Effects of standardized ileal digestible tryptophan: lysine ratio on growth performance of nursery pigs12

Abstract

Tryptophan is an important limiting AA in corn and soybean meal-based diets of nursery and finishing pigs (Lewis, 2000). As the availability of feedgrade AA, including Trp, increases, so does their use as replacement for intact protein sources in swine diets. The Trp requirement in swine diets can be ABSTRACT: Two experiments were conducted to estimate the standardized ileal digestible (SID) Trp:Lys ratio requirement for growth performance of nursery pigs. Experimental diets were formulated to ensure that lysine was the second limiting AA throughout the experiments. In Exp. 1 (6 to 10 kg BW), 255 nursery pigs (PIC 327 × 1050, initially 6.3 ± 0.15 kg, mean ± SD) arranged in pens of 6 or 7 pigs were blocked by pen weight and assigned to experimental diets (7 pens/ diet) consisting of SID Trp:Lys ratios of 14.7%, 16.5%, 18.4%, 20.3%, 22.1%, and 24.0% for 14 d with 1.30% SID Lys. In Exp. 2 (11 to 20 kg BW), 1,088 pigs (PIC 337 × 1050, initially 11.2 kg ± 1.35 BW, mean ± SD) arranged in pens of 24 to 27 pigs were blocked by average pig weight and assigned to experimental diets (6 pens/diet) consisting of SID Trp:Lys ratios of 14.5%, 16.5%, 18.0%, 19.5%, 21.0%, 22.5%, and 24.5% for 21 d with 30% dried distillers grains with solubles and 0.97% SID Lys. Each experiment was analyzed using general linear mixed models with heterogeneous residual variances. Competing heteroskedastic models included broken-line linear (BLL), broken-line quadratic (BLQ), and quadratic polynomial (QP). For each response, the best-fitting model was selected using Bayesian information criterion. In Exp. 1 (6 to 10 kg BW), increasing SID Trp:Lys ratio linearly increased (P < 0.05) ADG and G:F. For ADG, the best-fitting model was a QP in which the maximum ADG was estimated at 23.

Standardized ileal digestible valine:lysine dose response effects in 25- to 45-kg pigs under commercial conditions

“…The SID Lys as a percentage of the diet was reduced by 0.10 percentage points below the requirement at the expected BW by end of experiment to ensure that Lys was the second limiting amino acid throughout the experiment. This specification was based on results from a preliminary study performed in the same facility and with the same pigs as those used in experiment 1 (Gonçalves et al, 2015). This experiment indicated that diets formulated 0.10 percentage units below the SID Lys requirement estimated by NRC (2012) at the end of the experiment's weight range would ensure pigs were below the Lys requirement.…”

“…In fact, the NRC (2012) published a single overall standardized ileal digestible (SID) Val:Lys requirement of 65% for 25-to 45-kg pigs. Yet, it is possible that Val requirements to optimize different measurements of performance such as ADG, G:F, or economics may vary substantially as has been shown for other AA (Gonçalves et al, 2015). Finally, recent evidence suggests that the SID Val:Lys requirement may be greater than 65% if a broader range of BW in growing pigs is considered (Liu et al 2015;Soumeh et al, 2015).…”

An update on modeling dose–response relationships: Accounting for correlated data structure and heterogeneous error variance in linear and nonlinear mixed models1,2

“…Inc., Cary NC) data step and includes BW blocks (i.e., "Block"), SID Trp:Lys treatment (i.e., Figure 1. Example data set from Gonçalves et al (2015), which evaluated the effects of standardized ileal digestible (SID) Trp:Lys ratio on nursery pig performance with 2 residual variance groups (Var1 for [16.5 and 18.0% SID Trp:Lys ratios] and [14.5, 19.5, 21.0, 22.5, and 24.5% SID Trp:Lys ratios] for Var 2 ).…”

“…We used the data set previously presented by Gonçalves et al (2015) on G:F of nursery pigs fed experimental diets consisting of increasing levels of standardized ileal digestible (SID) Trp:Lys ratio. Briefly, data were collected under a randomized complete block design whereby 1,088 pigs arranged in pens of 24 to 27 pigs were blocked by average initial BW and randomly assigned to experimental diets (6 pens/ diet) consisting of SID Trp:Lys ratios of 14.5, 16.5, 18.0, 19.5, 21.0, 22.5, and 24.5%.…”

“…and heteroskedastic errors (Wiggans and VanRaden, 1991;Wolfinger, 1996). In fact, heterogeneity of residual variances, also known as heteroskedasticity, seems to be a relatively common phenomenon in animal production systems (Cernicchiaro et al, 2013;Gonçalves et al, 2015) and it can mislead inference if disregarded (Wiggans and VanRaden, 1991;Wolfinger, 1996).…”