Q: We have half a dozen horses and we pick up all their manure promptly to minimise the parasite problem. They are on a regular worming regime. We buy in all our hay and I was wondering whether any particular parasites can be introduced to horses through hay?
Jim, Michigan, US
A: Hi Jim. Your strategy against parasites has been shown to work well, when carried out thoroughly and consistently. By effectively removing the feces, you break the life cycle of the worms and minimize the infection pressure. This should enable you to reduce your costs for dewormings considerably.
I often get questions about the risks of parasites hiding in hay and silage. We cannot expect strongyle larvae to survive the dry and warm conditions in the hay. They prefer cold and moist conditions. Hay is typically stored for at least six months before it is fed to the horses, and it should be long enough to kill the strongyles.
The eggs of the roundworm Parascaris equorum are very environmentally resistant and are reported to survive for years on pasture.
It is therefore theoretically possible that eggs can be found in the hay, but it would most likely be very small amounts. Tapeworm eggs are ingested by certain mites that live on the pasture. It remains unknown whether these mites can survive in the hay.
Taken together, there are some theoretical possibilities that parasite burdens can be acquired from hay, but it is unlikely to be of any significance.