Genetic parameters for osteoarthrosis, radiographic changes of the navicular bone and sidebone, and their correlation with osteochondrosis and osteochondral fragments in Hanoverian warmblood horses

In the present study, results of radiographic examinations were used for estimation of genetic parameters for osteoarthrosis (OA) in distal interphalangeal joints, proximal interphalangeal joints, fetlock, hock and stifle joints, radiographic changes in the navicular bones of the forelimbs (RCNB) and sidebone in 7396 Hanoverian Warmblood horses. Radiographic changes were recorded as ordinal traits in dependence of the number of joints affected or, in case of RCNB, of their severity score. In addition, their genetic correlations with osteochondrosis (OC) and osteochondrosis dissecans (OCD) in fetlock, hock and stifle joints as well as palmar/plantar osteochondral fragments (POFs) and dorsodistal osteochondral fragments in fetlock joints were determined. The prevalence for OA in hock joints was 21.4%, for OA in fetlock joints 7.4%, for RCNB 33.6% and for sidebone 9.6%. Horses with OA in most cases were affected at only one limb while RCNB and sidebone in most cases were found bilaterally. The heritabilities estimated in a linear animal model and transformed onto the liability scale were at 0.17 for OA in fetlock joints, 0.40 for OA in hock joints, 0.19 for RCNB and 0.59 for sidebone. Additive genetic correlations among OA in fetlock joints, OA in hock joints, RCNB and sidebone were moderate (rg=−0.19 to rg=0.18). The highest additive genetic correlations were found between OA in fetlock joints and OC in fetlock joints (rg=0.71) as well as OCD in fetlock joints (rg=0.62). RCNB showed positive genetic correlations with OC and OCD in the different joints as well as with OFs in hock and stifle joints. POFs and RCNB were genetically negatively correlated. The size of the heritability estimates for OA in fetlock joints, OA in hock joints, RCNB and sidebone seems to be sufficient high that breeding measures can be recommended in order to reduce their prevalence.