Worm Egg Counts in horses – are they worth it?
None of us want our horses to be carrying a heavy worm burden. Unfortunately, the heavy use of wormers over the years has led to a significant amount of worm resistance within the equine population. This means that some of the wormers are potentially no longer effective at eliminating worm burdens in some of the horses. So, alternative means of managing worms have had to be found.
Problems with resistance can be overcome by monitoring faecal worm egg counts (FWEC) of all horses at regular intervals. This can ensure only those individual horses with a significant worm burden are treated using the appropriate wormers at the appropriate times.
There is an increasing risk of resistance to anthelmintics (wormers), so we must use different strategies to protect our horses.
How do horses get worms?
Worms naturally occur in horses and are present in most horses at varying levels of infestation.
How the horse gets infected by worms will differ from worm to worm depending on the lifecycle, but generally, eggs are ingested from infected pasture and then develop inside the intestinal tract (or, in some cases, the horses’ lungs) where they can cause disease.
These eggs produced by the adult worm will then be shed in the faeces to increase existing worm burdens on the pasture and to potentially infect new horses.
When the worms are present in low numbers, worms cause minimal problems. However, if they are present in larger numbers, they can severely affect the horses’ health and can result in poor body condition, colic, and general ill-health.
What worms can affect horses?
Large Redworms (Strongylus vulgaris):
The “large strongyles” or “large redworms” are potentially the most dangerous but are less common nowadays due to the widespread use of wormers. The adults feed on the gut wall which can result in extensive damage and bleeding and can block arteries leading to the gut, leading to gut death and severe surgical colic.
These worms live in the large intestine of horses and donkeys. There are various species and the developing larvae migrate around the body. How long it takes to migrate through the body depends upon the species. This may be as little as 7 months or 12 months. Eventually, they find their way back to the lumen (the inside) of the intestine.
Small redworms (cyathostomins)
The “small redworms” are also known as cyathostomins. These worms are very common in horses. They go through a dormant phase, where they burrow into the gut wall, become encysted (dormant), and then emerge in spring.
