What should I do if I think my horse has SPM/AM? - Owner Information
What is seasonal pasture myopathy?
- A toxic, highly fatal condition in pastured horses in the spring and fall that causes break down of postural muscles, breathing muscles, and heart muscle.
- It can affect one or several horses on the pasture and often resembles colic or founder.
- The condition resembles “atypical myoglobinuria/atypical myopathy” observed in northern Europe.
- In North America, it is caused by the ingestion of box elder tree seeds that contain the toxin hypoglycin A.
What are the signs?
Because signs can resemble severe colic or founder, a careful examination is necessary so as not to miss this diagnosis:
- Horses appear weak, stiff, may tremble and will lay down frequently or for long periods of time.
- If the heart and breathing muscles are affected, the gums become dark and horses will have difficulty breathing.
- Horses often have dark colored urine.
- The disease progresses quickly and most affected horses die within 24-72 hours after onset of signs.
Which horses are at risk?
o Horses exposed to box elder tree seeds
o Horses pastured for over 12 hours daily
o The fall season
o Horses that do not receive supplemental hay while they are out on pasture, including horses of normal or excess body condition
o Horses on sparse pasture with short grass
o Horses on pasture with many trees and dead wood on the ground
o Weeks when there has been heavy wind or rain
o Horses that are on a pasture for their first season, such as a young horse or a horse that has recently moved to a farm
- To see if your horse is at risk, please fill in our short risk assessment survey (click here).
When does it occur?
We investigated weather conditions in the Midwest for 14 previous cases of SPM.
- 13 cases occurred from September to November, and 1 case during a particularly wet, cool May (mean temperature, 54oF).
- 4 horses developed SPM 2 to 4 weeks prior to the first snowfall, 2 horses were evaluated 2 to 3 days after the first snowfall, and the remaining horses were evaluated 4 days to 6 weeks after the first snowfall.
What should I do if I think my horse has SPM?
- Call your veterinarian immediately if you think your horse is suffering from SPM or is otherwise unwell; the earlier the diagnosis is made, the better chance of saving your horse.
- Fill out our Risk Assessment Survey to determine your horses’ risk of SPM; we will respond within 24 hours Monday through Friday about the likelihood that your horse has SPM. Click here for the survey
- If your veterinarian believes your horse has seasonal pasture myopathy the best chance of saving your horse is hospitalization and intensive care.
- The University of Minnesota (612 625- 6700) and Iowa State University (515-294-1500) both provide intensive care 24 hours-a-day.
- If your veterinarian believes your horse may have SPM, please have them contact the University of Minnesota about screening for muscle damage, SPM, and box elder seed ingestion in a blood sample. A quick diagnosis of muscle damage can be made by your veterinarian from a urine sample that tests highly positive for hemoglobin/myoglobin on a urine stick.
- A blood sample submitted by your veterinarian can also detect muscle damage by showing very high serum creatine kinase (CK) activity.
- Confirm the diagnosis:
- If your horse is at moderate to high risk on the risk assessment survey and has evidence of muscle damage (high serum creatine kinase (CK), dark urine), we will ask that you or your veterinarian submit blood or urine samples to look for toxin ingestion and confirm the diagnosis.
- There will be no charge for the tests performed, (click here for how to submit samples).
- We will provide forms with a Billing Code in our email response to you so that you will not be charged to process samples.
- Confirmation of SPM can be made from fresh muscle biopsies (not fixed in formalin) sent to the University of Minnesota Neuromuscular Diagnostic Laboratory. (Click here for how to submit muscle biopsies).
2. Investigate pastures:
- If SPM is confirmed, we will ask you to answer a more detailed survey to identify risk factors, alternatives to pasture management, and possible preventative strategies.
If you are within our area, we may visit your farm and inspect the pastures to identify risk factors.
How can I help?
If you think you have or have had horses affected by SPM, please fill in the Risk Assessment Survey (click here).
You can help prevent future cases of SPM by taking simple measures to minimize your horses’ risk (click here).
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