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Effects of standardized ileal digestible valine:lysine ratio on growth performance of 25- to 45-kg pigs under commercial conditions
Two experiments were conducted to estimate the standardized ileal digestible (SID) Val:Lys requirement for growth performance in 25- to 45-kg pigs. In Exp. 1, 1,134 gilts (PIC 337), initially 31.2 kg ± 2.0 kg BW (mean ± SD) were used in a 19-d trial with 27 pigs/pen and 7 pens/treatment. In Exp. 2, 2,100 gilts (PIC 327), initially 25.4 ± 1.9 kg BW, were used in a 22-d trial with 25 pigs/pen and 12 pens/treatment. In both experiments, treatments were blocked by initial BW in a randomized complete block design. In Exp. 1, there were 6 treatments with SID Val:Lys at 59.0, 62.5, 65.9, 69.6, 73.0, and 75.5%. For Exp. 2, there were 7 treatments with SID Val:Lys at 57.0, 60.6, 63.9, 67.5, 71.1, 74.4, and 78.0%. Diets were formulated to ensure that Lys was the second limiting AA throughout the experiments. Responses were analyzed separately for each experiment using general linear and non-linear heteroskedastic mixed models, including initial BW as an explanatory covariate and BW block as a random effect. In Exp. 1, ADG increased linearly with increasing SID Val:Lys (P=0.009; 680, 717, 717, 712, 744, 726±17.1 g, respectively), whereas no significant treatment differences were observed for G:F (0.467, 0.467, 0.472, 0.474, 0.481, 0.472±0.0084, respectively). In Exp. 2, ADG (quadratic, P=0.002; 621, 662, 717, 708, 708, 726, 717±16.1 g, respectively) and G:F increased (linear, P<0.001; 0.415, 0.420, 0.437, 0.429, 0.433, 0.441, 0.439±0.0046, respectively) with increasing SID Val:Lys. There was no evidence of experiment by treatment interaction. Thus, data from the two experiments were combined for analysis using experiment and BW block within experiment as random effects. Competing models, namely a broken-line linear (BLL) model, a broken-line quadratic (BLQ) model, and a quadratic polynomial (QP), were compared using Bayesian information criterion (BIC). In the combined analysis, the best-fitting model for ADG was a QP (Prediction equation: –1.15 + 4.13×[SID Val:Lys] – 2.78×[SID Val:Lys]2 + 0.012×[Initial BW]) with optimum ADG estimated at 74.4% (95% CI: [69.5, >78.0%]) SID Val:Lys. The best-fitting model for G:F was also a QP (Prediction equation: –0.04 + 1.36×[SID Val:Lys] – 0.94×[SID Val:Lys]2) with optimum G:F estimated at 72.3% (95% CI: [64.0,>78.0%]) SID Val:Lys. In conclusion, 67% SID Val:Lys was able to capture 99% of maximum ADG and G:F in 25- to 45-kg pigs.
Table 1. SID Val:Lys ratio at different performance levels |
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Percent of maximum performance |
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95% |
97% |
99% |
100% |
|
ADG |
58.9 |
62.3 |
67.3 |
74.4 |
G:F |
<57.0 |
60.4 |
65.5 |
72.3 |
Keywords: growth, pig, valine