Determination of lysine adequacy on a population basis for growing pigs

Abstract Text: Nutrient requirements are primarily determined for a growth phase and mean population without considering population variation and important variables that define population response. For lysine curves to be financially useful, responses must be established using multiple criteria and equations developed for financial modeling. This study defined the response to 4 standardized ileal digestible (SID) lysine curves using 6 population growth (whole-body, carcass) and carcass primal parameters. A total of 2048 pigs (PIC Camborough x TR-4 or 327) were used in a growth assay from 20.4 (± 0.3 kg) to 119.0 (± 1.1 kg) with a fixed time end point (110 d). Pigs were placed in 65 pens (30 to 32 pigs/pen and 0.70 m²/pig), blocked by BW and randomly allotted within gender and genotype to 4 dietary treatments, administered in 5 phases of growth (20 kg BW phases). Dietary treatments corresponded to 4 different SID lysine curves that were deviated from the 2008 PIC lysine specifications. Curves were 92, 98, 104 and 110% of the PIC standard lysine curve [SID lysine:ME (g SID lysine/Mcal ME (NCR, 1998)) = (2.7 x 10^-5 x BW²) – (0.0153 x BW) + 4.114)]. Diets were corn-soybean meal based with 15.0% corn DDGS and 2.7% choice white grease as fat source. Major ingredients were constant within diet phase, while crystalline amino acids were adjusted as required. Feed medication and ractopamine were not used. Data were analyzed as RCBD with pen as the experimental unit. Whole-body ADG improved as lysine increased (quadratic, P=0.02; 0.82, 0.85, 0.83, 0.82 kg/d for 92, 98, 104, 110% curves) as did G:F ratio (quadratic, P<0.001; 0.399, 0.418, 0.425, 0.418). Likewise, carcass G:F ratio improved as lysine increased (linear, P<0.001; 0.294, 0.303, 0.308, 0.308). The effect of increasing lysine on population growth was reflected by the reduction of the proportion of pigs sold as substandard (quadratic, P=0.014; 6.5, 3.7, 2.8, 4.3%), which improved full-value market pigs (quadratic, P=0.008, 91.2, 94.6, 95.3, and 92.9%). Carcass lean increased as lysine increased (linear, P=0.011; 52.5, 52.6, 52.6, 52.8%) as did the primal yield (n=309) relative to a 98.2 kg carcass; the latter being identical in response form to other criteria (linear, P=0.037; 87.5, 87.7, 88.0, 87.9%). This study determined the lysine curve on a population basis, using criteria not captured in interval studies. Response asymptote for each criterion was achieved at 104% of the 2008 PIC lysine requirement.

Keywords: Lysine, growing pigs, population, requirements