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Posted on Mar 5, 2019 in Articles, Health & nutrition, Veterinary

Two Rivers Veterinary Practice tell us about targeted worm control for horses -Part 1

Two Rivers Veterinary Practice tell us about targeted worm control for horses -Part 1


Horse worms are becoming resistant to some commonly used de­wormers. For this reason it is no longer advisable to interval treat our horses. Instead, targeted deworming, using faecal egg count monitoring, is recommended. The aim of this approach is not to eliminate all worms from the horse but rather to prevent clinical disease.

horse with worms

Worms can cause a variety of clinical sigs including poor condition and weight loss, colic, diarrhoea and colitis, respiratory signs, and perineal skin/tail rubbing (pinworm).

Faecal worm egg counts (FWEC’s) should be started in the Spring and repeated every 2­3 months throughout the grazing season. Fresh (warm) samples should be collected into an airtight container, kept cool and delivered to the surgery that day. Ideally take a small sample from 4 or 5 faecal balls instead of just one but we only need 3g of faeces in total.


FWEC’s will identify those horses that are carrying significant adult worm burdens. Those with counts of greater than 200eggs per gram should be targeted for treatment. Horses with very high burdens can be sampled after de­worming to ensure the dose has worked and no drug resistance is present. FWEC’s do have limitations. They will not detect the following types of worms:

* Tapeworm – treat for tapeworm once (Autumn) or twice (Spring and Autumn) annually based on ELISA testing for tapeworm antibody on blood or saliva. This test only has to be done once on a proportion of horses on the yard as a guide to treatment.

equine tapeworm

* Larvae – only adults lay the eggs which are detected by egg counts. For this reason, all horses should receive larvicidal treatment for encysted redworm ideally in the Winter after a hard frost. Only a five day course of fenbendazole (Panacur) or Moxidectin (Equest) are effective against these stages. With resistance to fenbendazole increasing, moxidectin is usually the drug of choice but it should be avoided in foals, very thin and miniature horses.

* Pinworm – detected by sellotape smears of the perianal skin ­ and Bots.


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