Effect of Increasing the SID Tryptophan:Lysine Ratio and Dietary Energy Level on Growth Performance of Growing-Finishing Pigs

Abstract The objective of this study was to evaluate the effect of increasing the SID Tryptophan:Lysine ratio in growing-finishing and dietary energy level in finishing on growth performance of growing-finishing pigs (43.6 ± 0.85 kg to 131.7 ± 2.09 kg BW). A RCBD was used with a 2 × 2 factorial arrangement of treatments: A) Dietary Energy Level: Low Energy (3,294 kcal/kg ME) vs. High Energy (3,527 kcal/kg ME) and B) SID Tryptophan:Lysine Ratio: Low Try:Lys [16%] vs. High Try:Lys [21%]. Dietary Energy Level treatment was applied from 96 kg BW to end of study and SID Tryptophan:Lysine Ratio treatment was applied throughout the study period. Diets were based on corn-soybean meal and corn coproducts and formulated to meet or exceed the nutrient requirements (NRC, 2012) for each of 4 dietary phases. A total of 1,356 pigs were housed in single-sex groups of 34 pigs (10 replicates) at a floor space of 0.63 m2/pig. Pigs had ad libitum access to feed and water. Pen was the experimental unit and data were analyzed using R version 4.0.2, with the model accounting for the fixed effects of treatment, the interaction, and the random effect of replicate. There were no treatment interactions (P > 0.05). High Try:Lys compared with Low Try:Lys increased (P < 0.05) overall ADG but had no effect (P > 0.05) on ADFI or G:F (Table 1). The High Energy treatment reduced (P < 0.05) overall ADFI and increased (P < 0.05) overall G:F compared with the Low Energy treatment. In summary, pigs fed the elevated SID Tryptophan:Lysine level had increased ADG and feeding a diet with a higher dietary energy level improved feed efficiency.