Estimation of heritability and genetic correlation for behavioural responses by Gibbs sampling in the Thoroughbred racehorse.

This research investigates the genetic factors influencing the behaviour of Thoroughbred racehorses during medical examinations. The study concludes that genetic variations have a significant impact on the horses’ responses, with a notable consistency in behaviour across different types of veterinary evaluations.

Research Method

• The study focuses on behaviour during three types of tests – i.e. examination of the conjunctiva (eye tissue), heartbeat monitoring (auscultation), and blood sampling – that were conducted at a horse training centre in Japan between 1993 and 1995.
• The researchers used Bayesian analysis accompanied by Gibbs sampling. This statistical method enables researchers to make probabilistic statements about unknown quantities by generating an estimate based on prior data and current observation.
• Behavioural responses were ranked in four categories, which were treated as both categorical and binary measures. This ensured robustness of the findings by comparing outcomes across different statistical models.

Findings

• The heritability estimates (indicative of genetic influence) ranged from 0.23 to 0.28. This suggests that a horse’s genetic makeup significantly contributes to its responses during medical procedures.
• There also appeared to be strong genetic correlation (approximately 0.9) among different behavioural responses. This indicates that these behaviours are likely influenced by the same genetic trait.
• In order to validate this high correlation, a repeatability threshold model was employed. This model assumes that the behavioural responses represent three manifestations of the same genetically identical trait.
• The resulting heritability estimate was 0.23 – consistent with the findings above – whereas repeatability rates were extremely high (0.97-0.98). The researchers interpret this as reflecting a strong influence of individual temperament on a horse’s behaviour.

Implications

• The results underscore the value of genetic considerations in horse breeding. Recognising the strong influence of heritable traits, as viewed through their responses during medical procedures, provides crucial insights for breeders and trainers.
• The high correlations and repeatability rates also suggest that mapping an individual horse’s temperament could enable better management of its behaviour during different types of medical tests.