Effect of Hydrolyzed Frozen Meat on Diet Palatability, Apparent Digestibility, Immune Response, Fecal Microbiota, and Metabolome in British Shorthair Cats

Frozen meat is an important source of protein in pet food, and has attracted much attention in recent years. In this study, we compared the effect of meat meal (MM), frozen meat (FM), and hydrolyzed frozen meat (HFM) as ingredients in extruded pet food on its palatability and apparent digestibility, as well as its effects on the immune response, fecal microbiota, and metabolome of British shorthair cats. A total of 24 British shorthair cats were allocated to the MM, FM, and HFM groups according to body weight and gender. The palatability test lasted 4 days and the feeding test lasted 45 days. The results showed that the FM and HFM diets had better palatability than the MM diet (p < 0.05) and significantly improved dry matter and crude protein digestibility (p < 0.05). The serum IL-10 level was significantly higher in the HFM group compared to the MM and FM groups (p < 0.05). The serum IgM levels were also found to be significantly higher in the FM group compared to the MM and HFM groups (p < 0.05). The blood urea nitrogen/creatinine ratio was significantly lower in the HFM and FM groups than in the MM group (p < 0.05). Cats fed HFM had a higher abundance of fecal Actinobacteria and Bifidobacterium and a lower content of Bacteroidota (p < 0.05). Furthermore, serum metabolomics analysis revealed that the tryptophan (Trp) metabolism and bile acid metabolism were affected by HFM. Overall, FM and HFM were better for the cat’s health than meat meal, but they also have some potential risks.