Heritability estimation of osteochondrosis dissecans in Maremmano horses

The heritability of radiographic findings of osteochondrosis dissecans (OCD) and its effect on the frequency of this disease under different selection strategies were estimated in a population of Maremmano horses. Three hundred and fifty offspring of 75 sires were examined: all 3-year-old animals clinically evaluated for admission to the Performance Test from 1993 to 1998 and a sample of 2-year-old horses. The clinical procedure included radiographic examination of the tibio-tarsal, the femoro-patellar, and the metacarpo-phalangeal joints. The heritability was analyzed by two statistical methods: a threshold animal model based on the underlying liability concept and an animal model on the 0–1 observable scale. The h2 estimate ranged between 0.09 and 0.14 for the first and second method, respectively. Also, the efficiency of different selection strategies on the prevalence of OCD was tested on this basis. The simulated results indicate that the incidence of osteochondrosis in the Maremmano population could be reduced; active selection, simulating five generations, for both stallions and mares reduced the frequency of OCD from 16 to 2%.