The impact of dietary nitrogen content and source on essential amino acid utilization and growth performance in growing pigs

Low protein diets have improved nitrogen (N) utilization, but dietary N for the endogenous synthesis of non-essential amino acids (NEAA) may be limiting. Inclusion of a non-protein nitrogen (NPN) may improve utilization of essential amino acids (EAA). A N-balance study was conducted, where 90 growing barrows were assigned to 1 of 10 dietary treatments. 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 Lys [0.8%, 0.9%, 1.0%, 1.1% and 1.2% standardized ileal digestible (SID)]. Nitrogen retention (NR) 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, a diet deficient in N (EAA-N:TN of 0.56) reduced NR and Lys requirement, which were increased with NPN supplementation. A follow-up study was conducted, where 240 mixed-sex growing pigs were housed in groups of 5 pigs/pen. Pens were assigned to 1 of 6 dietary treatments for 28 d. The same NAP and AP diets were used with graded Lys at 1.03%, 1.15% or 1.27% SID. Average daily gain and final body weight were maintained, feed intake reduced, and feed efficiency increased with AP inclusion. Greater lysine increased average daily gain and final body weight. Lean depth was increased in AP-fed pigs. Overall, including supplemental N, as NPN, can improve lean gain and feed efficiency while maintaining overall growth performance in growing pigs.

Keywords: non-protein nitrogen, lysine, swine.