Relationship between dietary amino acid release kinetics and nitrogen deposition in growing pigs

Although the protein content of swine diets is formulated based on the ileal digestibility of protein and amino acids (AA) under current nutrition requirements, the nitrogen utilization efficiency of swine varies based on protein source, which may be related to AA release kinetics. In this experiment, a 2 × 2 factorial arrangement with casein (CAS)-enriched or corn gluten meal (CGM)-enriched protein sources at different digestible crude protein levels (normal [N], 13%; and low [L], 11%) were applied to 24 crossbred (Duroc × Landrace × Yorkshire) growing pigs (average body weight = 43.3 ± 3.5 kg) in 4 treatments (N.CAS, L.CAS, N.CGM, L.CGM, respectively) to investigate the effects of AA release kinetics on nitrogen deposition in growing pigs. Standardized ileal digestible AA in all diets were balanced by adding individual AA to meet the nutrient requirements. The AA release kinetics were detected in vitro by measuring the hydrolysis of various protein diets under pepsin and trypsin conditions. The results demonstrated that the time of AA release peak in the CGM diet was 12 h later than that in the CAS diet. The synchronization indices of dietary AA release in N.CAS, N.CGM, L.CAS, and L.CGM were 23.73%, 29.37%, 23.40%, and 26.07%, respectively. The N.CGM had the poorest AA release synchronism while the N.CAS had the greatest among the 4 diets. However, within the pigs, L.CAS and N.CGM showed the highest (81.08%) and lowest (73.54%) nitrogen biological values, respectively, despite the standard ileal digestible AA levels being equal for all diets. These results indicate that the release kinetics of dietary AA had great effect on nitrogen deposition. To optimize nitrogen deposition, AA release kinetics and composition should be taken into consideration when formulating diets for growing pigs.