Digestible methionine plus cystine to digestible lysine ratio in diets supplemented with ractopamine for finishing pigs

The experiment was carried out to determine digestible methionine + cystine: digestible lysine (Met + Cys/Lys) ratio for barrows selected for deposition of lean meat in the carcass supplemented with ractopamine (RAC) in the finishing phase. Sixty-four barrows with 84.68 +/- 1.34 kg BW was allotted to an experimental randomized block design, fed diets containing four Met + Cys/Lys ratio (0.54, 0.58, 0.62 and 0.66) supplemented with ractopamine, eight replications, during a period of 28 days. Met + Cys/Lys did not affect feed intake, average daily gain, feed conversion, fat thickness, lean meat amount, carcass weight, lean meat percentage and carcass yield of pigs. Met + Cys/Lys ratio influence quadraticaly the concentrations of total cholesterol in the loin and linearly the cholesterol concentrations in the subcutaneous fat. The lowest levels of total cholesterol were observed in pigs fed diet with 0.66 Met + Cys/Lys ratio. In pigs from 85 to 109 kg supplemented with ractopamine, the 0.54 Met + Cys/Lys ratio meets the requirement for better performance and better carcass traits, while to lower the cholesterol levels in the loin and subcutaneous fat the requirement is 0.66 Met + Cys/Lys ratio.