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) c ontaining varying ratios of insoluble:soluble fiber (I:S) on nutrient diges tibilities 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 suppleme ntal fiber (control). Ileal digestibilities of DM, OM, CP, total dietary fi ber (TDF), fat and gross energy (GE) were lower (P < 0.05) for dogs fed die ts containing supplemental fiber compared with dogs fed the control diet. F iber inclusion had a modest negative effect (P < 0.05) on total-tract DM, O M, fat and GE digestibilities compared with the control diet. Ileall digest ibilities of DM and OM by dogs fed the SH treatments responded quadraticall y (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 obser ved 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 opt imization of this ratio is desirable.