Impact of the dietary inclusion of dried food residues on the apparent nutrient digestibility and the intestinal microbiota of dogs

The use of food residues for animal nutrition might imply ecological and economic advantages; however, their effects as a potential ingredient have not yet been evaluated in dogs. In the present study, four diets with 0, 5, 10 and 15% dried food residues (DFR), derived from hotel catering, were fed to 10 healthy adult dogs. At the end of each three-week feeding period, faeces and blood were collected. The apparent nutrient digestibility was calculated by the dietary inclusion of titanium dioxide as an inert marker. The results demonstrated that the apparent crude protein digestibility and ether extract digestibility decreased with increasing amounts of DFR in the diets (p < 0.05). In addition, an increase of the faecal concentrations of acetic acid, propionic acid, n-butyric acid and total short-chain fatty acids (SCFA) was observed (p < 0.05). Faecal ammonium and lactate concentrations, as well as plasma phenol and indole concentrations, were not linearly affected by the dietary inclusion of DFR. The relative abundance of Fusobacteria in the faeces of the dogs decreased, and the relative abundance of Actinobacteria and Bacteroidetes increased with increasing amounts of DFR in the diets (p < 0.05). In conclusion, the DFR seemed to be intensively fermented by the intestinal microbiota of the dogs, as indicated by the increased faecal SCFA concentrations and the shifts in the composition of the faecal microbiota. Dietary inclusion levels of up to 5% can be recommended based on our results, as the observed lower apparent crude protein and ether extract digestibility might limit the use of food residues for dogs at higher amounts.