Heritability of recurrent exertional rhabdomyolysis in Thoroughbred racehorses.

This research aimed to determine the likely mode of inheritance for recurrent exertional rhabdomyolysis (RER), a muscle disorder, in Thoroughbred racehorses and identify potential original carrier horses. The study found that RER is likely passed through an autosomal dominant gene with variable expression, and all affected horses in the study shared a common ancestor.

Research Methods

• The researchers selected four families of Thoroughbred racehorses, each containing 3 to 53 horses, which exhibited a high prevalence of RER for their study.
• They also selected 62 Thoroughbred horses diagnosed with RER and 34 control Thoroughbred racehorses without RER to identify probable original carrier horses for RER.
• The diagnosis of RER was confirmed by a veterinarian and verified by detecting high serum creatine kinase activity, an indicator of muscle damage.
• The researchers collected and entered into a database the pedigree information of all the horses dating from 1930.
• The pedigrees of horses in the four selected families were visually inspected for a pattern of inheritance. They were also used for calculating the contributions of original carrier horses and inbreeding coefficients.
• The Markov chain Monte Carlo technique, a method used for making precise estimates, was used to analyze the pedigrees of the affected and control horses for the conditional probability of original carrier genotypes.
• A dominant mode of inheritance with variable expressivity model was used for the study.

Research Findings

• Based on the pedigree analysis of the four families, the researchers concluded that RER is likely inherited through an autosomal dominant gene with variable expression.
• It was discovered that all affected horses from the four families shared a common ancestor.
• This ancestor and five other stallions were found to have a conditional probability of 1.00 for being affected with RER, indicating they are very likely to be original carriers.
• These six stallions were found to share a common male ancestor within 3 to 5 generations.

Conclusions

• From this study, it can be inferred that the RER trait has been present in Thoroughbred racehorses for over 70 years.
• RER is likely inherited as an autosomal dominant trait with variable expression.