Effect of apparent ileal digestible lysine to energy ratio on performance of finishing pigs at different dietary metabolizable energy levels

A study with a total of 96 crossbred barrows and gilts fed ad libitum in a body weight range of 56-110 kg was carried out in order to investigate whether the optimum ratio of apparent ileal digestible lysine : energy (ME) depends on the energy density of the diet. Dietary treatments were ratios of 0.34, 0.42, 0.50 and 0.58 g digestible lysine/MJ ME either at an energy density of 13 or 14 MJ ME. Body weight gain as well as feed and ME conversion rate were improved when lysine : ME ratio increased from 0.34 to 0.50, whereby all parameters showed a significant ratio x sex interaction. Feed intake and feed conversion rate were higher at a dietary energy density of 13 MJ ME than at an energy density of 14 MJ ME but energy density did not influence daily growth rate, ME intake and ME conversion rate. Fat area above eye muscle and meat : fat ratio were lower and eye muscle area and lean percentage were higher at a ratio of 0.42 compared with a ratio of 0.34. Daily feed intake, body weight gain, feed conversion rate and parameters of fatness were higher in barrows than in gilts. Conversely, gilts had higher eye muscle area and lean percentage. Optimum ratio for body weight gain, feed and ME conversion rate calculated by exponential regression analysis were 0.42-0.43 in barrows. In gilts, feed and ME conversion rate were optimized at a ratio of 0.53 and 0.54. Because growth showed a linear response to increasing digestible lysine : ME ratios, optimum ratio for daily gain in gilts is considered to be at least 0.58.