Comparison of regression and fat-free diet methods for estimating ileal and total tract endogenous losses and digestibility of fat and fatty acids in growing pigs.

An experiment was conducted to 1) compare the regression and fat-free diet methods for estimating total or basal endogenous losses of fat (ELF) and fatty acids (ELFA) and true digestibility (TD) or standardized digestibility (SD) of fat and fatty acids in growing pigs and 2) compare these estimated values at the end of the ileum and over the entire intestinal tract. Ten barrows (initial body weight: 45.1 ± 2.8 kg) were surgically fitted with a T-cannula in the distal ileum and allotted to one of five experimental diets in a three-period Youden Square design. A fat-free diet was formulated using cornstarch, soy protein isolate, and sucrose. Four oil-added diets were formulated by adding four levels of soybean oil (2%, 4%, 6%, and 8%) to the fat-free basal diet at the expense of cornstarch. All diets contained 26% sugar beet pulp and 0.40% chromic oxide. Results indicated that there were no differences between true ileal digestibility (TID) of fat and true total tract digestibility (TTTD) of fat when pigs were fed soybean oil. The TID of C18:0 and total saturated fatty acids (TSFA) was greater than TTTD (P < 0.05). The total ELF at the end of the ileum were not different from that over the entire intestinal tract. In addition, total endogenous losses of C18:0 and TSFA were greater for the entire intestinal tract than at the end of the ileum, whereas total endogenous losses of C18:2 and total unsaturated fatty acids were just the opposite. Similar results were observed for basal ELF and ELFA. As the inclusion level of soybean oil increased, apparent digestibility (AD) of fat and fatty acids increased linearly (P < 0.05) except for apparent ileal digestibility of C18:0. However, SD of fat and fatty acids was not influenced by the inclusion level of soybean oil. Estimation of ELF and ELFA observed by the regression and fat-free diet methods did not differ when measured at the end of the ileal or total tract. There were no differences between the estimations of TD and SD of fat and fatty acids for soybean oil. Collectively, the estimation of TD or SD of fat can be measured over the entire intestinal tract, whereas the ileal analysis method should be used to determine the ELF, ELFA, and TD or SD of fatty acids. Correcting AD for basal ELF and ELFA can accurately estimate SD values of fat and fatty acids.