Types of worm

Roundworm – Large Redworm – Tapeworm – Lungworm Larvae – Giardia – Pin Worm – Encysted Small Redworm

Roundworm (ascarids)

Roundworms are large creamy white worms. They are not as common as redworm, and are more usually found in young horses. Infection can have serve consequences, with large worm burdens leading to intestinal blockages, poor growth and even death. Symptoms of infestation can include a pot belly appearance, poor coat condition and poor growth in youngsters.

Large Redworm (strongylus vulgaris)

Large redworm is far less common than the small redworm. In severe cases it can cause blockages in blood vessels, damaging organs and causing internal bleeding.

Large redworm can be detected in a worm count and will come under Strongyles on test results. This is because eggs from large redworm and small redworm have a very similar appearance therefore differentiation of the two is harder however, the treatment is the same.


The most common tapeworm in the UK, Anoplocephala perfoliata, is flat and can grow to about 8 cm long by 1.5 cm wide. The body consists of numerous segments (proglottids) and the head (scolex) has four suckers (bothridia) which the tapeworm uses to attach itself to the gut wall. They mainly reside at the ileo-caecal junction and adjacent areas of the intestine and caecum. Infected horses pass tapeworm eggs onto the pasture where they are consumed by the intermediate host, free-living oribatid mites. The eggs develop into larvae within the mite. When the mite is ingested by a grazing horse, the larvae are released within the horse where they develop into adult tapeworms capable of completing the cycle by releasing eggs. The proglottids mature into a sac of eggs (gravid proglottids) which breaks up, releasing the eggs whereupon the cycle begins again.

Due to the tapeworm’s egg release mechanism, burdens cannot be reliably detected by faecal egg counts (FEC). Although tapeworm eggs can sometimes be detected in FECs, the true tapeworm burden can be substantially underestimated as eggs can only be counted if the segments break up and release the eggs uniformly within the faeces.

We recommend that horses are tested every 6 – 12 months depending on individual risk factor, alongside regular faecal testing.

Lungworm Larvae (dictyocaulus arnfieldi)

Lungworm is a lung parasite. The larvae burrow through the intestine walls once eaten by the horse or donkey, travelling through the body to the lungs where they develop into adult lungworm. It can take around 6 weeks to reach maturity. Infection of lungworm irritate the lungs, causing coughing, breathing difficulties and can cause bronchitis.

Lung worm can be trickier to detect in horses as they may be infected but the parasite may not reach adult egg laying stages. Due to this we test three samples, taken over a three day period using the Baermann technique and sedimentation.

Testing should be carried out if your equine is coughing, wheezing or has a mucus discharge and you suspect lungworm. For donkey’s lungworm egg counts should be tested routinely as part of your worming programme.

If grazing your horses / ponies alongside donkeys then it is advised that you carry out a faecal egg count for your donkeys, who are assumed to be the natural host of the parasite (as well as your horses if lung worm is suspected). Lungworm larvae can live on pasture a long time, therefore good pasture management can help reduce infection for the equine (and donkeys). Donkeys and equines can live together quite safely, provided that you adopt a good de-worming programme with your vet.

Donkeys, which usually show few signs of the infection, are the prime source of pasture contamination for horses.

Giardia (giardiasis)

Giardia is less talked about in horses however can be the cause of intermittent diarrhoea. Giardia is a cyst and is more commonly found in younger equines/ foals. Giardia infects the small intestine and can be spread through pasture. It is also a zoonotic as it can be passed from animal to humans. If your horse has unexplained diarrhoea then a giardia test would be beneficial. Giardia is an emerging problem is dogs but can be found in companion animals and ruminants. We offer an Antigen Rapid test kit for Giardia.

Pin Worm

Pinworm are not a true intestinal parasitic worm but can be highly irritating to horses! Horses ingest pinworm eggs which then travel to the intestine where they hatch and live. Instead of being passed out in droppings, Pinworm make their escape and lay eggs around the anus. It is then common to see horses itching their tails/ bum on anything that may relieve the itch!

As eggs are not passed in the horses faeces, it is unlikely a worm count will show pinworm eggs. For a more accurate result we use a sticky tape impression which is taken from around the hairless area of the horses anus and then viewed under a microscope.

Encysted Small Redworm

Small redworm larvae can encyst within a horse’s gut wall throughout the year. This can lead to the damaging of the gut, which can cause diarrhoea and colic. Please note this does not show up on a worm count test so please speak to your vet.

Available test kits for Equine

You can now purchase your freepost Animal specific worm egg count from our website. You will receive your results within 48 hours of receipt by email or post whichever you prefer. Our staff are fully qualified Amtra SQP’s able to advice on Anthelmintic products.

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