Impaired Reproductive Function in Equines: From Genetics to Genomics

SIMPLE SUMMARY: The genetic origins behind reproductive traits are still far from clear: this is especially true in horses, where the lack of objective reproductive phenotypes (particularly in mares) reduces the quantity of information available. However, in recent years, the study of genomics has produced a notable increase in our knowledge of genetic causes of reproductive impairment in the species. In this paper, we review the recent advances and studies analyzing genomic mechanisms affecting the reproductive function in mares and stallions. ABSTRACT: Fertility is one of the key factors in the economic and productive success of the equine industry. Despite this, studies on the genetic causes affecting reproductive performance are scarce, especially in mares, where the genetic architecture of the reproductive traits is extremely complex. Today, with the increasing availability of new genomic methodologies for this species, we are presented with an interesting opportunity to understand the genetic basis of equine reproductive disorders. These include, among others, novel techniques for detecting chromosomal abnormalities, whose association with infertility in horses was established over 50 years ago; new sequencing technologies permitting an accurate detection of point mutations influencing fertility, as well as the study of inbreeding and molecular homozygosity, which has been widely suggested as one of the main causes of low reproductive performance in horses. Finally, over the last few years, reproductive performance has also been associated with copy number variants and candidate genes detected by genome-wide association studies on fertility traits. However, such studies are still scarce, probably because they depend on the existence of large and accurate phenotypic datasets of reproductive and/or fertility traits, which are still difficult to obtain in equines.