Varying levels of
dietary protein (16, 20, 24, 28, 32, 36%) and energy (2600, 2800, 3000, 3200, 3400, 3600 kcal [metabolizable energy] ME/kg) were fed in a factorial arrangement to broilers to determine the effect of alteration in nutrient density on performance and economic traits.
Body weight and feed efficiency improved with increased
dietary protein or energy. However, a significant interaction between
protein and energy indicated the importance of a balanced energy:
protein ratio to achieve optimum performance. Sex differences in
protein requirements were observed for 49-day
body weights. Returns over feed costs remained essentially constant, providing a balance between
dietary protein and energy was maintained. However, an increase above 28% crude
protein or 3400 kcal ME/kg resulted in reduced returns as did excessive quantities of one nutrient relative to the other. Male broilers were able to accommodate a higher level of
dietary protein (24%) than female broilers (20%) before returns were reduced. Regression equations were derived for prediction of performance and economic parameters. Reliable estimates were obtained with the inclusion of
protein or energy intake in addition to diet composition.