Your horse did not inherit MYHM and is considered normal. They cannot pass the mutation on to offspring.

• Stiffness.
• Extreme muscle pain.
• Weakness.
• Muscle tremors.
• Lethargy.
• Muscle swelling.
• Rapid heartbeat and breathing.
• Loss of appetite.
• Difficulty getting up when laying down.
• Dark urine.
• Rapid muscle loss – 40% loss within a 48hr period.

• Vaccinations - Specifically, influenza, rhinovirus, and strangles or other vaccinations that cause muscle inflammation.
• Upper respiratory infections such as strangles.
• Pigeon Fever exposure.
• Muscle damage.

• Quality high protein diets are recommended with amino acids supplemented as needed. Additional protein may be supplemented after an episode to support muscle growth.
• Avoid any form of strangles vaccine.
• Use intranasal vaccines when possible.
• Only use intramuscular vaccines when necessary.
• Spacing individual vaccines out 4-6 weeks is recommended.(Strangles, Rhinovirus, Influenza vaccines are NOT recommended)
• Take care to quarantine any new horses for 14 days to avoid introducing an infectious agent to your barn.
• Responsible breeding can reduce the number of affected horses.

Immune-mediated myositis (IMM) is one of the forms of MYHM. If IMM is triggered, contact your veterinarian immediately and begin steroid therapy. Improvement in appetite should occur within 48 hours of steroid therapy. Muscle atrophy should stop, and muscle mass should return within 2-3 months. Though, some muscles may have a permanent indentation. Without steroids, muscles atrophy will still eventually stop, but the return of muscle mass may take a longer period of time. IMM usually resolves without long term consequences in horses with one copy of MYHM. Homozygous horses are likely to develop more severe atrophy and are less likely to recover.

Horses recovering from IMM should be fed a concentrate with high-quality protein balanced for vitamins and minerals. Alfalfa hay and amino acid supplements may provide building blocks for muscle developments.

For horses with nonexertional rhabdomyolysis, treatment often consists of flushing infected guttural pouches and giving antibiotics. Corticosteroids may be prescribed. Treatment with dantrolene may be administered. Nonexertional rhabdomyolysis is more rare than IMM, but often more severe.

When breeding any horse, probability of offspring inheriting genetic mutations should always be a factor to consider.

Expected breeding outcomes are shown below. A normal MYHM gene is indicated by "N". A mutated MYHM gene is indicated by "My".

100% chance of a foal who does not carry a copy of MYHM and is considered normal. They cannot pass on the mutation to offspring themselves.

50% chance of a foal who does not carry a copy and is considered normal. They cannot pass on the mutation to offspring themselves.

50% chance of a foal who inherits one copy and likely to experience mild/moderate symptoms with severe symptoms possible. This horse can pass MYHM on to offspring.

100% chance of a foal who inherits one copy and is likely to experience mild/moderate symptoms with severe symptoms possible. This horse can pass MYHM on to offspring.

• VGL-MYHM
• UCDAVIS-MYHM
• MSU-MYHM
• CORNELL-MYHM

Your horse inherited one copy of MYHM and may be affected by the disease. They may experience symptoms but will likely be more mild than that of homozygous (My/My) horses. Your horse may experience rapid muscle atrophy from IMM, but generally will recover muscle loss without long term effects. Your horse can pass on the mutation to offspring and care should be taken when breeding to reduce the chance of producing an affected horse.

• Stiffness.
• Extreme muscle pain.
• Weakness.
• Muscle tremors.
• Lethargy.
• Muscle swelling.
• Rapid heartbeat and breathing.
• Loss of appetite.
• Difficulty getting up when laying down.
• Dark urine.
• Rapid muscle loss – 40% loss within a 48hr period.

• Vaccinations - Specifically, influenza, rhinovirus, and strangles or other vaccinations that cause muscle inflammation.
• Upper respiratory infections such as strangles.
• Pigeon Fever exposure.
• Muscle damage.

• Quality high protein diets are recommended with amino acids supplemented as needed. Additional protein may be supplemented after an episode to support muscle growth.
• Avoid any form of strangles vaccine.
• Use intranasal vaccines when possible.
• Only use intramuscular vaccines when necessary.
• Spacing individual vaccines out 4-6 weeks is recommended.(Strangles, Rhinovirus, Influenza vaccines are NOT recommended)
• Take care to quarantine any new horses for 14 days to avoid introducing an infectious agent to your barn.
• Responsible breeding can reduce the number of affected horses.

Immune-mediated myositis (IMM) is one of the forms of MYHM. If IMM is triggered, contact your veterinarian immediately and begin steroid therapy. Improvement in appetite should occur within 48 hours of steroid therapy. Muscle atrophy should stop, and muscle mass should return within 2-3 months. Though, some muscles may have a permanent indentation. Without steroids, muscles atrophy will still eventually stop, but the return of muscle mass may take a longer period of time. IMM usually resolves without long term consequences in horses with one copy of MYHM. Homozygous horses are likely to develop more severe atrophy and are less likely to recover.

Horses recovering from IMM should be fed a concentrate with high-quality protein balanced for vitamins and minerals. Alfalfa hay and amino acid supplements may provide building blocks for muscle developments.

For horses with nonexertional rhabdomyolysis, treatment often consists of flushing infected guttural pouches and giving antibiotics. Corticosteroids may be prescribed. Treatment with dantrolene may be administered. Nonexertional rhabdomyolysis is more rare than IMM, but often more severe.

When breeding any horse, probability of offspring inheriting genetic mutations should always be a factor to consider.

Expected breeding outcomes are shown below. A normal MYHM gene is indicated by "N". A mutated MYHM gene is indicated by "My".

50% chance of a foal who does not carry a copy and is considered normal. They cannot pass on the mutation to offspring themselves.

50% chance of a foal who inherits one copy and likely to experience mild/moderate symptoms with severe symptoms possible. This horse can pass MYHM on to offspring.

25% chance of a foal who does not carry a copy and is considered normal. They cannot pass on the mutation to offspring themselves.

50% chance of a foal who inherits one copy and likely to experience mild/moderate symptoms with severe symptoms possible. This horse can pass MYHM on to offspring.

25% chance of a foal who inherits two copies and will likely experience severe symptoms when exposed to a trigger. This horse will pass MYHM on to offspring 100% of the time regardless of the other parent’s MYHM status.

50% chance of a foal who inherits one copy and likely to experience mild/moderate symptoms with severe symptoms possible. This horse can pass MYHM on to offspring.

50% chance of a foal who inherits two copies and will likely experience severe symptoms when exposed to a trigger. This horse will pass MYHM on to offspring 100% of the time regardless of the other parent’s MYHM status.

• VGL-MYHM
• UCDAVIS-MYHM
• MSU-MYHM
• CORNELL-MYHM

Your horse inherited two copies of MYHM and is homozygous for the defect. Your horse will likely experience severe symptoms if/when triggered. If your horse experiences rapid muscle loss from IMM it will be more severe than a N/My horse and is less likely to recover from the muscle loss. Your horse will pass on MYHM to their offspring regardless of the other parent's MYHM status.

• Stiffness.
• Extreme muscle pain.
• Weakness.
• Muscle tremors.
• Lethargy.
• Muscle swelling.
• Rapid heartbeat and breathing.
• Loss of appetite.
• Difficulty getting up when laying down.
• Dark urine.
• Rapid muscle loss – 40% loss within a 48hr period.

• Vaccinations - Specifically, influenza, rhinovirus, and strangles or other vaccinations that cause muscle inflammation.
• Upper respiratory infections such as strangles.
• Pigeon Fever exposure.
• Muscle damage.

• Quality high protein diets are recommended with amino acids supplemented as needed. Additional protein may be supplemented after an episode to support muscle growth.
• Avoid any form of strangles vaccine.
• Use intranasal vaccines when possible.
• Only use intramuscular vaccines when necessary.
• Spacing individual vaccines out 4-6 weeks is recommended.(Strangles, Rhinovirus, Influenza vaccines are NOT recommended)
• Take care to quarantine any new horses for 14 days to avoid introducing an infectious agent to your barn.
• Responsible breeding can reduce the number of affected horses.

Immune-mediated myositis (IMM) is one of the forms of MYHM. If IMM is triggered, contact your veterinarian immediately and begin steroid therapy. Improvement in appetite should occur within 48 hours of steroid therapy. Muscle atrophy should stop, and muscle mass should return within 2-3 months. Though, some muscles may have a permanent indentation. Without steroids, muscles atrophy will still eventually stop, but the return of muscle mass may take a longer period of time. IMM usually resolves without long term consequences in horses with one copy of MYHM. Homozygous horses are likely to develop more severe atrophy and are less likely to recover.

Horses recovering from IMM should be fed a concentrate with high-quality protein balanced for vitamins and minerals. Alfalfa hay and amino acid supplements may provide building blocks for muscle developments.

For horses with nonexertional rhabdomyolysis, treatment often consists of flushing infected guttural pouches and giving antibiotics. Corticosteroids may be prescribed. Treatment with dantrolene may be administered. Nonexertional rhabdomyolysis is more rare than IMM, but often more severe.

When breeding any horse, probability of offspring inheriting genetic mutations should always be considered. Responsible breeding is key with MYHM due to extremely poor prognosis for horses who experience an episode.

Expected breeding outcomes are shown below. A normal MYHM gene is indicated by "N". A mutated MYHM gene is indicated by "My".

100% chance of a foal who inherits one copy and is likely to experience mild/moderate symptoms with severe symptoms possible. This horse can pass MYHM on to offspring.

50% chance of a foal who inherits one copy and likely to experience mild/moderate symptoms with severe symptoms possible. This horse can pass MYHM on to offspring.

50% chance of a foal who inherits two copies and will likely experience severe symptoms when exposed to a trigger. This horse will pass MYHM on to offspring 100% of the time regardless of the other parent’s MYHM status.

100% chance of a foal who inherits two copies and will likely experience severe symptoms when exposed to a trigger. This horse will pass MYHM on to offspring 100% of the time regardless of the other parent's MYHM status.

• VGL-MYHM
• UCDAVIS-MYHM
• MSU-MYHM
• CORNELL-MYHM