Abstract Lysine is the first limiting amino acid in typical corn–soybean meal diets for pigs, and its ratio to dietary energy is critical for maximizing lean tissue growth. Optimizing the standardized ileal digestible (SID) lysine-to-metabolizable energy (Lys:ME) ratio may enhance both biological efficiency and economic return under commercial conditions. This study evaluated the effect of increasing SID Lys:ME ratios on growth performance, feed efficiency, and profitability of grow-finish pigs. The experiment was conducted at the Iluma Alliance Research and Validation Center using commercial crossbred PIC 337 pigs housed in group pens with similar initial body weight and equal numbers per pen. Diets were formulated to provide incremental levels of SID lysine while maintaining constant metabolizable energy within each phase. In Experiment 1, pigs were assigned to one of six dietary treatments with increasing SID lysine concentrations, and performance was measured from 30 to 120 kg body weight. In Experiment 2, phase-specific nutritional profiles were evaluated from 30 to 60 kg (growing 1), 60 to 80 kg (growing 2), and 80 to 120 kg (finishing). Each experiment followed a randomized complete block design, blocking by initial weight and sex. Data were analyzed using a linear mixed-effects model (lmer function in R), including treatment as a fixed effect, pen size as a covariate, and block as a random effect. Differences among least-square means were considered significant at P ≤ 0.05. Increasing dietary SID lysine improved (P ≤ 0.05) average daily gain (ADG) and tended to enhance feed conversion ratio (FCR) without affecting daily feed intake. Across phases, each 0.1-percentage-point increase in SID lysine resulted in an additional 0.5 to 1.2 kg of final body weight, depending on the growth stage. Pigs fed the highest Lys:ME ratios exhibited more than 5% greater weight gain than the control group, particularly during the late finishing phase. Enhanced amino acid density improved growth performance without negatively affecting feed efficiency, indicating that pigs utilized the additional lysine to support lean tissue accretion rather than excess feed consumption. Economic evaluation showed that the increased feed cost was compensated by improved conversion and carcass yield, resulting in up to 10% higher net profit per pig in the highest-lysine treatment compared with the control. In conclusion, elevating the SID Lys:ME ratio improved growth rate and profitability of grow-finish pigs without affecting feed intake. Nutritional profiles with higher digestible lysine levels optimized performance, particularly in heavier pigs, supporting the upward adjustment of lysine recommendations to maximize biological efficiency and economic return in modern PIC 337 genetics.
Martínez‐Gómez et al. (Wed,) studied this question.