Estimation of genetic parameters for the prevalence of osseous fragments in limb joints of Hanoverian Warmblood horses.

Genetic parameters were estimated for the prevalence of osseous fragments in distal (DIJ) and proximal interphalangeal (PIJ), fetlock (FJ) and hock joints (HJ) of Hanoverian Warmblood horses by using residual maximum likelihood (REML) with linear animal models. The analyses were based on the results of 10 standardized radiographs of all four limbs of 3725 young riding horses selected for sale at auction. Transformation factors onto the underlying liability scale were verified by a simulation study. The heritability estimates of osseous fragments on the liability scale were in the range of h2 = 0.19-0.60. Further analyses of osseous fragments in FJ and HJ were performed separately in males and females. In both sexes, the heritabilities of osseous fragments in HJ were higher (h2 = 0.41 in males, h2 = 0.25 in females) than those of osseous fragments in FJ (h2 = 0.21 in males, h2 = 0.23 in females). Osseous fragments in the phalangeal joints (DIJ, PIJ, FJ) were genetically correlated moderately positive (r(g) = 0.19-0.41). The genetic correlations between osseous fragments in the phalangeal joints and in HJ were negative (r(g) = -0.27 to -0.67). Particularly, this applied to osseous fragments in FJ in both sexes, to those in front FJ in males and to osseous fragments in front and hind FJ of females (up to r(g) = -1). The heritability of height at withers was estimated at h2 = 0.27-0.28. Genetic correlations between height at withers and osseous fragments in equine limb joints were mostly moderately positive (up to r(g) = 0.75). We conclude from our results that osseous fragments in phalangeal and hock joints are genetically different traits but sex-specific expression of osseous fragments was unlikely.