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This work aims at establishing dietary Lys requirements [g Lys/kg crude protein (CP, N × 6.25)] of post-weaned Iberian piglets based on responses on growth performance, carcass nutrient deposition and plasma metabolites. Sixty piglets (10.7 ± 0.1 kg initial BW) were randomly assigned into six isoenergetic diets based on corn, barley and soybean meal. Diets contained increasing Lys concentrations at a constant dietary CP content (165 ± 0.7 g/kg DM). l-Lys HCl was added at the expense of corn starch providing Lys:CP ratios (g/kg) of 43, 47, 52, 57, 64 and 72 g/kg. Other amino acids and nutrients remained constant. Six additional piglets were slaughtered at the start of the experiment to estimate initial carcass composition. Piglets were individually housed in 2 m2 pens in an environmentally controlled room until slaughter (25.3 ± 0.4 kg BW) to analyze carcass composition. Average daily gain, G:F and Gain:ME intake (g/MJ) increased linearly (P<0.001) on increasing Lys concentration. Using average daily gain as a response, the linear broken-line regression and the first derivative of the quadratic function gave the same estimation for Lys requirement (71.0 g Lys/kg dietary CP, respectively). Lysine content of dietary protein has no effect upon the apparent digestibility of DM, OM and nitrogen. Carcass protein deposition (PD) increased linearly (P<0.001) and quadratically (P<0.05) on increasing dietary Lys, reaching maximum values (39.3–40.2 g protein/d) with diets providing 57, 64 and 72 g Lys/kg CP. Carcass PD:CP intake, and carcass PD:digestible protein intake increased linearly (P<0.001) and quadratically (P<0.05) on increasing dietary Lys concentration. The linear broken-line regression using carcass PD (g/d) as response criterion estimated Lys requirement as 58.6 g Lys/kg dietary CP with a plateau PD value of 39.9 g/d. The first derivative of the quadratic function relating carcass PD and dietary Lys content gave a value of 63.7 g Lys/kg CP. Plasma urea concentration tended to decrease on increasing Lys concentration (P=0.06 and P=0.10, for linear and quadratic effects). For plasmatic urea, both linear and quadratic approach gave a similar estimate for Lys requirements, 61.2 g Lys/kg dietary CP. It is concluded that the preferred estimate based on carcass PD – the more reliable measure of metabolic Lys utilization – is 63.7 g Lys/kg CP, somewhat below the established for conventional piglets.
Lysine requirement relative to total dietary protein for optimum performance and carcass protein deposition of Iberian piglets. R. Nieto, R. Barea, L. Lara, P. Palma-Granados, J.F. Aguilera. Animal Feed Science and Technology , Volume 206 , 48 - 56 http://dx.doi.org/10.1016/j.anifeedsci.2015.05.002