Worming your new horse

By Wendy Talbot on 25 September 2020

Few things are more exciting than the arrival of a new horse. For the first time owner it’s a dream come true and for experienced owners it’s thrilling to continue to fuel your addiction! While it’s fun to make arrangements for stabling and turnout, tack and feeding, it’s also very important to make provision for your new horse’s health and this includes worming. The best place to start is to have a chat with your vet or RAMA to make advance plans for your new horse’s worm control programme before he arrives.

Reduce the risks

A new horse can bring any number of infections into the yard – including worms. It’s up to you as his owner to reduce the potential risks, not only to him but also to the other horses on the premises. A new horse could bring the unwelcome addition of high levels of worms, with the extra problem that these may be worms that are resistant to some of the worming treatments currently available. This means they may be tougher to get rid of and they could cause ongoing problems for the entire yard.

Err on the side of caution

Unless you have a very clear and trustworthy worming history for your new horse, it is always best to err on the side of caution and give a dose of wormer on arrival that treats for encysted small redworm, roundworms, tapeworm and bots. Remember to weigh your new horse before worming so that you can give an accurate dose. If you have a new foal or youngster you should speak to your vet or RAMA as youngstock usually need to be treated differently.

Dosing now will ensure that your new horse does not have a large worm burden (it is not realistic to expect them to be completely worm free) and reduces the risk of bringing resistant worms onto the yard. It also means that the horse can be integrated quickly into the yard’s worm control programme– which is hopefully a balanced approach of pasture management, faecal worm egg counts and strategic tests or treatments for the right worm at the right time of year.

Test before treating

It’s a good idea to have your new horse tested to assess his current worm burden before any treatment. A faecal worm egg count (FWEC) will give you an indication of adult redworm and roundworm parasites by measuring the number of worm eggs in a dung sample, reported as eggs per gram (epg). Remember though that a FWEC will not show the encysted larval stages of small redworm, tapeworm, bots or pinworm. There are specific antibody tests for encysted small redworm and tapeworm. Testing will start to build a picture of the worm burden carried and how the new horse’s worming regime can be best integrated into the yard’s general worm control plan.

Keep him in

Your new horse may continue to pass eggs for around a couple of days after you have wormed him so it’s important that you keep him off pasture for this period (~48hrs) to avoid contaminating the grazing. Even if he is going to be out on his own, it is still worthwhile to keep him off the field as he will still shed worm eggs onto the pasture and may re-infect himself when the worm larvae have matured.

Keep your fields clean

Once your new horse has been integrated into your worming programme with the other horses on the yard, remember the importance of good pasture management - it is inescapably linked to worm control strategy. Low stocking densities, daily ‘poo-picking’, cross-grazing with other stock such as sheep or cattle and the rotation and resting of pasture will reduce contamination and the exposure of the horses to infective larvae.

Check up on your worm control

Due to the challenges of a different routine, new horses often shed more worm eggs in their droppings than other horses on the yard. If the FWEC on arrival was high your vet may suggest taking another, 2 weeks after treatment, to check that the wormer has worked as expected (‘a resistance test’). After that, regular FWECs every 8-12 weeks (depending on previous count and the wormer used) will be a useful guide as to how he is coping with his new environment and the worm challenge. Always discuss your worm control plan with your vet or RAMA who will be able to advise on the best course of action for your new horse at every stage.

Looking after your new horse’s health from the outset will help make his transition to a new owner and a new yard more comfortable. It will also help him to perform at his best, which will be more fun for you and more fun for your horse!


Matthews (2008). Equine Vet. Educ. 20 (10) 552-560

Reinemeyer and Nielsen (2013) Handbook of Equine Parasite Control, p55





Wendy graduated from Bristol University in 1999. She then went on to complete a residency at Liverpool University and holds a European Diploma in Equine Internal Medicine. After working in practice for 13 years, she joined Zoetis in 2012 as the National Equine Veterinary Manager.

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