The ratio of insoluble to soluble fiber components in soybean hulls affects ileal and total-tract nutrient digestibilities and fecal characteristics of dogs.

An experiment was conducted to evaluate the effects of soybean hulls (SH) containing varying ratios of insoluble:soluble fiber (I:S) on nutrient digestibilities and fecal characteristics of dogs. Ileally cannulated dogs (n = 6) were fed seven diets in a 6 x 7 Youden square arrangement of treatments. The seven diets included five SH-containing diets with I:S of 1.9, 2.7, 3.2, 5.2 or 7.2 and two diets containing either beet pulp (BP) or no supplemental fiber (control). Ileal digestibilities of DM, OM, CP, total dietary fiber (TDF), fat and gross energy (GE) were lower (P < 0.05) for dogs fed diets containing supplemental fiber compared with dogs fed the control diet. Fiber inclusion had a modest negative effect (P < 0.05) on total-tract DM, OM, fat and GE digestibilities compared with the control diet. Ileal digestibilities of DM and OM by dogs fed the SH treatments responded quadratically (P < 0.05) to I:S, with digestibility coefficients decreasing as the I:S approached 3.2. Highest ileal digestibilities were observed for diets with an I:S of 1.9 and 7.2. Similarly, a quadratic response (P < 0.05) was observed for digestibility of total amino acids at the ileum. Fecal outputs were lower (P < 0.001) when dogs consumed the control diet vs. fiber-containing diets. Among the SH-containing diets, there was a linear increase in fecal output as I:S increased (P = 0.031). The I:S in the diet affects DM and OM digestibilities at the ileum and affects fecal output, indicating that optimization of this ratio is desirable.