Genetic factors of equine osteochondrosis and fetlock osteochondral fragments: A scoping review - Part 2.

Equine osteochondrosis and osteochondral fragments in the fetlock joint are linked to various environmental and genetic risk factors. To assess the scope of the literature linking these risk factors to the development of these osteochondral disorders, while identifying knowledge gaps and challenges to guide future research, a scoping review was performed. This article constitutes the second part of this scoping review and focuses on genetic factors, with the first part addressing environmental factors. To identify potentially relevant papers, online bibliographical databases PubMed and Web of Science were utilised, supplemented with articles listed on the OMIA website (OMIA:000750-9796). After collecting entries, removing duplicates, screening titles, abstracts, and full-text documents for eligibility, and manually searching reference lists of the remaining articles, a total of 212 studies were identified for this scoping review. First, a brief overview of the etiopathogenesis of equine osteochondrosis and osteochondral fragments in the fetlock joint is provided. Subsequently, this article delves into the genetic aspects by presenting an overview of significantly associated quantitative trait loci and potential candidate genes. Next, the challenges in both phenotypic and genomic selection against these osteochondral disorders are discussed, with a focus on the difficulties in phenotyping, the establishment of large and representative reference populations, publication bias, lesion-specific heritabilities, and studbook policies. In conclusion, while there is considerable potential to implement preventive measures that can alleviate the economic burden and enhance animal welfare, further research is necessary. This research should utilize precise and standardized phenotype definitions applied across studies with preferably larger populations.