Evaluation of methods for estimation of the net energy content of pig feeds

The net energy (NE) content of the feed strongly determines pig performances, so that an accurate and rapid estimation is very important. We designed an experiment to evaluate the use of feed tables, chemical analyses and in vitro organic matter digestibility (OMd) for the prediction of the in vivo NE. 20 compound feeds with variable nutrient and/or ingredient composition were formulated and each feed was fed to six pens of three pigs in three weight intervals at an initial mean life weight of 52, 72 and 94 kg, respectively. The faeces were spotsampled during five days and nutrient digestibility was determined using acid insoluble ash as marker. The compound feeds as well as their ingredients were analysed for chemical composition and in vitro OMd according to Boisen and Fernandez (1997). The in vivo NE content of the feeds was calculated according to the Dutch feed evaluation system (CVB,2016) and amounted to 10.84 ± 0.92 MJ/kg DM (mean ± sd), varying from 8.31 to
12.01 MJ/kg DM. The sd of the NE due to variation between pens averaged 0.08 MJ/Kg DM and was mainly caused by the differences in weight interval. The calculated NE content increased with 0.0021 MJ/kg DM per kg bodyweight. Besides, the NE content of the 20 feeds was calculated from the NE of the composing ingredients, using either directly the tabular NE-values or the analyzed proximate composition in combination with the tabular digestion coefficients, which resulted in a prediction error of 0.34 and 0.19 MJ/kg DM, respectively. Further, multiple regression equations were developed using chemical parameters and in vitro OMd. The best equation based on chemical parameters (crude fat, starch, ADL and crude ash) resulted in an error of 0.13 MJ/kg DM, whereas the incorporation of in vitro OMd could slightly lower this error (0.11 MJ/kg DM).