ATYPICAL MYOPATHY (Atypical Myoglobinuria)
The Disease:
Atypical Myopathy is a frequently fatal condition affecting grazing horses in Autumn/Spring. Exactly what causes the diseases is currently unknown. Whatever causes the disease results in severe muscle damage which in turn can lead to respiratory failure and/or renal failure. All horses presenting with Atypical Myopathy suffer from severe generalised weakness - either difficulty getting up/can't get up or in worst case dead in the field. The most at risk horses are those aged less than 5 years or greater than 20 years who are kept at pasture and not receiving supplementary feed. Other factors that can increase the risk of a horse getting Atypical Myopathy are poor body condition, aged less than 18mths, kept in a field with a stream or pond in it, kept in a field with lots of dead leaves in it.
Clinical Signs:
- Stiff gait / reluctance to walk
- Mild colic symptoms
- Difficulty/Inability to stand
- Depressed but still want to eat if offered feed
- Muscle tremors
- Difficulty breathing
- Brown to black urine (please collect for vet if you see this)
Diagnosis:
Diagnosis in the field is based on clinical signs and taking a blood sample to check the muscle enzyme levels. The diagnosis can only be confirmed 100% by a muscle biopsy
Treatment:
If the horse can still walk move it immediately to the nearest stable/shelter as it will need intensive treatment/referral and this cannot be done adequately in the field. Clinical signs often progress rapidly and unfortunately there is about a 70-80% death rate despite supportive treatment. Move all other horses off the pasture and have them checked over by the vet when they arrive. Offer all other horses a small hard feed. There is no cure so treatment is purely supportive and will be recommended by your vet depending on the severity of the disease. Referral for intensive care is usually recommended (though can be very costly).
Prevention:
Limiting access to pastures during the high risk seasons is the best prevention. However, this is not always practical so if you do need to keep your horses at grass it is best to offer them a concentrate feed (hard feed) daily.
Please note that supplementing with hay during autumn actually increases the risk of Atypcial Myopathy when given on the ground in a humid environment (such as the warmer weather over Christmas) or if the hay contains mould.
