EFFECTS OF UREA AS A SOURCE OF EXTRA DIETARY NITROGEN ON GROWTH-PERFORMANCE AND CARCASS TRAITS OF FINISHER PIGS

Forty-two crossbred pigs weighing 54.2 +/- 5.5 kg were used to evaluat e the value of urea as a source of extra nitrogen (N) to enhance carca ss leanness of finisher pigs. Three soybean meal (SBM) diets were form ulated to contain 0.60 and 13.2% (Low), 0.73 and 15.5% (Med) or 0.85 a nd 16.7% (High) lysine and crude protein (CP), respectively. Two urea diets were formulated to be iso-nitrogenous (Iso-N) to the Med and Hig h SBM diets. Two additional urea diets were formulated to be iso-lysin ic (Iso-Lys) to the Med and High SBM diets by incorporating crystallin e amino acids. The indispensable amino acid contents were at least 20. 8 and 41.7% above the current NRC requirements for the Med and High Is o-Lys diets, respectively. To ensure an adequate supply of CP from com mon feed ingredients for pigs, corn and SBM contributed 13.2% CP to fo ur urea diets, and urea supplied additional CP equivalent. Pigs were h oused individually, and allowed ad libitum access to feed. All pigs we re slaughtered at an average weight of 103.2 +/- 4.5 kg. Pigs fed the Low SBM diet tended to grow faster (P = 0.09) than those fed other die ts (1.09 vs 1.02 kg/day). However, the average backfat (BF; 36.4 vs 32 .1 mm; P < 0.05) and 10th rib BF (33.1 vs 28.9 mm; P = 0.10) were high er, and carcass specific gravity (1.046 vs 1.041; P < 0.05) and propor tion of lean (47.6 vs 44.7%; P = 0.08) were lower in pigs fed the Low diet than those fed the Med and High diets, indicating that a higher w eight gain was achieved by the increased rate of fat accretion. The re sults indicated that the carcass quality was improved by increasing ly sine and(or) N levels from low to medium regardless of the source [SBM or urea and(or) amino acids]. In addition, simply incorporating urea to increase dietary N (Iso-N) from low to medium and amino acid supple mentation of urea diets (Iso-Lys) were equally effective in enhancing the carcass quality of pigs, indicating that overall utilization of di ets was improved by the inclusion of urea. There was, however, no impr ovement in the carcass quality of finisher pigs with further increases in dietary lysine and(or) N levels from medium to high.