Abstract
The objective of this study was to model the effects of standardized ileal digestible (SID) Trp:Lys ratio on growth performance of 65to 275-lb pigs. The present experiment, along with three previous experiments from Goncalves et al. (2014), were used in the analysis. For all studies, dietary treatments consisted of SID Trp:Lys ratios of 14.5, 16.5, 18.0, 19.5, 21.0, 22.5, and 24.5%. The experiments were 21 d in duration and used corn and soybean meal-based diets with 30% dried distillers grains with solubles formulated to be deficient in Lys at the end of each of the experiments. In the current experiment, a total of 975 gilts (337 × 1050; PIC, Hendersonville, TN) were used with initial BW of 234.1 ± 6.8 lb and final BW of 274.9 ± 10.4 (mean ± SD). Pens of pigs were blocked by weight and assigned to one of the seven dietary treatments in a randomized complete block design. There were 6 pens/treatment with 20 to 24 pigs per pen. For 235 to 275 lb-pigs, increasing SID Trp:Lys improved ADG (quadratic, P < 0.022), ADFI (linear, P < 0.001), and F/G (linear, P < 0.001). Data from all experiments were then combined for analysis using linear and non-linear mixed models with random effects of experiment and weight block nested within experiment allowing for heterogeneous variances. Competing models included broken-line linear (BLL), broken-line quadratic (BLQ), and quadratic polynomial (QP). In the combined analysis for ADG, QP was the best fitting model and estimated SID Trp:Lys requirement at 23.5% (95% CI: [22.7, 24.3%]). In the combined analysis for F/G, BLL and BLQ had comparable fit and estimated SID Trp:Lys requirements at 16.9% (95% CI: [16.0, 17.8%]) and 17.0% (95% CI: [15.0, 18.9%]), respectively. Thus, the estimated mean requirements for SID Trp:Lys for 65to 275-lb pigs ranged from 16.9% for optimum mean F/G to 23.5% for maximum mean ADG. Furthermore, 95% of the maximum estimated mean ADG was obtained by feeding 17.6% SID Trp:Lys and 98% of the maximum estimated mean ADG was obtained by feeding 19.8% SID Trp:Lys.
Highlights
With the increasing usage of dried distillers grains with solubles (DDGS) and feedgrade AA in commercial swine diets during the last decade, tryptophan went from being the fourth limiting AA (Naatjes et al, 20147) in corn and soybean meal-based diets to being the second or third limiting AA in diets with DDGS
The objective of this study was to model the effects of standardized ileal digestible (SID) Trp:Lys ratio on growth performance of 65- to 275-lb 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%
Summary
With the increasing usage of dried distillers grains with solubles (DDGS) and feedgrade AA in commercial swine diets during the last decade, tryptophan went from being the fourth limiting AA (Naatjes et al, 20147) in corn and soybean meal-based diets to being the second or third limiting AA in diets with DDGS. Tryptophan plays a role in a wide range of functions besides protein synthesis, with one of the most important being the synthesis of serotonin, an important regulator of feed intake (Le Floc’h et al, 20118). Recent studies suggest requirement estimates for finishing pigs ranging from 16.5 to 23.6% SID Trp:Lys (Simongiovanni et al, 20129; Salyer et al, 201310). These studies indicate the requirement may be significantly higher than suggested by NRC (2012)
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