LAUSR

The aim of the present study was to evaluate the differential effect of the lysine to energy ratio on boars and gilts in the finishing phase. The effect of the standardized ileal digestible Lysine (SID Lys) to net energy (NE) ratio was analyzed in a dose-response study with 780 crossbred finishing pigs (Pietrain x (Landrace x Large White)) with an initial weight of 69.6±8.7 kg. Pigs were distributed in pens of 13 pigs, used as the experimental unit. Each pen was randomly assigned by BW and block to one of the SID Lys:NE levels (2.64, 3.05, 3.46, 3.86 and 4.27 g SID Lys/Mcal NE), with 6 replicates per dietary treatment and sex. Diets were isoenergetic (2,460 kcal NE/kg) and fed for 41 days. Individual carcass composition was measured at the end of the experiment. Statistical analysis to determine the effect of SID Lys:NE consisted on linear and quadratic polynomial contrasts. In addition, broken-line linear (BLL) models were fit when possible. Increasing the SID Lys:NE ratio had a linear (p< 0.001) and quadratic (p=0.020) effect on boars ADG. However, it did not have neither a linear nor quadratic effect on gilts ADG. Regarding FCR, increasing the SID Lys:NE ratio linearly decreased (p< 0.001) and showed a quadratic tendency in boars (p=0.055). For gilts only a linear decrease was reported (p=0.001). In addition, carcass leanness increased linearly on boars (p< 0.001) but not in gilts (p=0.097). Based on BLL modelling, growth of boars was maximized at 3.13 g SID Lys/Mcal NE (95% CI: [2.84, 3.43]) and FCR minimized at 3.95 g SID Lys/Mcal NE (95% CI: [3.46, 4.44]). The results of this experiment confirmed a differential response of boars and gilts to the lysine to energy ratio.