This doctoral thesis focused on feline diabetes mellitus (DM) in Germany. The aim was to provide an overview of the regional characteristics of the disease by determining frequency, signalment, laboratory changes, concurrent diseases, therapy and monitoring of DM in cats. Such information might allow an optimisation of the management of feline DM in Germany, where needed. For data collection, a retrospective (publication 1) and a prospective study (publication 2) were conducted. In the retrospective part, the frequency of DM was assessed by evaluating 129,505 laboratory submissions to Antech Lab Germany GmbH (formerly SYNLAB Vet GmbH) between 2015 and 2018 in addition to signalment and laboratory results. Due to a very large sample size, effect sizes r and Cramér V were evaluated in addition to the significance level, which was defined as p < 0.05 throughout this thesis. In the prospective study, blood samples from 144 diabetic cats (newly diagnosed and previously treated) were analysed at Antech Lab Germany GmbH (formerly SYNLAB Vet GmbH) between May 2021 and July 2022. Based on laboratory data and an additional completed questionnaire, signalment, laboratory findings (including serum cobalamin concentration requiring supplementation), the occurrence of suspected concurrent diseases (including hypersomatotropism, pancreatitis, hyperthyroidism) and the management of feline DM were examined. The prevalence of DM was 7.2%. This significantly higher value compared to other countries may be due to the fact that in this doctoral thesis the frequency of the disease was determined among laboratory submissions and likely mainly sick animals and also older cats (median age at the time of laboratory submission: 12 years) were examined. However, a higher regional prevalence of DM in Germany when compared to other countries cannot be ruled out. The prospective part also confirmed that most commonly older cats are affected (median age at diagnosis: 11 years). Despite an overrepresentation of male animals (retrospective 59.4%, prospective 66.4%), sex and neutering could not be classified as a relevant risk factors due to the very small effect size in the retrospective part. Laboratory abnormalities in cats with DM identified in this study primarily include lipid derangements (hyperlipidaemia) and increased liver enzyme activities. These appear more pronounced in poorly controlled diabetics and may indicate hepatic lipidosis as part of the underlying disease. The findings are consistent with information found in the literature and were confirmed by this large-scale study. Furthermore, the results suggest that comorbidities are common in cats with DM. In the prospective study, there was laboratory evidence of pancreatitis in 54.2% and hypersomatotropism in 17.5% of diabetic cats. Hyperthyroidism occurred less frequently with 5.8%, although a possible effect of euthyroid sick syndrome has to be discussed. The results are comparable to studies from other countries. In addition, serum cobalamin concentration requiring supplementation was identified in 24.5% of diabetic cats in the prospective study. To the author's knowledge, cobalamin status has not been examined in cats with DM so far. Regarding the therapy and management of feline DM, these are largely based on the currently available guidelines. In conclusion, cats with DM should not only be routinely tested for concurrent diseases (including pancreatitis, hypersomatotropism, hyperthyroidism), but the serum cobalamin concentration should also be included in this work-up.
