Abstract: Dietary lysine concentration determines growth performance of pigs when all other nutrients fulfill the requirements. The optimal biological level sets the maximum pig response. An experiment was conducted with 60 crossbred (Yorkshire�Landrace sows, Yorkshire�Duroc boars; 30 barrows and 30 gilts) finishing (47.47 kg of initial weight) pigs to estimate the Optimal Biological Level (OBL) of total dietary lysine in sorghum-soybean meal diets. Total dietary lysine levels were: 0.56, 0.66, 0.76, 0.85 and 0.96%. The analyzed variables were: Average Daily Gain (ADG), Average Daily Feed Intake (ADFI), Feed Gain Ratio (FGR), Backfat Thickness (BFT), Longissimus Muscle Area (LMA), Fat Free Lean Gain (FFLG) and Plasma Urea Nitrogen concentration (PUN). The global data showed that just FFLG was affected by dietary lysine level. There was no effect of the lysine concentration on any other variable in barrows; but there PUN was affected by the dietary lysine level in gilts. The OBL to maximize FFLG (in all pigs), calculated by regression analysis, was 0.89% total lysine and the OBL to minimize PUN was 0.72% total lysine for gilts. These results confirmed that the OBL for finishing pigs to use more efficiently the dietary protein concentration will be different, upon the pig sex and the optimization criterion used.
M. Martinez , J.L. Figueroa , M.J. Gonzalez , J.L. Landero and R. Medina , 2007. Optimal Biological Level of Total Lysine for Finishing Pigs Fed Sorghum-Soybean Meal Diets . Journal of Animal and Veterinary Advances, 6: 1146-1151.