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Abstract
The effect of energy and protein dilution during 16 to 20 d of age, on performance, carcass characteristics and blood parameters of broiler chickens was studied in a completely randomized design with 3 treatments and 3 replicates in each treatment. A total of 144 mixed-sex chickens (Cobb 500) were randomly allocated to 9 pens. In order to dilute the diets three levels (0, 20 and 40%) of rice hull was used. During the experiment feed intake, body weight gain, feed conversion ratio were measured weekly. The results indicated that dilution of diet from 16 to 20 d of age increased feed intake in this period, but adjusted feed intake (excluded rice hull) was decreased (P<0.05). Restricted bird consumed more feed in the whole period of the experiment (16 to 44 d). With increasing dilution rate during restriction period, body weight gain of chickens decreased in comparison to control group (P<0.05). Due to compensatory growth after restriction period, restricted chickens had higher body weight gain than control groups at 44 d of age. Feed dilution up to 20 percent had not significant effect on feed conversion ratio in the whole period of the experiment. Diet dilution had not significant effect on carcass, breast meat, legs, proventriculus, heart and feet weight proportion. Diet dilution significantly increased gizzard weight proportion, and decreased abdominal fat pad weight, carcass crude fat, and increased carcass crude protein proportion (P<0.05). Feed dilution up to 20% increased HDL and decreased LDL concentration in plasma at 21 d of age. Diet dilution up to 40% decreased the concentrations of cholesterol, triglyceride, plasma T3, and increased the concentrations of uric acid and plasma T4 at 21 d of age (P<0.05). Diet dilution up to 20 percent increased plasma glucose concentration at 42 d of age (P<0.05). The results of the present study indicated that feed dilution with 20% rice hull during 16 to 20 d of age had not adverse effect on broiler performance and it also reduced abdominal fat pad weight and carcass crude fat proportion.