Hydrolyzed chicken liver and increasing crude protein levels on palatability, digestibility, and intestinal fermentation products of cats

Feeding companion cats with diets based on hydrolyzed proteins may improve palatability and digestibility due to the presence of peptides and free amino acids. Furthermore, using highly digestible protein sources can decrease the undigested protein content that reaches the hindgut, thereby modifying fermentation end metabolites. This study aimed to evaluate the effects of replacing poultry byproduct meal (PBM), as the most traditional protein source for cats, with hydrolyzed chicken liver (HCL) added at 24%, 32%, and 40% of crude protein (CP) in the diet, replacing carbohydrates from brewers rice. The combination between 2 ingredients and 3 inclusions of CP permitted to test 6 extruded diets: PBM24, PBM32, PBM40; HCL24, HCL32, and HCL40. Thirty-six adult cats were arranged in a complete randomized block design to evaluate the apparent total tract digestibility (ATTD) of nutrients and energy, fermentative end products, and palatability. Crude protein ATTD increased at higher protein concentrations (P = 0.036). Fat ATTD was lower in cats fed HCL40 (P = 0.046). Carbohydrate digestibility decreased with high protein intake (P < 0.05) as a result of replacing carbohydrates with protein in the experimental diets. Gross energy ATTD was lower in cats fed HCL32 (P = 0.027). Similarly, cats fed HCL and HCL32 had lower metabolizable energy (P < 0.05) when compared to PBM. Fecal dry matter (P = 0.005) and fecal scores (P = 0.014) were lower with the inclusion of HCL (P < 0.05). Also, cats fed HCL32 had looser stools (2.61 out of a 0 to 5 score; P = 0.025), but within the acceptable range, compared to the other diets. Urinary pH increased with HCL inclusion and at higher protein concentrations (P < 0.05). Fecal acetate, propionate, valerate, total short-chain fatty acids (SCFA), isovalerate, and total volatile fatty acids (VFA) were higher in cats fed HCL compared to those fed PBM (P < 0.05). In the palatability test, cats mostly preferred diets based on HCL and with higher protein concentrations, mainly HCL40, over those based on PBM (Power test >0.75). The replacement of PBM by HCL in diets was highly accepted and improved the fermentative end metabolites associated with intestinal functionality in cats, especially SCFA.