Nitrogen metabolism, macronutrient digestibility, and fecal fermentative end-products in domestic cats fed extruded, raw beef-based and cooked beef-based diets

The objective of this study was to determine differences in nitrogen (N) metabolism, nutrient digestibility, fecal and urine characteristics, and serum chemistry of domestic cats fed raw and cooked beef-based diets versus a high-protein extruded diet. Nine adult female domestic shorthair cats were utilized in a crossover design. Dietary treatments included an extruded diet [HP; ~57% crude protein (CP)], a raw beef-based diet (RB; ~53% CP), and a cooked beef-based diet (CB; ~52% CP). Cats were housed individually in metabolic cages and fed to maintain body weight. The study consisted of three 21-day periods: days 0-16 were used for diet adaptation; fecal and urine samples were collected on days 17-20; and blood samples were collected on day 21. Food intake was measured daily. During the collection phase, total feces and urine were collected. A fresh urine sample was also collected for urinalysis and acidified for N determination. In addition to total fecal collection, a fresh fecal sample was collected for determination of ammonia, short-chain fatty acid (SCFA), and branched-chain fatty acid (BCFA) concentrations. All feces were scored upon collection using a scale ranging from 1 (hard, dry pellets) to 5 (watery, liquid that can be poured). Blood was analyzed for serum chemistry. Total tract apparent dry matter (DM), organic matter (OM), CP, fat and gross energy (GE) digestibilities were higher (P<0.05) in cats fed the RB and CB versus cats fed HP. Nitrogen metabolism differed among treatments. Nitrogen intake and fecal N were lower (P<0.05) in cats fed the RB and CB versus cats fed HP, while urinary N was not different among groups. Differences were also noted in fecal fermentative end-product concentrations. Total fecal SCFA concentrations did not differ among dietary treatments; however, molar ratios of SCFA were modified by diet, with cats fed RB and CB having an increased (P<0.05) proportion of fecal propionate and decreased (P<0.05) proportion of fecal butyrate as compared to cats fed HP. Fecal concentrations of ammonia, isobutyrate, valerate, isovalerate, and total BCFA were higher (P