Endogenous fat loss and true total tract digestibility of poultry fat in adult dogs

: Fat plays an important role in the carnivore diet. It has high digestibility and high energy content and likely improves digestibility of the diet when present in greater amounts, suggesting that endogenous fat adversely affects the apparent digestibility of fat in low-fat diets. This study aimed to determine the endogenous fat loss (EFL) and true total tract digestibility (TTTD) of fat in dogs by using diets having different fat:carbohydrate ratios. Furthermore, the apparent total tract digestibility (ATTD) of macronutrients and energy, food intake, fecal output, and stool quality were evaluated. Twelve adult Beagle dogs were stratified into three 10-d periods in a 6 × 3 balanced incomplete Latin square design. Dietary treatments included a low-fat basal diet (3.4% fat) supplemented with 6 poultry fat levels (1, 4, 10, 12, 16, or 20%). The dogs were individually housed in metabolic cages and fed to meet the maintenance energy requirements. The ME intake was similar across the diets, despite the clearly low palatability of the 1 and 4% fat diets. Dietary ATTD of DM, OM, fat, and GE were improved after fat inclusion ( 0.05). The amount of fecal output decreased with increasing level of fat in the diet, but the fecal score was not affected. The stool quality was close to ideal (2.4-2.8) and no different among diets. The EFL was estimated using 2 regression methods and was expressed as 155 mg∙kg BW∙d or 7.9 g/kg of DMI. The TTTD of poultry fat was the same irrespective of the dietary fat level. Poultry fat was 99.3% digestible for the dogs. The relation between EFL and fat intake was higher for the lower-fat diets, explaining the ATTD of fat increase according to the dietary fat inclusion. In conclusion, dietary fat is well digested by dogs irrespective of the level included, close to 100%. The ATTD of fat in low-fat diets is underestimated because the endogenous content is proportionally greater than that in high-fat diets.