Comparison of Four Digestibility Markers to Estimate Fecal Output of Dogs

The use of chromic oxide is the standard marker for determining digestibility of dog diets. However, this method is not without issue regarding safety and repeatability. Therefore, it was our objective to determine the effect of using alternative markers to estimate fecal output and calculate diet digestibility. Four dietary treatments were produced from sorghum fractions (WSD, whole sorghum diet; FLD, sorghum flour diet; MFD; sorghum mill-feed diet) and rice, corn, wheat 1:1:1 (CON, control) as starch sources, and fed to twelve Beagle dogs in a 4 x 4 replicated Latin square design. Fecal output was estimated using external markers Cr₂O₃ (0.25%) and TiO₂ (0.40%) mixed with the diet prior to extrusion, acid insoluble ash (AIA) as an internal marker, and by total fecal collection (TFC). Fecal output of OM, DM, CP, GE, crude fiber, and crude fat by the 4 different methods were analyzed and compared using Pearson partial correlation coefficients from the Error SSCP Matrix. Correlations (R²) were considered significant at P < 0.05. The TiO₂ and Cr₂O₃ were highly (P < 0.05) correlated for estimates of fecal output of all nutrients: 0.93, 0.91, 0.91, 0.91, 0.99, and 0.93 for OM, DM, CP, crude fat, crude fiber and GE, respectively. The TiO₂ also had significant correlations (P < 0.05) to TFC (0.59, 0.55, 0.61, 0.61, 0.82, and 0.60 for OM, DM, CP, crude fat, crude fiber and GE, respectively) and AIA (0.84, 0.82, 0.82, 0.82, 0.84, and 0.86 for OM, DM, CP, crude fat, crude fiber and GE, respectively). The Cr₂O₃ was also correlated (P < 0.05) to TFC (0.56, 0.50, 0.57, 0.57, 0.81, and 0.56 for OM, DM, CP, crude fat, crude fiber and GE, respectively) and AIA (0.75, 0.71, 0.73, 0.73, 0.79, and 0.78 for OM, DM, CP, crude fat, crude fiber and GE, respectively). The TFC and AIA methods had the poorest correlation among estimates of fecal outputs of OM, DM, CP, crude fat, crude fiber and GE (0.29, 0.22, 0.33, 0.33, 0.54, and 0.33, respectively). Within these nutrients, only TFC and AIA for crude fiber fecal output correlated (P<0.05). The study suggests that TiO₂ may be a better marker to estimate fecal output in dogs than Cr₂O₃. TiO2 is considered GRAS and is a common colorant in pet foods. The use of AIA technique needs to be further studied, since it represents a potential option for evaluating diets that are difficult to incorporate external markers.