The objective of this experiment was to compare the apparent total tract digestibility (ATTD) of innate fat (ether extract innate in ingredients; ENEE) versus fat added to the diet (EX) in formulations that contain increasing quantities of co-product ingredients. Results of this experiment show that diets with EX were more digestible than diets only containing ENEE. Digestion of EX (calculated by difference) showed a surprisingly large difference with ENEE much more digestible. In conclusion, fat added to the diet is much more highly digestible than innate fat which exists in the tested ingredients; therefore, energy values from fat should be estimated according to each fat source.