What are worms?

Worms are internal parasites (which live within, and take nourishment from their host-in this case the horse). Intestinal worms can seriously damage your horse and in some instances can be fatal. Implementation of an effective de-worming programme is the best form of prevention. 

The most common worms are: 

Small Redworms (Cyathostomins)

Small Redworms: During cold spells their larval stage burrows into the gut wall and ‘encysts’ before re-emerging in the spring. Large emergence can cause serious damage to the gut wall causing Small Redworm disease (Cyathostominosis)which can be fatal in up to 50% of cases. 

Large redworms (Large Strongyles) 

Large Redworms: The adult stage eats away at the gut wall causing damage. The larval stage migrates into the bloodstream, moving around organs causing significant damage. This can also cause damage to arteries, causing blood clots and even weakening which can be fatal.

Large Roundworms (Ascarids) 

Ascarids: These are normally seen in young stock and cause damage to the liver and lungs. In high numbers they can cause blockages causing the gut to rupture. 


Tapeworm: Tapeworm causes much less damage to the gut wall than other worms but they like to gather in high numbers at a site between ileum and caecum (illeocaecal junction). This can cause a blockage leading to colic. 


Bots:  Bot flies are highly irritant to horses and lay eggs on the horses’ hair. Whilst grooming the horse can ingest these eggs and the larvae end up growing on the lining of the stomach. Large volumes can cause stomach blockages however normally these larvae cause no clinical signs.

It’s clear preventative measures are better than cure and a strict worming management programme including targeting certain worms at optimum times of the year is recommended. 

How do you know if your horse has worms? 

Even a horse that appears to be in good health may have worms causing internal damage, particularly in young and aged horses .A worm burden can result in: 

  • Weight loss
  • Diarrhoea
  • Colic
  • Loss of appetite
  • Dull, starring coat
  • Severe infection can kill

Faecal Egg Counts (FEC) can be carried out on faecal samples at our clinic to check the eggs which are being shed. This is a useful indicator of how high your horses worm burden is at that time. 

How do horses get worms? 

Your horse will catch worms if it is turned out with other horses or donkeys that have worms, because the pasture will be contaminated with eggs and larvae. Your horse will eat these asit grazes. Pastures can remain contaminated for a considerable time.Hence we advise regular removal of faecal material from pastures and good land management to minimise the burden on your pastures.

Worming your horse: 

There are two methods of worming your horse: 

  • ROUTINE worming means you administer an anti parasite medication (a wormer) to your horse throughout the year, at the interval described by the wormer you have chosen.(NO LONGER RECOMMENDED). 
  • STRATEGIC worming means you only worm your horse if a faecal, saliva or blood sample suggests that the horse has a high worm burden.

Foal worming: Foals are to be wormed differently to adult horses and are very susceptible to worms which can cause death. Alongside passive immunity from worming your mare in her last trimester a strict worming protocol should be followed starting from 6 weeks old. Please give the clinic a call for a tailored worming plan. 

Strategic worming: This is most commonly used today as it will reduce resistance found in common drug groups. Saliva tests and blood samples can be taken to check for tapeworm burden. In 2019 a blood test was created to test for Encysted Redworm. These are best used during optimum times where the risk is highest. Faecal egg counts are a very popular during grazing season (spring –autumn) and are used to count the Strongyle burden of your horse. The benefits of these are if your horse is negative, worming is not needed at that time and we can also monitor for any resistance problems on a pasture. 


  • Use correct dose of wormer for weight of horse/ pony-Collect a weight tape from us or use our weigh bridge here at Abbey Equine.
  • New arrivals to the yard-should be wormed for all parasites on arrival and kept in isolation.(Ideally this should be for 2 weeks for other infectious diseases such as Strangles, Ringworm, Herpes Virus and Equine Influenza).
  • Poo pick paddocks regularly to decrease pasture egg burden.
  • Paddock Rotation –resting the paddock for at least 3 months if possible, or grazing with sheep or cattle (as horse wormsare unable to survive in these animals).
  • Have a worming programme that everyone sticks to on a livery yard. Get all owners to worm their horses on the same day with the same product.


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If you have any veterinary or administrative enquiries you can phone on 01873 840069 during business hours (Mon-Fri 9.00am – 5.30pm) or alternatively complete the form below and submit your enquiry. One of our veterinary, nursing or administrative staff will be pleased to respond to you by phone or email as soon as possible during office hours.

24hr Emergency No: 01873 840 069

Abbey Equine Clinic

Llansabbath Barns, Llanellen, Abergavenny, Gwent NP7 9BY
T: 01873 840 069
E: office@abbeyequine.co.uk

Abbey Equine Chepstow
Ride and Stride, St Arvans, Chepstow. NP16 6DN
T: 01291 444877
E: office@abbeyequine.co.uk

Opening Hours: Monday – Friday: 9:00am – 5:30pm
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Abergavenny Branch

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