Treatment of Muscle Disease in Horses

Treatment of Muscle Disease (Tying Up / Exertional Rhabdomyolysis)

Key Concepts

Re-evaluation of Training:
Gradually re-evaluate the horse’s training program by initially slowing down workouts and reducing current exercise levels to prevent exacerbation of symptoms. A systematic approach to retraining is essential, which includes monitoring the horse's response to reduced activity.
Nutritional Management:
Maintain a diet with a Calcium to Phosphorus (Ca:P) ratio of 2:1, as an imbalance can lead to muscle and bone issues.
Ensure the provision of high-quality hay, ideally tested for nutritional composition to ensure it meets the horse’s needs.
Supplement with an additional 30-50g of Sodium Chloride (NaCl) and 15-25g of Potassium Chloride (K-Cl) daily to support electrolyte balance, especially during hot weather or heavy exercise.
Avoid concentrates or grains that contain more than 15-20% Non-Structural Carbohydrates (NSC) as high NSC levels can trigger episodes of tying up.
Provide a balanced fat content in their diet of 4-8% to help mitigate muscle energy demands.
Medications for Severe Cases:
Administer Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) for a duration of 3-6 days with careful consideration of kidney health due to potential side effects on renal function.
Consider Acepromazine for tranquilization purposes, which helps promote healing through vasodilation and enhances blood flow to affected muscle tissues.
If symptoms of myoglobinuria are present, Intravenous Fluid Therapy (IVFT) with isotonic fluids is crucial to support kidney function and ensure the excretion of myoglobin.
Muscle relaxants such as methocarbamol or dantrolene can be beneficial in alleviating muscle spasms.
Antioxidants such as Vitamins E, B, and C should be included to reduce oxidative stress on the muscles.
Identifying Stressors:
In cases of recurrent muscle issues, it is vital to identify potential stressors that could be contributing to the condition, such as the presence of other horses that may induce anxiety or competition. Factors like changes in environment, feeding practices, or training schedules should also be reviewed.

Specific Conditions

PSSM-1 (Polysaccharide Storage Myopathy):
Implement a diet low in starch and sugar, ideally less than 12%, while maintaining protein levels around 20% to support muscle health.
Limit or avoid high-sugar feeds such as sweet feed, corn, wheat, oats, barley, and molasses to minimize the risk of glycogen excess in muscles.
Supplement the diet with vegetable oil to increase caloric intake while remaining within safe carbohydrate limits.
Ensure consistent exercise to promote muscle adaptation while avoiding long periods of inactivity that could lead to muscle stiffness.
Hypp (Hyperkalemic Periodic Paralysis):
Strictly limit the horse’s potassium intake to less than 1% while regularly testing hay for potassium content (aiming for 1-2%) to maintain safe levels.
Avoid feeding alfalfa and clover hay, known to be high in potassium, which can trigger muscle episodes.
Use plain oats cautiously, considering their starch content, while ensuring an overall balanced diet.
Maintain a consistent exercise regimen to help stabilize muscle function and manage condition flare-ups.
Myofibrillar Myopathy:
Follow a diet comprising moderate starch/sugar levels (less than 15%), protein (around 15%), and fat (4-8%).
Include antioxidants like Vitamin E and Coenzyme Q to support muscle recovery and metabolic health.
Consistent exercise is paramount; it is particularly important for Warmblood breeds known to be more susceptible.
Implement a long warm-up routine that involves stretching to prepare muscles for activity, and limit maximum training sessions to 30-50 minutes, following a regimen of 3 days of work and 2 days of rest.
Atypical Myopathy:
Limit exposure to pigmented nephropathy which can exacerbate symptoms; IV-fluids may be necessary to support hydration.
Ensure glucose availability and prevent excessive gluconeogenesis; Karo syrup can be utilized as it provides rapid glucose supply.
Continually monitor cardiac function as it can be affected by metabolic status, and provide deep bedding to ensure comfort for affected horses.
IMM (Immune-Mediated Myopathy):
Administer IV fluids if muscle enzyme levels are elevated to promote hydration and eliminate toxins.
Use Dexamethasone and prednisolone for their anti-inflammatory properties while adhering to a proper tapering schedule to prevent adverse effects from abrupt cessation.
Myonecrosis:
Drain abscesses as necessary and prescribe broad-spectrum antibiotics (e.g., high-dose penicillin, metronidazole) to combat infection alongside careful monitoring of the horse's overall health.

General Treatment Guidelines

Acute/Severe Rhabdomyolysis:
Closely monitor plasma creatinine and ensure adequate water intake while administering NSAIDs to mitigate pain and inflammation.
Implement pain relief through the use of additional medications aimed at maintaining comfort. Acepromazine can be particularly effective for promoting vasodilation.
After a period of 48 hours of rest, initiate a gradual exercise program tailored specifically to the horse’s condition while carefully observing for signs of relapse.

Learning Objectives

Formulate Treatment Plans specifically tailored for horses suffering from muscle diseases, which consider both pharmacological and non-pharmacological strategies.
Provide Advice on Prevention to horse owners regarding lifestyle modifications and nutritional strategies to mitigate the risk of muscle disease.
Understand Common Treatments based on the underlying pathophysiology of various muscle diseases, enhancing therapeutic efficacy.
Recognize Importance of Dietary Management informed by the specific requirements of different muscle diseases and the importance of maintaining a balanced diet.
Establish Proper Exercise Programs tailored specifically for horses impacted by muscle disease to promote recovery and limit the risk of recurrence.