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Regression Analysis to Predict Growth Performance from Dietary Net Energy in Growing-Finishing Pigs
Dietary energy concentration is often altered to optimize pig growth performance and feed cost; therefore, an accurate prediction of growth performance as affected by feeding different energy concentrations is crucial. Data from 41 trials with multiple energy levels over pig’s average BW from 33 to 128 kg, extracted from 17 journal articles, 10 technical memos, and a thesis resulting in 285 observations were used in a meta-analysis. Nutrient and energy levels in all diets were estimated using the NRC (2012) ingredient library. A mixed model using experiment within trial as a random effect was used to develop a regression equations to predict ADG or G:F. Predictor variables examined for best fit models using AIC criteria included linear and quadratic terms of NE, average BW, CP, standardized ileal digestible (SID) Lys, crude fiber, NDF, ADF, fat, and ash, including their interactions. Initial best fit models included interactions between NE and CP or SID Lys. After removal of the observations (181) that fed SID Lys below the suggested requirement, these terms were no longer significant. Resulting best fit prediction equation for ADG was ADG (g) = [0.1135 × NE (kcal/kg)] + [8.8142 × average BW (kg)] – [0.05068 × average BW (kg) × average BW (kg)] + 276. Including dietary fat in the model with NE and average BW significantly improved G:F prediction model (-601 vs. -576 AIC) resulting in the best fit equation for G:F, whereas G:F = [0.000096 × NE (kcal/kg)] – [0.0025 × average BW (kg)] + [0.003071 × Fat (%)] + 0.3257. The meta-analysis indicated that, as long as diets were adequate for other nutrients (i.e., Lys), dietary NE was adequate to predict changes in ADG across a wide variety of trials with different dietary ingredients and under different environmental conditions. The analysis indicated that ADG increased by 11 g/d for every 100 kcal/kg increase in dietary NE. Also, ADG increased with heavier average BW, but decreased when average BW was above 87 kg. Furthermore, G:F improved with increasing dietary NE and fat, and decreased with increasing BW. Including dietary fat improved the fit of the equation indicating that NE may underestimate the influence of fat on feed efficiency.
Keywords: Growth performance, Pig, net energy