PSII-11 Supplementation of Non-Protein Nitrogen to a Nitrogen-Deficient Diet Increases Lysine Requirement for Nitrogen-Retention

Abstract

Abstract Low protein (LP) diets have improved nutrient utilization while maintaining animal performance. Regardless, 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 non-protein nitrogen (NPN) may be beneficial for improving utilization of EAA in LP diets. The objective of this study was to determine the impact of NPN in an N-deficient diet, as indicated by EAA-N:total N ratio (EAA-N:TN) on the Lys requirement for nitrogen retention (NR). A total of 90 growing barrows (initial BW of 20.4 ± 0.46 kg) were randomly assigned to 1 of 10 dietary treatments (n = 9 pigs/treatment) in 9 blocks in a 2 × 5 factorial design. Diets contained no ammonium phosphate (NAP; EAA-N:TN of 0.56) or were supplemented with 1.7% ammonium phosphate (AP; EAA-N:TN of 0.50) with graded levels of dietary lysine [Lys; 0.8%, 0.9%, 1.0%, 1.1% and 1.2% standardized ileal digestible (SID)]. Diets were corn and soybean meal-based and formulated to meet or exceed nutrient requirements according to NRC (2012). Diets were fed at 2.8 × maintenance metabolizable energy requirements in two equal meals per day. A 4-d nitrogen balance collection period was conducted following a 7-d dietary adaptation period. Urine was collected quantitatively, and fresh fecal samples were obtained daily. Nitrogen retention was determined as the difference between N intake and output (fecal and urinary). Linear breakpoint modeling with PROC NLIN was used to estimate Lys requirement. Nitrogen retention was optimized at 1.00% SID Lys (15.6 g/d NR; R2 = 0.68) in pigs fed NAP diets and 1.09% SID Lys (16.4 g/d NR; R2 = 0.61) in pigs fed AP diets. Overall, deficient dietary N reduced NR and Lys requirement, which were increased with NPN supplementation.