Exploratory factor analysis of signalment and conformational measurements in Thoroughbred horses with and without recurrent laryngeal neuropathy

Ten years of the horse reference genome: insights into equine biology, domestication and population dynamics in the post-genome era

The horse reference genome from the Thoroughbred mare Twilight has been available for a decade and, together with advances in genomics technologies, has led to unparalleled developments in equine genomics. At the core of this progress is the continuing improvement of the quality, contiguity and completeness of the reference genome, and its functional annotation. Recent achievements include the release of the next version of the reference genome (EquCab3.0) and generation of a reference sequence for the Y chromosome. Horse satellite‐free centromeres provide unique models for mammalian centromere research. Despite extremely low genetic diversity of the Y chromosome, it has been possible to trace patrilines of breeds and pedigrees and show that Y variation was lost in the past approximately 2300 years owing to selective breeding. The high‐quality reference genome has led to the development of three different SNP arrays and WGSs of almost 2000 modern individual horses. The collection of WGS of hundreds of ancient horses is unique and not available for any other domestic species. These tools and resources have led to global population studies dissecting the natural history of the species and genetic makeup and ancestry of modern breeds. Most importantly, the available tools and resources, together with the discovery of functional elements, are dissecting molecular causes of a growing number of Mendelian and complex traits. The improved understanding of molecular underpinnings of various traits continues to benefit the health and performance of the horse whereas also serving as a model for complex disease across species.

Identification of loci affecting sexually dimorphic patterns for height and recurrent laryngeal neuropathy risk in American Belgian Draft Horses

Equine recurrent laryngeal neuropathy (RLN) is a bilateral mononeuropathy with an unknown etiology. In Thoroughbreds (TB), we previously demonstrated that the haplotype association for height (LCORL/NCAPG locus on ECA3, which affects body size) and RLN was coincident. In the present study, we performed a genome-wide association scan (GWAS) for RLN in 458 American Belgian Draft Horses, a breed fixed for the LCORL/NCAPG risk alelle. In this breed, RLN risk is associated with sexually dimorphic differences in height, and we identified a novel locus contributing to height in a sex-specific manner: MYPN (ECA1). Yet this specific locus contributes little to RLN risk, suggesting that other growth traits correlated to height may underlie the correlation to this disease. Controlling for height, we identified a locus on ECA15 contributing to RLN risk specifically in males. These results suggest that loci with sex-specific gene expression play an important role in altering growth traits impacting RLN etiology, but not necessarily adult height. These newly identified genes are promising targets for novel preventative and treatment strategies.