Effect of experimental methodology on fasting heat production and the net energy content of corn and soybean meal fed to growing pigs

The aim of the three experiments was to evaluated methods to predict fasting heat production (FHP) and to compare methods to determine the net energy (NE) of corn and soybean meal (SBM) fed to growing pigs. To estimate heat production (HP), pigs were housed in respiratory chambers for all experiments. In Experiment 1, six barrows (43.0 +/- 1.4 kg body weight [BW]) were fed a Corn-SBM diet for 20 d. The experimental design consisted of following periods: 7 d adaptation, 5 d ad libitum feeding, 3 d feeding at 2 x metabolisable energy (ME) for maintenance (MEm), 3 d feeding at 1 x MEm and 2 d fasting. The FHP was calculated by extrapolating HP measured at the different feeding levels to zero ME intake. The daily FHP [per kg BW0.6] determined directly after fasting for 24 h and using the regression method was 774 kJ and 694 kJ, respectively. In Experiment 2, 18 barrows (34.3 +/- 1.1 kg BW) were randomly allotted to three diets: Diet 1 contained 97.5% corn (direct NE determination of corn); diets 2 and 3 contained 25 % and 15% SBM at the expense of corn, respectively, and were used to calculate the NE of corn by difference. The NE of corn determined directly (13.21 MJ/kg DM) and by difference (13.69 MJ/kg DM) was not different. In Experiment 3, 24 barrows (36.2 +/- 1.4 kg BW) were randomly allotted to four diets to determine the effects of different basal diets on the NE content of SBM. The diets were: Basal diet 1 (97.5% corn), Test diet 1 (15% SBM at the expense of corn), Basal diet 2 (contained 72.5% corn and 25% SBM) and Test diet 2 (58% corn and 39.5% SBM). These diets were used to determine the NE of SBM using the Corn-basal diet or the Corn-SBM-basal diet, respectively. It was shown that the estimated NE of SBM did not depend on the used diet (10.04 MJ/kg and 10.62 MJ/kg DM for Basal diet 1 and 2, respectively). In summary, using the regression method to determine FHP results in lower FHP than the fasting method. There was no difference observed in the NE of corn determined directly or by difference, and different basal diets did not affect the NE of SBM.