Body Composition, Protein Deposition, and Efficiency of Lysine Utilization of Growing Pigs Fed Crystalline or Protein-Bound Lysine

2004 University of Nebraska Extension Swine Report. Two 4-week experiments were conducted to determine body composition and lysine utilization for protein deposition (PD) in barrows and gilts. Thirty-two growing pigs (16 barrows and 16 gilts; average initial body weight of 40.4 lb) were used in each experiment. Pigs were randomly allotted to one of seven dietary treatments. Four pigs (two barrows and two gilts) were killed at the start and the remaining pigs were killed at the end of the experiments to determine body composition. There were two replications per treatment in each experiment for a total of four replications. Dietary treatments consisted of a basal diet (0.55% lysine) and diets containing 0.65, 0.75, and 0.85% lysine that were achieved by adding lysine to the basal diet from either soybean meal (SBM) or L-lysineHCl (crystalline). Body protein concentration was greater (P < 0.01) in pigs fed the 0.75% crystalline- supplemented diet than in pigs fed SBM at the same concentration. Gilts had greater (P = 0.05) body lysine concentration than barrows. Body PD and lysine deposition increased linearly with dietary lysine concentration (P < 0.01), but were not different between the two sources of lysine (SBM vs crystalline, respectively) at the same concentration. Barrows and gilts had similar PD and lysine deposition. Body fat concentration decreased (P < 0.01) as the dietary lysine concentration increased for both lysine sources; however, fat deposition was not affected by diet. Water deposition increased with dietary lysine concentration (P = 0.05). Body ash content was similar in pigs fed crystalline or SBM-lysine. The results suggest that PD of growing pigs fed lysine from SBM is similar to that of pigs fed crystalline lysine. Pigs fed 0.75% or 0.85% total lysine (0.20% or 0.30% from SBM) had greater (P < 0.05) efficiency of lysine utilization than pigs fed crystallinesupplemented diets at the same concentration. Gilts utilized lysine from SBM more efficiently than barrows (P < 0.05) at the dietary lysine concentration of 0.75 and 0.85%. The results indicate no significant differences in PD of pigs fed supplemented diets from L-lysineHCl and soybean meal. However, it appears that the efficiency of lysine utilization of gilts fed diets supplemented with SBM-bound lysine is greater than that of barrows. Supplementing low-protein diets with crystalline amino acids at adequate concentrations can offer environmental benefits towards reducing nitrogen excretion without affecting protein deposition.