Standardized ileal digestible lysine in diets for pigs fed ractopamine in commercial production system

Two consecutive experiments were conducted using 480 pigs each with six replicate pens per treatment and 10 pigs per pen to evaluate the effect of standardized ileal digestible (SID) Lys (0.81, 0.91, 1.01, and 1.11%) in diets containing ractopamine (RAC; 10 or 20 mg kg-1) on growth and carcass traits of barrows in a commercial production system. There were no effects of either RAC levels or the interaction between RAC and SID Lys levels on any of the performance and carcass variables. No lack of fit was detected in the response surface analysis. From d 0 to 21, there was no effect of SID Lys levels on ADFI. However, as SID Lys increased, there was a linear increase in ADG and G:F. As SID Lys increased, the ADG, G:F, loin depth, and lean percentage improved linearly from d 0 to 28, with no effect on ADFI and backfat thickness. In conclusion, performance and carcass traits of pigs fed RAC (10 or 20 mg kg-1) in a commercial finishing facility are improved by up to 1.11% SID Lys supplementation. There is no additional benefit of feeding 20 mg kg-1 RAC in comparison with 10 mg kg-1 RAC