Effect of standardized ileal digestible (SID) tryptophan:lysine ratio on growth performance of finishing pigs

Abstract Text:

Four experiments were conducted to estimate the SID Trp:Lys ratio requirement for finishing pigs. Dietary treatments consisted of SID Trp:Lys ratios of 14.5, 16.5, 18.0, 19.5, 21.0, 22.5, and 24.5%. All experiments were 21 d in duration and used corn-soybean meal-based diets with 30% DDGS formulated to be deficient in Lys at the end of each experiment. A total of 1,166, 1,099, 1,132, and 975 gilts (PIC 337×1050, initially 29.9±2.0, 55.5±4.8, 71.2±3.4, and 106.2±3.1 kg BW±SD) were used in Exp. 1 to 4, respectively. Within each experiment, pens of pigs were blocked by weight and assigned to one of the 7 dietary treatments in a randomized complete block design. Each experiment consisted of 6 pens/treatment with 20 to 28 pigs/pen. Data from all experiments were combined for analysis using general linear and non-linear mixed models with random clustering effects of experiment and weight block within experiment and also with pen as the experimental unit. Competing models included quadratic polynomial (QP), broken-line linear (BLL), and broken-line quadratic (BLQ). Best fitting models were selected using Bayesian information criterion. Increasing Trp:Lys increased ADG and G:F in a quadratic manner (P<0.001). For ADG, QP [Prediction equation: 189.5+6084*(Trp:Lys)–12878*(Trp:Lys)²] and BLQ [if SID Trp:Lys <22.9%, prediction equation: 900–15000*(0.229–Trp:Lys)²] had comparable fit and estimated SID Trp:Lys requirements at 23.6 (95% CI: 21.2–26.1%) and 22.9% (95% CI: 22.0–23.7%), respectively. For G:F, BLL [if SID Trp:Lys <16.9%, prediction equation: 0.4036–1.0*(0.169–Trp:Lys)] and BLQ [if SID Trp:Lys <18.7%, prediction equation:  0.403–15.0*(0.187–Trp:Lys)²] had comparable fit and estimated SID Trp:Lys requirements at 16.9 (95% CI: 16.0–17.9) and 18.7% (95% CI: 18.1–19.3%). Thus, the estimated mean requirements for SID Trp:Lys for 30 to 125 kg pigs ranged from 16.9% for G:F to 23.6% for maximum ADG.  Furthermore, 95% of the maximum estimated ADG was obtained feeding 17.5% SID Trp:Lys and 98% of the maximum estimated ADG was obtained feeding 19.5% SID Trp:Lys.

Keywords: amino acids, finishing pigs, tryptophan