Effect of feed restriction and different energy and protein levels of the diet on growth performance and growth hormone in broiler chickens

Abstract

The aim of this study was to investigate the effects of feed restriction and different energy and protein contents of the diet on performance and growth hormone concentration in broiler chicken. Five hundred and seventy six day old Ross male broiler chicks were used in a 2×2×3 factorial arrangements in a completely randomized design experiment. Feeding programs consisted of ad libitum and Skip-a-Day (SAD) feed restriction, two energy levels (3100 and 2800 kcal ME kg-1) and three protein levels (22.3, 19.3 and 16.3% CP). Feed restriction (SAD) was applied during 22-32 d of age. Corn-soybean meal based diets containing vegetable oil were used. Body weight and feed intake were recorded weekly. At 21, 32 and 49 day of age, one bird from four replicate of each treatment was selected randomly to collect blood sample and then carcass, breast and thigh weight were measured. Blood samples assayed for Growth Hormone (GH) concentration by RIA. Feed restriction decreased feed intake and body weight gain (p<0.001 ) of birds during 22-32 and feed intake during 32-49 day of age, while body weight gain was not affected during this period. Also, feed restriction decreased Feed Conversion Ratio (FCR) (p<0.01 ) and body weight gain (p<0.001 ) during 22-32 day of age. Feed intake (p<0.001 ) and body weight gain increased in broilers fed on low-energy diets compared with those fed on high-energy diets during different periods. Increasing levels of protein increased feed intake (p<0.001), body weight gain and improved FCR (p<0.001 ) as compared with least level of protein. Feed restriction decreased carcass percentage (p<0.001) and increased thigh percentage (p<0.01) at 32 day of age. Carcass percentage (P<0.05) and breast percentage increased in broilers fed on low-energy diets compared with those fed on high-energy diets during different periods. The low protein diet decreased carcass percentage (p<0.01), breast percentage (p<0.001 ) during different periods and thigh percentage (p<0.05) at 21 day of age. The result of this experiment indicated that the lowest protein level had the highest growth hormone concentration at 49 day of age. The low energy diet increased growth hormone concentration (p<0.05) at 21 day of age. © 2010 Asian Network for Scientific Information.