Combination of non-protein nitrogen and N‑carbamylglutamate supplementation improves growth performance, nutrient digestibility and carcass characteristics in finishing pigs fed low protein diets

This study was conducted to determine whether supplemental non-protein nitrogen (NPN) and/or N-carbamylglutamate (NCG) in the low protein diet enhance the growth performance, nutrient digestibility and carcass characteristics of finishing pigs. A total of 150 (Duroc boar× (Landrace boar × Yorkshire) sow) finishing pigs (initially body weight 74.3 ± 3.8 kg) were blocked by weight and sex, and allotted to one 5 treatments with 6 replicate pens (3 barrows and 2 gilts per pen). Diets were normal protein diet (NP, crude protein (CP) 136.4 g/kg), low protein diet (LP, CP 111.4 g/kg), LP supplemented with 0.8 g/kg NCG (LNCG, CP 111.8 g/kg), LP supplemented with 7.1 g/kg NPN (LNPN, CP 119.8 g/kg), and LP supplemented with 7.1 g/kg NPN and 0.8 g/kg NCG (LNN, CP 120.3 g/kg) and fed to pigs for 40 days. At the end of the experiment, 30 pigs (one barrow per pen) were slaughtered to evaluate carcass traits and meat quality. Compared to the LP group, the combination of NPN and NCG supplementation significantly increased (P < 0.05) the average daily gain (ADG) of finishing pigs. The coefficient of apparent total tract digestibility (CATTD) of gross energy (GE), crude protein (CP) and acid detergent fiber (ADF) in LP group were lower (P < 0.05) than that in the NP group, while LNN group significantly increased (P < 0.05) the CATTD of GE, CP, ether extraction (EE), neutral detergent fiber (aNDF) and ADF when compared with LP group. Similarly, the concentrations of arginine, isoleucine, threonine, glycine, serine, tyrosine, and citrulline in the serum of pigs fed LNN diet were higher (P < 0.05) than that in those pigs fed LP diet. The carcass traits and meat quality did not differ between the NP group and the LP group, but the combination of NPN and NCG supplementation in LP diet significantly increased (P < 0.05) the concentrations of intramuscular fat. Compared to NP group, LP group increased (P < 0.05) the concentration of C16:0 and decreased (P < 0.05) the concentrations of C20:4, C22:6 and polyunsaturated fatty acid (PUFA) in the M. longissimus lumborum of finishing pigs, and LNN group further decreased (P < 0.05) the concentrations of C18:2 and PUFA when compared with the LP group. This study indicates that dietary supplementation with both NPN and NCG has important complementary advantages in improving the growth performance and meat quality of finishing pigs fed low protein diet balanced with amino acids.