Net Energy to Improve Pullet Growth with Low Protein Amino Acid-Fortified Diets

Abstract

Three experiments were conducted to investigate the poor growth rate usually seen with growing Leghorn pullets on low protein amino acid-fortified diets. It was hypothesized that such poor growth may in part be caused by increased net energy of diets as soybean meal is replaced by amino acids. With higher effective energy (even at constant ME) feed intake will decline and amino acid supply will diminish. In two experiments diets were formulated to 2950 kcal ME/kg or 2360 kcal NE/kg with 18, 15, or 13% CP and using synthetic amino acids to meet requirements. Pullets fed the lower protein diets were consistently smaller regardless of energy evaluation system. In a third study 13% CP diets were formulated to 2950 kcal ME/kg and synthetic amino acids added to either meet requirements or to equate all total levels provided by an 18% CP diet. Adding all such amino acids corrected the growth depression (P<.05), although pullets were still slightly smaller than control-fed birds. In these experiments, the NE system of energy evaluation did not resolve problems seen in formulating diets low in crude protein. Results indicate that at this time it is uneconomical to consider synthetic amino acids other than methionine, lysine, tryptophan, and threonine.