Epidemiological and genetic study of exertional rhabdomyolysis in a Warmblood horse family in Switzerland.

This research paper investigates the prevalence and potential causes of exertional rhabdomyolysis, a muscle disorder resulting from severe exercise, in a family of Warmblood horses. The study revealed that horses with the glycogen synthase mutation (GYS1) had an increased risk of developing this condition, and that polysaccharide storage myopathy and genetic inheritance also played a factor in the family line.

Research Goals and Methods

• The research aimed to understand the symptoms, management and clinical signs of exertional rhabdomyolysis (ER) in Warmblood horses from a family with a high prevalence of the condition.
• The team also wanted to see if there was a correlation between ER, the presence of polysaccharide storage myopathy (PSSM), and the glycogen synthase (GYS1) mutation.
• The family under study consisted of a sire (male parent) with ER and 71 of his offspring.
• Information on episodes of ER, husbandry practices, feeding, and use were collected using a standardised questionnaire for the owners.
• All horses were also genetically tested for the GYS1 mutation, while 10 ER-affected horses underwent muscle histopathology evaluation.

Results and Findings

• ER signs were observed in 39% of the horses, and 51% of the entire family exhibited the GYS1 mutation.
• Horses with the GYS1 mutation were found to be 7.1 times more likely to develop ER compared to those without it.
• All muscle samples from ER-affected horses in the family displayed polysaccharide accumulation typical for PSSM.
• The study also suggested that the inclusion of fat or oil in the horse’s diet could improve the clinical signs of ER, but no other environmental factors seemed to have a significant effect on the ER symptoms.

Conclusions and Implications

• The research concluded that PSSM linked with the GYS1 mutation is a notable cause of ER in Warmblood horses.
• However, not all GYS1 positive horses manifest ER symptoms, pointing to other unknown causes of ER in this horse breed.
• The breeding of animals with the GYS1 mutation results in a high prevalence of ER due to the dominant mode of inheritance of this mutation.
• The findings of this research could be significant in devising strategic breeding and dietary plans to minimize the occurrence of ER in Warmblood horses.