Heritability of metabolic traits associated with equine metabolic syndrome in Welsh ponies and Morgan horses.

Abstract

Equine metabolic syndrome (EMS) is a complex clinical disorder with both environmental and genetic factors contributing to EMS phenotypes. Estimates of heritability determine the proportion of variation in a trait that is attributable to genetics. To provide heritability estimates for nine metabolic traits associated with EMS in two high-risk breeds. Retrospective cohort study. High-density single-nucleotide polymorphism (SNP) genotype data was used to estimate the heritability (h2 SNP ) of nine metabolic traits relevant to EMS in a cohort of 264 Welsh ponies and 286 Morgan horses. Traits included measurements of insulin, glucose, non-esterified fatty acids (NEFA), triglycerides, leptin, adiponectin, ACTH, and glucose (GLU-OST) and insulin (INS-OST) following an oral sugar challenge. In Welsh ponies, seven of the nine traits had statistically significant h2 SNP estimates that were considered moderately to highly heritable (h2 SNP >0.20) including: triglycerides (0.313; s.e.=0.146), glucose (0.408; s.e.=0.135), NEFA (0.434; s.e.=0.136), INS-OST (0.440; s.e.=0.148), adiponectin (0.488; s.e.=0.143), leptin (0.554; s.e.=0.132) and insulin (0.808; s.e.=0.108). In Morgans, six of the nine traits had statistically significant h2 SNP estimates that were also determined to be moderately to highly heritable including: INS-OST (0.359; s.e.=0.185), leptin (0.486; s.e.=0.177), GLU-OST (0.566 s.e.=0.175), insulin (0.592; s.e.=0.195), NEFA (0.684; s.e.=0.164), and adiponectin (0.913; s.e.=0.181). Insufficient population size may have limited power to obtain statistically significant h2 SNP estimates for ACTH (both breeds), glucose and triglycerides in Morgans and GLU-OST in Welsh ponies. This study provides the first concrete evidence of a genetic contribution to key phenotypes associated with EMS. Eight of these nine traits had moderate to high h2 SNP estimates in this cohort. These data demonstrate that continued research for identification of the genetic risk factors for EMS phenotypes within and across breeds is warranted.