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Productive energy (Arkansas Net Energy) value of diet and soybean meal for broilers as predicted by digestible nutrients

Martinez, D., N. Suesuttajit, C. Umberson and C. Coon

Productive energy (PE) predicts performance and economics better than N-corrected apparent metabolizable (AMEn) or classic net energy (CNE; CNE = AME – heat increment, HI). This study developed models to predict diet net energy for gain (NEg), CNE and PE, and soybean meal (SBM) PE from digestible (dig.) nutrients. 96 pens (8 blocks) with 20 chicks each were set to 12 dietary treatments: varying total dig. amino acids (TDAA; T1-T3) or dig. starch (dSt) and TDAA (T4-T6), or increasing (T7-T9; fat, TDAA) or decreasing (T10-T12; crude fiber) nutrient density. Every 7 days, one block started receiving treatment diets for one week; all were fed standard diets before. Feed was restricted to allow similar energy intake. Feed intake was recorded, body protein, fat and NEg were measured with dual-energy X-ray absorptiometry, and heat production (HP) at fasting (FHP = net energy for maintenance = NEm) and HI (HI = fed HP – FHP) in calorimetry chambers. PE was NEg + NEm. Diet AMEn, non- starch polysaccharides (total, tNSP; insoluble, iNSP; soluble, sNSP), dig. fat (dFat), dig. crude protein (dCP), dSt and TDAA were determined. Linear mixed models were fitted in JMP. A reference SBM was used to evaluate SBM PE models. Anabolic (ACPV; gain) and overall (OCPV; gain and maintenance) caloric-equivalent predictive values of dig. nutrients were calculated, defined as the number of calories for gain (NEg; ACPV) or gain and maintenance (NEg+NEm; CVO) that each g of dig. nutrient predicted. Models were validated for diet NEg (dCP, TDAA, dFat, sNSP; adjR2>0.86), CNE (dFat, dSt, tNSP, iNSP, sNSP, dSt-to-tNSP or -sNSP ratios; adjR2>0.55) and PE (dCP, TDAA, dFat, dSt, sNSP; adjR2>0.80), and for SBM PE (dCP, TDAA, dFat, dCP- or TDAA-to-tNSP ratios; adjR2>0.57). CNE was not influenced by dCP or TDAA (P>0.39). SBM PE models showed high precision (deviation ≤72 kcal/kg) and accuracy (error ≤2.2%). dCP, TDAA, and dFat explained 92, 88 and 10% of diet NEg, 85, 81, and 12% of diet PE, and 96, 96, and 0.7% of SBM PE, and showed ACPV of 4.9, 5.3, and 1.8, and OCPV of 8.4, 9.2, and 4.3 kcal/ kg, respectively. SBM contributed 44% of diet PE but 19% of AMEn.

In conclusion, models for diet and SBM PE were validated. PE, not CNE, is sensitive to dCP and TDAA and credits the actual energy value of SBM.