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How long can EPM survive in hay or paddocks without opossums?

Updated on September 23, 2025

Pet's info: Farm Animal | Horse | Male | neutered | 24 years and 8 months old | 1500 lbs

How long can Sarcocystis neurona oocysts and sporocysts survive in the environment, say in a grass paddock or hay field? Could EPM contamination occur from baled hay or from turn out in paddocks where we haven't seen any opossums?

1 Answer

Most Helpful Answer

Angel Alvarado, LVT

Answered By Angel Alvarado, LVT

Licensed Veterinary Technician

Published on May 22, 2017

Some studies have suggested it can last as long as 1 year under perfect conditions. Extremes of temperature and ultraviolet radiation (sunlight) will destroy sporocysts. The oocysts are even more fragile.
In addition to possums, skunks and raccoons may act as hosts. Birds and insects can also serve as transport vectors however the organism requires an intermediate host to complete the life cycle. If these vectors transported infective sporocysts to the hay, it is possible to have contamination given the right conditions.
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