Estimation of heritability of laryngeal Hemiplegia in the Thoroughbred horse by gibbs sampling

Laryngeal Hemiplegia (LH) leads to a reduction in performance and because of it many promising racehorses have been forced to end their racing career. Therefore it is important for breeding good racehorses to estimate the heritability of LH. In this study, the computer program was developed based on the Bayesian analysis with Gibbs sampling for estimating the heritability of categorical traits assuming liability. A total of 706 records with LH-grade in Thoroughbreds aged 2 to 5 years were assigned for the genetic analysis. LH-grades consisted of five severity classes from 0 to 4. Racehorse breeders are often interested in whether the genetic effect controlling a complex disorder is present in the population. To answer this question, the binary trait analysis would be also useful. The heritability of LH-grade in the Thoroughbred horse was then also estimated as a binary or as a categorical trait. The mode values of the posterior distributions of heritability were 0.23 and 0.20 for the binary and the categorical trait, respectively. The fact that in the Thoroughbred population studied LH is at least partially controlled by genetic factors leads to the suggestion that when applying adequate breeding measures the prevalence of LH will be able to be reduced.