A decreased fertility hinders breeding aiming for healthy and sustainable dogs. The negative effect increases due to an increasing proportion of castrated dogs, and thus the breeding animals will be selected from a smaller population. In certain breeds, such as the Bernese mountain dog (BMD), the decreased fertility is a major problem, calling for strategic measures. The overall aim of the present project is to increase the knowledge of the genetic background behind the decreased semen quality in dogs. The specific aims are to: • Study the genetic background to poor semen quality in BMD using whole genome sequencing (WGS) • Use the candidate gene approach to evaluate possible presence of specific gene mutations The goal is to define the genetic background to a decreased semen quality in dogs, thereby enabling strategic measures for breeding of healthy and fertile dogs. Relevance: The results will be the basis for the possibility to include reproductive capacity in the breeding programme of the BMD, thus enabling the work for better health and welfare within this dog breed. The results will give information on the genetics behind sperm defects, of value for other dog breeds and possibly also of comparative value for other species.