Estimates of heritability for ossification of the cartilages of the front feet in the Finnhorse.

Abstract

Ossification of the cartilages in the foot is common in coldblooded horses, but prevalence as well as ossification pattern varies between breeds; research on estimation of heritability for the condition has been limited. Our purpose was to calculate estimates of 1) heritability for ossification parameters of the cartilages in the front feet of the Finnhorse and 2) genetic correlations between the different ossification parameters. Estimates of heritability for different ossification parameters of the cartilages in the front feet and of genetic correlations between different parameters were evaluated in data consisting of dorsopalmar radiographs of the front feet and pedigree up to the fourth generation of 964 Finnhorses (age > or = 2 years; 345 females and 619 males). Ossification at the base of the cartilages and total ossification, including separate centres of ossification, were graded 0-5 according to the most proximal point of ossification and the presence of separate centres of ossification was recorded separately. The data were analysed using a model including a fixed sex-age subclass effect and a random animal effect. Variance and covariance components were estimated with the restricted maximum likelihood (REML) method assuming an animal model. Females had more ossification than males and this difference increased with age. The ossification in the medial cartilages progressed significantly with age in females but not in males. In the lateral cartilages, the increase in ossification with age was evident in both sexes. Separate centres of ossification were an incidental finding. Estimates of heritability for the ossification parameters varied slightly between the cartilages as well as between the front feet. For total ossification, the estimates of heritability varied between 0.31 (right lateral) and 0.50 (left medial) and were slightly higher for ossification at the base of the cartilages. High genetic correlations were found for total ossification between the medial and lateral cartilages in the foot and for parallel ossification parameters between the right and left foot. The estimates of heritability were relatively high, and both cartilages and front feet have a similar genetic tendency to ossify. This information is useful in further studies assessing other factors contributing to the ossification process and also in the planning and modifying breeding programmes.