Quantification of Basal Endogenous Fat Losses and Their Impact on Estimates of the De Content of Dietary Fat Fed to 13 Kg and 50 Kg Pigs`

The DE system corrects GE for the energy lost in the feces, but does not correct for the energy contained in feces that is not of dietary origin. The objectives of this experiment were to quantify basal endogenous losses of fat (ELF) by feeding a fat-free diet and to calculate from this information, the underestimation of the DE content of dietary fat due to not accounting for ELF. A total of 8 barrows were utilized to determine ELF at 9.2 ± 0.6 kg and at 37 ± 2.2 kg BW. Pigs were limit-fed a daily allowance of feed estimated to be equal to 2.8 times their maintenance energy requirement. The fat-free diet (acid hydrolyzed ether extract [AEE] ≤ 0.28%) consisted primarily of corn starch, sucrose, solka floc, vitamins and minerals fed from d 0 to 10 and d 46 to 56. This provided a 7 d adaption period followed by fecal collection on d 7 to 10 and on d 53 to 56. A fully balanced diet that met all nutrient requirements was fed between the two collection periods (d 11 to 52). The ELF was calculated as the difference between the AEE provided in the feed less that recovered in the feces, reported as the mean ± the SEM and expressed as g/kg DM intake. The ELF was 4.17 ± 0.69 g/kg of DM intake at 9 kg BW and 6.67 ± 1.11 g/kg of DM intake at 38 kg BW. Based on a parallel study in which the DE content of 14 dietary fat sources were evaluated in 13 and 50 kg pigs and previously reported (Kellner et al., 2016), ELF determined herein would have accounted for 43.1% and 68.0% of the total fecal AEE at the two body weights. Not correcting for ELF in these samples resulted in underestimating dietary fat DE content by 0.42 (4.8%) and 0.60 (6.6%) Mcal/kg at 13 and 50 kg BW, respectively. Under the conditions of this experiment, the ELF was determined to be 4.17 ± 0.69 g/kg of DM intake at 9 kg BW and 6.67 ± 1.11 g/kg of DM intake at 38 kg BW. The substantial proportion of AEE contained in feces that is of ELF origin and not of dietary origin implies that the current estimates of the DE content of dietary fat are underestimated.