This observation is Regorafenib common to both genetic and diet-induced models of obesity, and has also been shown to be reversible with weight loss. Similarly, obesity in humans has been associated with an increased proportion of Firmicutes and a decreased proportion of Bacteroidetes. Weight loss, achieved by either diet or bariatric surgery, was inversely correlated with the proportion of Bacteroidetes in two studies. However, a proportional shift in the opposite direction has also been reported in obese humans, as has no difference in the relative proportions of these phyla. In this latter study, although the proportions of Firmicutes and Bacteroidetes were not different between obese and lean people, faecal short chain fatty acid concentration was significantly higher in the obese group. This observation indicates that there may be functional differences in the microbiome associated with obesity, and that these differences can occur independently of compositional differences. The composition of the microbiota of mice with type 2 diabetes mellitus is also reported to be altered, with an increase in the ratio of Bacteroidetes to Firmicutes being associated with this disease in a mouse model of type 2 diabetes mellitus without obesity. Similar differences in microbiota composition of humans with type 2 diabetes mellitus have been identified, with a reduced proportion of Firmicutes and a positive correlation between the ratio of Bacteroidetes to Firmicutes and plasma glucose concentration described in one study. Diabetes mellitus is a common endocrinopathy in cats, with an estimated incidence of 0.5% in first opinion veterinary practice. There are two pathophysiological components of feline diabetes mellitus: reduced insulin secretion from dysfunctional and/or lost pancreatic beta cells, and insulin resistance, making this disease analogous to type 2 diabetes mellitus in humans. No studies of the gastrointestinal microbiota of diabetic cats have previously been published. The aims of this study were to compare the faecal microbiota composition of diabetic and non-diabetic cats, and secondarily to determine if host signalment and dietary factors influence the composition of the faecal microbiota in cats. In general, there is agreement that Firmicutes, Actinobacteria and Bacteroidetes are dominant bacterial phyla in feline faecal samples. However, descriptions of the feline microbiota vary between studies, likely as determination of the relative abundances of bacteria is influenced by sample population, the sample handling, and also the molecular technique that is employed. Actinobacteria was determined to be the most prevalent bacterial phylum in feline faecal samples when an alternative target gene gene) was amplified for sequencing, and when investigated by fluorescent in situ hybridisation. Inter-laboratory differences in DNA extraction, sample handling, and storage protocols are also potential sources of variation between studies. Further confounding interpretation of results is the fact that the composition of the microbiota varies along the gastrointestinal.