Effects of Dietary Protein Level on Carcass Composition of Broilers at 5 to 15 Days of Age.

Abstract

Few reports have been available concerning the relationship between dietary protein level and body composition of broilers at starting stage (0-3 weeks of age) under the same metabolizable energy (ME) condition. Preceding determination of the amino acid requirement of broilers using body weight gain as a main criterion, the effects of dietary crude protein (CP) on the carcass composition of broilers were studied.To the experimental diets mainly consisting of corn, whole egg protein was added as a good protein source to contain 3,200 kcal ME/kg and 6 levels of CP from 12.1 to 21.1% arithmetically. Five broilers for each diet were fed ad libitum the experimental diets from 5 to 15 days of age after nutritional effects of yolk sack decreased. On the 15th day, they were sacrificed after recording the body weight and feed consumption, and moisture, fat, protein and ash contents of the carcass were determined.The body weight gains reached the maximum level at 16.2% CP and the feed efficiency reached the maximum level at 15.0% CP.Percentage of the carcass moisture (Y1), protein (Y2) and ash (Y3) increased linearly and, to the contrary, that of fat (Y4) decreased linearly with increasing the dietary CP level as follows: Y1=0.284X+61.27(r2=0.658) Y2=0.236X+11.50(r2=0.606) Y3=0.266X-0.86(r2=0.939) Y4=-0.786X+28.09(r2=-0.935) where X is percentage of the dietary CP. The highest ratio of retained protein, to ingested one was 71.9% at 14.9% of the dietary CP level and that of retained energy to ingested one was 52.6% at 14.9% of the dietary CP level.The contents of the digestive tracts increased with increasing the dietary CP level and body size. However, they did not affect the estimation of the requirements.