Utility of inbreeding coefficient and sire as predictors for osteochondrosis risk in Standardbred horses

Abstract

Osteochondrosis (OC) is a developmental orthopedic disease that commonly affects young Standardbred horses and often requires surgical intervention. Both environmental and complex genetic risk factors play a role in the development of OC. However, no specific risk genes have yet been identified that could be used to quantify genetic risk at the level of the individual. Sire effects on risk of OC have been reported, but inbreeding coefficient has not been examined as predictor for genetic risk of disease. We investigated this in a cohort of 910 Standardbred yearlings fluoroscopically screened for osteochondral fragments. Controls (n = 545) were defined as horses that had no osteochondral fragments in any joint. Two groups of cases were defined; those with ostechondrosis dissecans (OCD) of the hock (n = 198) and those with plantar osteochondral fragments (POF) of the fetlock (n = 167). Horses with both hock OCD and fetlock POF were excluded. Inbreeding coefficients were obtained from a publically available database. Logarithmic regression analyses were conducted for each condition, with inbreeding coefficient, gait, and sex, +/- sire as predictors. For fetlock POF, none of the predictors were statistically significant. For hock OCD, males were slightly more likely than females to be affected (p=0.015, OR 1.5, 95% CI 1.1-2.1), while sire (p=0.0002), but not inbreeding coefficient (p=0.41) was a significant predictor (Table 1). These results suggest inbreeding coefficient in and of itself cannot be considered a proxy for genetic risk for either of the investigated conditions. Further work is needed to model the genetic risk factors underlying the influence of sire in our population.