Effect of calorie to protein ratio on the degree of fatness in broilers fed on practical diets 1

Three trials were carried out with broilers to compare the effect of different calorie to protein (C : P) ratios in practical‐type diets with the amount of carcass fat at 8 or 9 weeks of age. The latter was estimated on the basis of the concentration of fat or dry matter in a sample of back skin and by visually scoring the amount of abdominal fat.

Rearing broilers on diets containing protein levels slightly above or below the accepted optimum did not affect growth rate. However, in most comparisons the high‐protein diets brought about better food to gain ratios, and in all comparisons they produced relatively lean carcasses. Increasing or decreasing the protein level of finisher diets resulted in a decrease or increase, respectively, in the degree of fatness. A 2‐week period was sufficient to create or reverse these trends in a pronounced manner.

Dietary oil supplementation per se did not increase the amount of carcass fat as long as the C : P ratio was kept constant. If there existed any consistent trend at all, it appeared to act in the opposite direction, towards a decrease in carcass fat.