP diets during all growth periods. The carcass characteristics were similar among treatments. In conclusion, the dietary CP level could be reduced without harmful effects on the performance of broilers when supplemented with limiting AA. Key words: Amino acids supplementation, Broilers, Carcass characteristics, Growth performance, Low CP diets Protein is generally considered one of the major cost components of the poultry diets (Kamran et al. 2004). In recent years, the use of low CP diets with AA supplementation in broilers increased due to the reasons of feed cost, feed efficiency and flexibility in feed formulation (Kidd and Kerr 1996, Kamran et al. 2008). However, the balance of AA is important while reducing CP to ensure optimum performance (Ojano-Dirain and Waldroup 2002). Although, there is a biological limit to which dietary CP content can be reduced, some attempts have been made to reduce dietary CP level with no adverse effect on broiler performance (Moran and Stilborn 1996, Ayasan et al. 2009, Maksoud et al. 2010, Widyaratne and Drew 2011). However, some researchers have found that growth rate, feed efficiency and carcass composition is affected in broilers fed low CP diets although the levels of essential AA and other nutrients were kept to meet requirements (Aletor et al. 2000, Bregendahl et al. 2002 and Waldroup et al. 2005). In Pakistan, usually low nutrient density diets are formulated for open type farming. The environmentally controlled farming has increased rapidly with rearing of Hubbard strain during the past few years. However, very little work has been done on low CP diets in environmentally controlled farming using nutrient recommendations for Hubbard strain. Due to already present discrepancies and a limited number of studies under these conditions, the present study was planned to examine the effect of low CP diets adequate in limiting AA on broilers performance and carcass characteristics from 1 to 35 d of age. MATERIALS AND METHODS The experiment was conducted in an environmentally controlled house. Hubbard broiler strain was used in the experiment and nutrient recommendations for Hubbard strain were used as control (Hubbard 2004). The whole experimental period was divided into 3 phases: starter (1 to 10 d), grower (11 to 26 d) and finisher (27 to 35 d) according to Hubbard (2004). Present address: 1,6 Assistant Professor (zkami79 @yahoo.com; riazpashauaf@hotmail.com), University College of Veterinary and Animal Sciences, The Islamia University of Bahawalpur. 2 Associate Professor, 4 Professor (linknisa@gmail.com; drms01@gmail.com), Institute of Animal Nutrition and Feed Technology, Faisalabad. 3 Principal Scientific Officer (drmukhtarnadeem@ yahoo.com) Animal Nutrition, Animal Science Institute, National Agriculture Research Centre, Park Road, Islamabad; 5 Market Development Officer (shakeelamjid@gmail.com), Pioneer Pakistan Seed Limited, Pakistan. 7 Research and Development Officer (msnshahid@yahoo.com), Jadeed Feeds Khanewal, Pakistan.