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Effect of standardized ileal digestible (SID) tryptophan:lysine ratio on growth performance of 11- to 20-kg nursery pigs
Two experiments were conducted to determine the SID Trp:Lys ratio requirement for 11- to 20-kg pigs. Experiment 1 was conducted to validate the dietary approach and Exp. 2 was a dose titration. Both experiments used corn-soybean meal-based diets with 30% DDGS. Exp. 1 and 2 used 1,188 and 1,088 pigs (PIC 337×1050; initially 13.0±0.16 and 11.2±0.55 kg BW), were 21 d in duration, and had 11 and 6 pens/treatment with 24 to 27 pigs/pen, respectively. In Exp. 1, different SID Trp:Lys ratios (14.5 vs. 20%), CP (26.1 vs. 22.9%), and SID Lys levels (0.97 vs. 1.29%) combined into the following dietary treatments: High CP, High Lys, and High Trp:Lys (HHH); Low CP, High Lys, and High Trp:Lys (LHH); Low CP, Low Lys, and High Trp:Lys (LLH); and Low CP, Low Lys, and Low Trp:Lys (LLL). Lowering CP (HHH vs LHH) did not significantly influence (P>0.05) ADG, but G:F was greater in HHH compared to LHH. Decreasing lysine (LHH vs LLH) and Trp:Lys (LLH vs LLL) reduced (P<0.05) ADG and G:F, respectively. Thus, low-CP diets formulated at 0.97% SID Lys appear to ensure pigs are below their Lys requirement when determining the optimal SID Trp:Lys ratio. In Exp. 2, dietary treatments consisted of SID Trp:Lys ratios of 14.5, 16.5, 18.0, 19.5, 21.0, 22.5, and 24.5% formulated to 0.97% SID Lys and 18.1% CP. Response variables, ADG and G:F, were each fitted using general linear and non-linear mixed models with heterogeneous residual variances and pen as the experimental unit. Competing models included quadratic polynomial (QP), broken-line linear (BLL), and broken-line quadratic (BLQ). For each response, the best fitting models were selected using Bayesian information criterion. Increasing Trp:Lys increased (P<0.004) ADG and G:F in a quadratic manner. For ADG, the best fitting model was a QP [-317+7259*(Trp:Lys)–17110*(Trp:Lys)2] with maximum ADG at 21.2% SID Trp:Lys and 99% of maximum ADG achieved at 19.5% SID Trp:Lys. For G:F, BLL and BLQ models had comparable fit and estimated SID Trp:Lys requirements of 16.6 (95% CI: 16.0–17.3) and 17.1% (95% CI: 16.6–17.7), respectively. In conclusion, the SID Trp:Lys requirement for 11- to 20-kg pigs ranged from 16.6% for G:F to 21.2% for maximum ADG, with 99% of maximum ADG at 19.5% SID Trp:Lys.
SID Trp:Lys, % |
|||||||
14.5 |
16.5 |
18.0 |
19.5 |
21.0 |
22.5 |
24.5 |
|
ADG, g |
369±20.2 |
428±20.2 |
442±20.2 |
432±20.2 |
453±17.6 |
451±17.6 |
435±17.6 |
G:F |
0.543±0.008 |
0.582±0.005 |
0.582±0.005 |
0.578±0.008 |
0.590±0.005 |
0.584±0.005 |
0.580±0.008 |
Keywords: amino acids, pigs, tryptophan