Effects of hydrolyzed chicken liver on digestibility, fecal and urinary characteristics, and fecal metabolites of adult dogs

High-protein low-carbohydrate diets have been widely used for adult maintenance dogs, as well as in specific weight loss diets and maintenance programs. However, increasing dietary protein may increase undigested protein in the hindgut, modifying intestinal fermentation and fecal metabolite concentrations. The aim of this study was to evaluate the effects of protein source and concentration on apparent total tract digestibility (ATTD) of nutrients, metabolizable energy (ME), fecal and urinary characteristics, and fecal metabolites of dogs. Twelve healthy adult dogs were distributed into six treatments (n = 6 per diet) in a balanced incomplete Latin square design consisting of three periods of 30 days each. Six diets, varying in protein source [poultry byproduct meal (PBPM) and hydrolyzed chicken liver powder (HCLP)] and concentration [24, 32, and 40% crude protein (CP) on dry matter (DM) basis] were tested: PBPM24 (PBPM based diet with 24% CP); PBPM32 (PBPM with 32% CP); PBPM40 (PBPM with 40% CP); HCLP24 (HCLP based diet with 24% CP); HCLP32 (HCLP with 32% CP); HCLP40 (HCLP with 40% CP). The ATTD of CP was greater in dogs-fed HCLP and higher protein concentrations diets (P < 0.05). However, dogs-fed HCLP diets had lower ATTD of fat and carbohydrates, and ME (P < 0.05). Similarly, high-protein diets reduced the ATTD of DM, OM, fat, carbohydrates, and energy (P < 0.05). High-protein diets increased the daily fecal output and moisture (P = 0.004 and P < 0.05, respectively), as well as the fecal score (P < 0.0001), verified as soft, moist stools, but still within the ideal range. Fecal valerate concentration was greater in dogs-fed PBPM at 32% CP (P = 0.007). Fecal isobutyrate tended to increase in dogs-fed PBPM and high-protein diets (P < 0.10). Also, dogs-fed PBPM and high-protein diets had greater fecal concentrations of isovalerate, branched-chain fatty acids (BCFA), and ammonia (P < 0.05). Finally, the fecal lactate concentration increased in dogs-fed HCLP and high-protein diets (P < 0.05). The HCLP increased the ATTD of CP, being a highly digestible protein. Although the inclusion of HCLP slightly increased fecal score and moisture, it decreased the amount of fecal metabolites of protein fermentation ammonia and BCFA, both of which are associated with proteolytic fermentation in the colon.