A metagenomic analysis of faecal microbiota in people with type 2 diabetes demonstrated that the disease was associated with marked functional alterations of the microbiota but only moderate compositional change. Future studies that employ metagenomic, transcriptomic, or metabolomics approaches could identify functional differences of the microbiota in diabetic cats that are not manifest as an overall difference in microbiota composition. The composition of the microbiota has been reported to change associated with age in humans, with the most consistent change reported being a VE-821 decreased total proportion and species diversity of bifidobacteria in elderly people. In cats, the microbiota composition is more diverse in kittens pre-weaning than postweaning. Longer term effects have not been comprehensively investigated, although one group reported no difference in bifidobacteria counts of kittens compared with geriatric cats. Specific age-associated differences in the proportions of predominant bacterial taxa or Bifidobacterium spp. were not identified in our study, although Faecalibacterium spp. were decreased in cats greater than ten years of age. Interestingly, reduced levels of Faecalibacterium spp. have also been reported in elderly humans. Further studies that compare samples from very young and very old cats may more readily identify agerelated alterations in microbiota composition of cats. None of the dietary factors that we evaluated affected faecal microbiota composition, in contrast to some previous studies which have related high protein diets to a lower abundance of Bifidobacterium. However, the diets investigated in those studies differed with respect to other nutrients as well as protein, and the effect of individual dietary components in isolation has not been scrutinised. All these previous studies have also utilised laboratory-housed cats, for which dietary and environmental factors can be more tightly controlled than for the pet cats in our study. In our study cats were fed a variety of commercially available diets, many of which were designed to meet maintenance requirements of adult cats. The variability in consumed diets also meant that only small groups of cats were available for comparison for some of the dietary factors considered, which may have impaired our ability to detect dietassociated differences. It is possible that with more extreme differences in nutrient profiles and/or studies involving larger numbers of cats, diet-related alterations in microbiota composition would become apparent. Further studies that are specifically designed to investigate individual nutrient effects are needed to ascertain the significance of diet in influencing microbiota composition in cats. In conclusion, the faecal microbiota composition of insulintreated, diabetic cats determined by 16S rRNA gene sequencing did not differ from that of non-diabetic cats in this study. qPCR identified a decrease in Faecalibacterium spp. in elderly cats, similar to observations in elderly humans. There were no differences in faecal microbiota composition associated with cat breed or gender, dietary protein, carbohydrate or fat content, or dietary formulation in our study population of pet cats.