Management of Gut Worms in Horses

I’m a great advocate of managing animals – whether companions, working or farmed – in the most natural way possible, and this certainly goes for horses.

With increasing resistance to each of the main groups of wormers used to control gut worms in horses, owners and keepers are now being urged to review their current worming policies, which on many yards is simply ‘blanket’ treatment for all equines on a routine basis every few months.

For many years I’ve questioned the almost universal practice of routine interval dosing of horses.  This alone is a recipe for creating parasite resistance to the chemical wormers.  Neither of our horses has been wormed for the past 4½ years, since their quarantine worming when they came to live at Green Farm.  We knew that there hadn’t been horses here for over 20 years, so it was highly unlikely that there would be any equine-specific worm larvae in the pastures, so we devised a targeted, strategic approach, which in our case is effectively a ‘no-worm’ policy:

• On arrival, the horses were wormed and stabled for 24hours, then put into a quarantine paddock for 2 weeks
• At the end of the quarantine period, a Faecal Egg Count (FEC) was taken for each horse: the results were <50epg – no worm eggs seen, so horses were turned out onto the pastures
• One month later, a further FEC was taken, results again were <50epg, so we were fairly confident that the pastures were ‘clean’
• Droppings are collected on a daily basis – regular clearing of the pasture is probably the most important element in a reduced-dosing regimen, and even weekly collection of droppings can significantly reduce pasture contamination by worm larvae, and consequently horse worm burdens·
• Horses follow sheep onto the pastures (and sheep follow horses) – as worms are host-specific, the larvae of any horse worms are destroyed in the gut of sheep, and vice versa
• FECs are carried out 4 times per year (the result has always been <50epg) – if there was any change to this count, we would consider dosing, taking all other factors into account
• When horses travel to shows and have access to grazing that has carried other horses, they are tested within a week of returning home (this is adjusted if we have several outings closely together)
• Once a year horses are blood-tested to detect the presence of Tapeworm, which due to their lifecycle may not be detected in an FEC – although our vet has now advised that since our horses are so healthy, this isn’t necessary every year – only test if they lose condition
• In late summer, when bot flies are active, we keep a close look out for bot eggs, especially on the horses’ lower legs
• We also check under horse’s tails for signs of pinworm eggs
• And, finally, we give garlic granules in horses’ feeds throughout the year – not only is this reputed to discourage gut worms, but also the horse’s garlicky sweat is said to repel nuisance flies!

An element of caution is needed with regard to encysted redworm – in winter, worms may be present in an encysted (larval) stage of their lifecycle, meaning that there is no egg output despite the presence of the worm larvae.  In spring, the larvae hatch in large numbers and may cause colic-type symptoms.  Repeatedly low counts over a period of years make this less likely, but not impossible.

If you run your smallholding on organic principles, this management system should comply with the accreditation bodies’ requirements, and it’s wildlife friendly, as the horses’ dung won’t contain endectocides that harm dung beetles, earthworms and other invertebrates, which in turn are eaten by hedgehogs, badgers and foxes.

An additional incentive to adopting a targeted approach to worming is cost.  By carrying out a worm control programme as described, you can actually save money by reducing the amount of chemical wormers you administer to your horses.
This system is not going to suit all horses, or their owners, but it’s certainly worth looking at ways to reduce the use of wormers as routine worming can lead to the development of drug-resistant worms, and a major problem for all equines.

By the way, it does a FIT horse no harm to carry a small burden of worms – they develop a natural resilience to them, and there is some evidence that a low level of worms may actually be beneficial to horses.  An older horse, or one with compromised health may lose their acquired resilience, and consideration should also be given to foals, which have no acquired immunity to gut worms, so always follow your vet’s advice for individual horses on this subject.

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