Management of Gut Worms in Horses

By Carole Youngs

(not an expert, but passionate about horse welfare)

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’
  • poo_pickingDroppings 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.

horses_grazingIf 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.

A slightly shorter version of this article was first published in September Diary 2010

Review by Dr Martin K. Nielsen

Assistant professor in equine parasitology at the Maxwell H. Gluck Equine Research Center
University of Kentucky

I was just made aware of your article on the smallholderseries website, and I have to congratulate you for a fantastic job! Not only have you understood all the current concepts of modern parasite control correctly. You simply take all the important issues into account, and you avoid ignoring important aspects, as is often done. You have also been able to translate your knowledge into an actual program for your horses, which I find remarkable. I particularly admire how you continuously monitor the parasite loads in your horses. I find this very important, no matter how the parasite control program is designed. And last but not least, you have written up a great description of your approach. Your parasite control program simply serves as a great example of how it can be carried out.

You questions about the potential positive effects of parasite burdens are very interesting. There are lots of indications from humans and other animal species that parasite burdens can modulate the immune response and reduce inflammation. In humans, porcine Whipworms are now used for treating Inflammatory Bowel Syndrome (Crohn’s Disease) -  and it helps!!

Article by Martin K. Nielsen
An evidence-based approach to equine parasite control: It ain't the 60s anymore