Influence of Protein and Energy and Growth and Protein Utilization in the Growing Chicken

Abstract

A factorially arranged experiment involving 4 levels of metabolizable energy (2.50, 2.78, 3.05 and 3.33 kcal/g), and 5 levels of protein (10, 14, 18, 22 and 26%) was conducted with chickens to study the effects of energy and protein on growth and protein utilization. To achieve the same balance of amino acids at all levels of protein a single protein source was used. Increasing the protein level to 26% gave an increase in weight gain and feed efficiency even with the lowest energy diet. Net protein utilization (NPU) values increased slightly at the 2 lowest protein levels as the energy level of the diet was increased. There was a much greater increase in NPU values with increasing levels of energy at the higher than at the lower levels of protein. The results indicate that both protein and energy levels should be taken into consideration when evaluating protein supplements. It is suggested that higher than maintenance levels of protein, along with a calorie-to-protein ratio in the range 55 to 65 be used for the determination of NPU values for application to the growing chicken. Nitrogen retention values followed the same trend as the NPU data except at the low protein levels where the lack of a correction for nitrogen for maintenance resulted in misleading retention values at the low levels of protein.