The effect of texturized vegetable protein from soy on nutrient digestibility compared to beef in cannulated dogs

Texturized vegetable protein from soy (TVP) is widely used in canned dog foods, but its nutritional value remains in doubt. This study compared apparent prececal and total intestinal digestibility when four canned diets containing reciprocal proportions of protein from TVP (0 to 57%) and from beef (100 to 43%) were fed to eight cannulated dogs. As dietary TVP increased, the following linear changes were observed (P < 0.05): prececal and total intestinal protein digestibility decreased slightly from 77 to 71% and 86 to 80%, respectively; prececal amino acid digestibility decreased in parallel with protein; prececal carbohydrate digestibility decreased markedly from 80% to 62% and carbohydrate disappearance in the large intestine increased from 8 to 22%; prececal sodium digestibility decreased markedly (from 37 to 4%); and prececal potassium digestibility decreased (from 93 to 85%). Total intestinal digestibility of sodium and potassium decreased little (from 97 to 95% and from 98 to 97%, respectively); fecal mass and water content increased markedly (from 98 to 174 g/d and from 61 to 72%, respectively); and fat digestibility was unaffected. Prececal phosphorus digestibility from two diets containing TVP was lower than that from the all-beef diet (13 and 17%, vs 26%, P < 0.05). In conclusion, TVP is a useful source of protein in canine canned diets because amino acids from TVP are almost as digestible as those from beef in the canine intestine. Nevertheless, soy carbohydrate is poorly digested and large amounts of TVP inhibit small intestinal electrolyte digestibility and increase fecal water content.