Low protein diets have improved nutrient utilization while maintaining animal performance. However, these diets may be limiting in nitrogen (N) content to meet non-essential amino acid (NEAA) requirements, potentially altering essential amino acid (EAA) utilization and requirements. Inclusion of a source of non-protein nitrogen (NPN) may be beneficial for improving EAA utilization for lean gain. An N-balance study was conducted to determine the lysine requirement for maximum nitrogen retention (NR) when pigs are fed diets without and with the inclusion of NPN in the form of ammonium phosphate (AP). Lysine and N content had an effect (P < 0.05) on fecal and urinary N output, digestibility, and plasma urea nitrogen (PUN), including an increase in NR and decrease in urinary N output with inclusion of NPN and increasing Lys (P < 0.01). A decrease in PUN was observed with increasing Lys (P < 0.05). The linear breakpoint model indicated NR was maximized at 1.00% SID Lys (15.6 g/d NR; R2 = 0.68) in pigs fed no AP and at 1.09% SID Lys (16.4 g/d NR; R2 = 0.61) in AP-fed pigs. These results indicate that diets deficient in dietary N reduce NR and Lys requirement, which were in turn increased with NPN supplementation. Future research should continue to assess the impact NPN inclusion has on low-protein diets that are limiting in NEAA-N.
Inclusion of non-protein nitrogen in grower pig diets on lysine requirement for maximum nitrogen retention (full article)
