Osteochondrosis in the tarsocrural joint and osteochondral fragments in the fetlock joints in Standardbred trotters. II. Heritability

Abstract
Summary: The progeny (N=793) of 24 Swedish Standardbred trotter stallions were used for genetic studies on radiographic findings of osteochondrosis (OC) in the tarsocrural (hock) joint and palmar/plantar osteochondral fragments (POF) in the metacarpo‐ and metatarsophalangeal (fetlock) joints.Twenty stallions were drawn at random from the population of Swedish Standardbred trotter stallions approved for breeding, and 4 stallions were selected for their own OC and POF status. The progeny groups included 28–39 investigated yearlings per stallion. About half of the horses were born in each of the years 1988 and 1989.Hock joint OC was diagnosed in 71 (10.5%) and fetlock joint POF in 145 (21.5%) offspring of the randomly selected stallions. The incidence of OC and POF varied among the progeny groups between 0–24% and 11–44% respectively (P<0.05). The findings were analysed as all‐or‐none traits and as sire‐offspring regressions. Non‐genetic effects of sex, age at examination and year/month of birth were simultaneously considered with genetic effects of sire. The heritability was estimated to be 0.08–0.09 on the threshold scale for both traits, corresponding to 0.24–0.27 for OC and to 0.17–0.19 for POF on the underlying quantitative scale. Sire‐offspring regressions yielded heritabilities of 0.34 and 0.23 for OC and POF, respectively.Correlations between OC and POF, as well as between these and measures of body size, were contradictory, probably due to the limited amount of data and the all‐or‐none characters of both OC and POF. However, we conclude that the predisposing factors of OC and POF are inherited independently of each other.