Breed Difference in the Pattern of Growth Response to the Change in the Dietary Energy and Protein Levels

Abstract

In 18 experiments, 2, 679 one-day-old chicks of 5 pure- and 7 cross-breds were fed one of 9 experimental diets containing one of 9 combinations of 3 dietary energy levels, i.e. 4.2, 3.6 and 3.0kcal metabolizable energy/g diet, and of 3 dietary protein levels, i.e. 26, 21 and 16%. Body weight gain and feed intake for 4 weeks were recorded, and the breed difference in the change in the responses, i.e, body weight gain and feed efficiency, corresponding to the change in dietary energy and protein levels was compared.The following conclusions were obtained.1. Response of chicks of all the breeds tested could be well described by the quadratic equation as the function of dietary energy and protein levels. Convex elliptic paraboloid could be fitted to the response surfaces of the chicks.2. Breed difference was observed in the response pattern of body weight gain among the 5 pure-breds tested, which could be grouped into 4 based on the response pattern. White Leghorns (WL) and New Hampshires (NH) showed similar response pattern and could not be distinguished from each other. White Plymouth Rocks (WR) and White Cornishes (WC) had sharper responses to the change in dietary energy and protein levels, respectively, than those of WL and NH. Barred Plymouth Rocks (BR) characteristically showed dull responses to the change in both dietary energy and protein levels.3. Breed difference was not observed in the response patern of feed efficiency, i.e. body weight gain per unit of feed intake.4. Difference in the response pattern of body weignt gain was closely related to the breed difference in the ability to take diet of various composition. Feed intake of BR dropped linearly with the increase in dietary energy level, while that of WR was almost constant, regardless of the composition of diet.5. Although the difference in body weight was observed between both sexes, sexual difference was not observed on the response patterns of body weight gain.6. Breed difference in the responses themselves, i.e. body weight gain and feed efficiency, of the chicks fed the diet of the same composition wes not observed in these trials, mainly due to the large variance of error between the replications.