To determine true digestibility of nutrients, endogenous losses from the digestive tract must be measured. Because consistent values for endogenous losses of fat (ELF) in pigs have yet to be determined, the calculation of fat digestibility has mostly been limited to apparent digestibility.

Endogenous losses of fat may be influenced by the form of fat – extracted or intact – and by the concentration of fiber in the diet. The objective of this experiment was to determine the effect of the form of dietary fat on ileal and total tract digestibility of fat in growing pigs. To do so, it was necessary to measure endogenous losses of fat and to correct for the difference in amounts of dietary fiber in diets containing extracted fat and diets containing intact fat.