Abstract
Optimizing low-protein (LP) diets in swine nutrition is critical for reducing nitrogen excretion and resource waste while reducing meat quality. However, LP diets may disrupt amino acid (AA) balance, affecting growth and health. Supplementing with nonprotein nitrogen sources such as diammonium phosphate (DP) can enhance nitrogen utilization and support protein synthesis efficiently. This study aimed to investigate the effects of adding DP to LP diets on growth performance, organ indices, carcass traits, meat quality, and AA composition in growing pigs. Seventy-five barrows (Duroc × Landrace × Yorkshire) were randomly assigned to 5 dietary treatments: Pos Ctrl (CP: 13.50%), DP1 (CP: 12.00% + DP), DP2 (CP: 10.50% + DP), DP3 (CP: 9.00% + DP), and Neg Ctrl (CP: 9.00%). Each DP-supplemented diet aimed to maintain an essential AA nitrogen to total nitrogen (EAA-N/TN) ratio of 0.48. The pigs had free access to food and water for the 41-day experimental period, with body weight and feed intake were recorded monthly. After overnight fasting, pigs were euthanized, and carcass traits, meat quality, and organ indices were assessed. Blood, liver, and muscle samples were collected for analyses of plasma biochemistry and AA profiles. The study found that feeding the DP2 diet resulted in the best growth performance, while the DP3 diet significantly improved ADG and G:F compared with the Neg Ctrl diet. The DP3 diet also significantly increases relative liver weight compared with the Neg Ctrl diet. Although no significant differences were observed in carcass traits or meat quality among the dietary treatments, the DP3 diet had a tendency to reduced plasma total protein levels relative to the Neg Ctrl diet. Feeding the DP3 diet did not alter the free AA profile in plasma and liver of growing pigs compared with the Neg Ctrl diet, and there was no effect between the different diets on the hydrolyzed AA profile in muscle. Furthermore, the DP3 diet significantly increased Tau concentrations in the longissimus dorsi muscle (LM) while significantly reducing Car levels compared with the Neg Ctrl diet. In conclusion, these results suggest that adding DP to the LP diet can enhance growth performance and improve meat flavor-related AA content without compromising carcass traits or meat quality.