When dietary protein is reduced by more than 3%, non-essential amino acids or total dietary protein may become limiting for maximum nitrogen (N) retention (i.e., lean gain) and growth performance. It has been suggested that the ratio of essential amino acid-nitrogen to total nitrogen (E:T) can be used as an indicator of N sufficiency in the diets. The objectives of this study were: to determine the effect of E:T ratio on the lysine requirement for N retention in growing pigs; determine the effect of E:T ratio and inclusion of non-protein N (i.e., ammonium phosphate) on the lysine requirement for N retention in growing pigs; and determine the effect of E:T ratio, lysine content, and non-protein N inclusion on growth performance, nitrogen output, and body composition of growing pigs.
Results indicate that non-essential amino acids, or total dietary nitrogen, become limiting in diets with a high E:T ratio. This deficiency can be mitigated through supplementation with either intact protein or a source of non-protein N (i.e., ammonium phosphate). An increase in dietary lysine is required when diets contain sufficient nitrogen as a result of improved N retention (i.e., lean gain). Including a source of non-protein N improved feed efficiency while maintaining growth performance, indicating that ammonium phosphate is an appropriate source of N in swine diets. Nutritionists should consider the E:T ratio in diet formulation as an indication of N sufficiency.
Dietary nitrogen content affects lysine requirement and nitrogen utilization and retention in growing pigs (full article)
