Non-protein nitrogen improves feed efficiency of growing pigs fed a diet deficient in non-essential amino acid nitrogen
In pig diets the balance between essential amino acids (EAA) and total nitrogen (N) should be considered, especially when large amounts of crystalline EAA are supplemented and N levels are reduced. When lowering dietary N, the dietary supply of non-essential amino acids (NEAA) is reduced and the need of N for endogenous synthesis of some NEAA may be increased, requiring N from either catabolism of excess EAA and NEAA or non-protein nitrogen (NPN). The objective of the present study was to determine the effect of supplementing NPN, in the form of ammonium salts, in diets deficient in NEAA-N on performance of growing pigs. In total, 48 gilts (initial BW of 15.2 ±1.3 kg) were randomly assigned to 4 diets: (1) positive control (PC; 13.39% CP), not deficient in EAA and NEAA-N, and all N was supplied from intact protein (casein and soybean meal) or crystalline EAA, (2) negative control (NC; 10.19% CP), supplying the same amount of potentially limiting EAA as PC, but deficient in NEAA-N, (3) NC with 3 g/kg added ammonium (Low NPN), and (4) NC with 6 g/kg added ammonium (High NPN); the latter containing the same amount of digestible N as PC. Pigs were grouped in 2 pigs per pen with 6 pens per treatment. BW gain and feed intake were monitored weekly during 3 weeks, and blood samples were taken on days 14 and 21 to determine plasma urea concentration. Week 1 yielded poor growth performance and was considered a week of adaptation. During weeks 2 and 3, BW gain was not affected by NPN (P > 0.10); while feed intake tended to decrease with increasing dietary NPN (P = 0.06). Gain:feed, improved linearly with supplementation of NPN in diets (P < 0.05; 0.45, 0.47 and 0.51 for NC, Low and high NPN during weeks 2-3). Gain:feed for High NPN was similar to that for PC (P > 0.10: 0.51 and 0.52 for High NPN and PC; week 2-3). Plasma urea concentration was low and not different between diets (P > 0.10). Dietary supplementation with NPN, in the form of ammonium salts, can improve pig performance when pigs are fed diets deficient in NEAA-N.
Keywords: growth, nitrogen, pigs.