Investigation of the effects of annual vaccination on anxiety, canine cognitive dysfunction and fecal microbiota in senior dogs

It is crucial for companion animals to follow immunization protocols correctly and consistently. One of the most effective preventive strategies for a healthier population is the implementation of vaccination programs in order to eradicate infectious diseases, lower the mortality and morbidity rates of various diseases, and avoid zoonotic diseases. Today, annual vaccinations in dogs are carried out routinely and this practice typically lasts a lifetime. On the other hand, a significant gap in the literature is the lack of studies on the impact of lifelong vaccination on the brain and gut microbiome, as well as behavior, in dogs. The main goal of the thesis project, which is being supported by this project, is to shed light on the effects of vaccination age and frequency on the brain and large intestine microbiota in senior dogs (8 years and older). To this aim, in this project 16S rRNA sequencing analysis, analysis of short-chain fatty acids and flow cytometry analysis were performed to reveal the effects of age and frequency of vaccination on the brain and large intestine microbiota in senior dogs. Brain-derived neurotrophic factor (BDNF) analyzes, which have the potential to be a parameter to support anxiety and cognitive dysfunction in old dogs, which is another aim of the thesis study, were also carried out within the scope of this project. At the same time, questionnaire forms that the dog owners in the sample group answered and helped to evaluate both chronic pain and cognitive function status in dogs were used. In addition, the object discrimination test which is a memory test, was applied to evaluate the cognitive function status of the dogs. Data of the project show that there was no significant difference in the Th1/Th2 ratio between dogs vaccinated regularly every year and dogs vaccinated at least three years ago, and it was observed that annual vaccination did not affect the immune response. Additionally vaccination does not have a significant effect on BDNF levels in dogs, BDNF levels decrease with aging. Moreover, within the scope of this project, it was determined that the BDNF averages in old dogs were quite close to the BDNF averages associated with anxiety. Considering these results, it can be argued that lower than normal BDNF levels are responsible for the decrease in learning performance and the increase in anxiety in older dogs. As a result, the available data show that BDNF levels in dogs, similar to humans, are not only related to anxiety but also to aging. It was observed that 95% of the dogs participating in the study had chronic pain findings according to the Helsinki Chronic Pain Index. It was observed that annual vaccination was not effective on fecal microbiota composition in senior dogs, but Actinobacteria and Coriobacteria were found to be significantly higher (p≤ 0.05) in dogs that performed poorly in the object discrimination test. No significant difference was found between the groups in short-chain fatty acids composition with fecal samples. Although it has been shown that annual vaccination in senior dogs does not affect fecal microbiota, anxiety and cognitive dysfunction, it is thought that the increase in pain and anxiety with age should be managed and BDNF can be used as a biomarker in this process. Key words: Aging, Anxiety, BDNF, Cognitive decline, Dog