How important is food structure when cats eat mice?

Feeding whole prey to felids has shown to benefit their gastrointestinal health. Whether this effect is caused by the chemical or physical nature of whole prey is unknown. Fifteen domestic cats, as a model for strict carnivores, were either fed minced mice (MM) or whole mice (WM), to determine the effect of food structure on digestibility, mean urinary excretion time of 15N, intestinal microbial activity and fermentation products. Faeces samples were collected after feeding all cats a commercially available extruded diet (EXT) for 10 days before feeding for 19 days the MM and WM diets with faeces and urine collected from d11-15. Samples for microbiota composition and determination of mean urinary excretion time were obtained from d16-19. The physical structure of the mice diet (minced or not) did not affect large intestinal fermentation as total SCFA and BCFA, and most biogenic amine (BA) concentrations were not different (P>0.10). When changing from EXT to the mice diets, the microbial community composition shifted from a carbolytic (Prevotellaceae) to proteolytic (Fusobacteriaceae) profile and led to a reduced faecal acetic to propionic acid ratio, SCFA, total BCFA (P<0.001), NH3 (P=0.04), total BA (P<0.001) and para-cresol (P=0.08). The results of this study indicate that food structure within a whole-prey diet is less important than the overall diet type, with major shifts in microbiome and decrease in potentially harmful fermentation products when diet changes from extruded to mice. This urges for careful consideration of the consequences of prey-based diets for gut health in cats.