Equine vet's complete guide to worming your horse

The idea of wriggly worms infecting our horses makes our skin crawl, and for good reason. Not only can they leave our horses feeling under the weather, they can also cause a lot of damage.

Why worm your horse?

'A major worm burden can cause damage to the gut leading to colic and diarrhoea, and in some severe cases, can be life-threatening,' says Petplan Equine veterinary expert Gil Riley.

So when it comes to worms, prevention is better than cure. Gil recommends that all horse owners follow a strict worm management routine to help protect their horses from the damage caused by worms.

Managing worms in horses using faecal worm egg counts

In recent years, we've changed the way we manage worms in horses due to problems with 'wormer resistance'. Instead of always worming every horse at set times of year, more owners are using faecal worm egg counts (FWEC) and a targeted worming approach to create a reduced worming programme.

Why use worm counts?

'Originally, wormers were purgatives and flushed the worms out of the system, but now, they kill them,' explains Gil. 'However, due to using the same ingredients in wormers for many years, worms are becoming resistant and with no other wormers being developed, there may come a time when there are no effective wormers available.'

That's why we've now changed the way we manage worms. Instead of using wormers indiscriminately, Gil recommends that horse owners use faecal worm egg counts (FWEC) throughout the spring and summer months when eggs are present in their horse's poo to check if their horse needs a wormer. As owners, this means we're not putting unnecessary chemicals into our horses' bodies and giving the wormers we do use a better chance of remaining effective into the future.

How to perform a worm egg count

Your vet can perform FWEC on your yard, or you can send a sample off to specialist laboratories who send you a kit – just ask your vet for details.

'We gather a 1g sample of poo per horse and it must be as fresh as possible,' says Petplan Equine ambassador and vet Juliette Edmonds. 'We then dilute the poo in a saturated saline solution and look at it under the microscope, measuring the number of eggs per 1g of faeces. We're not looking for zero eggs as a small amount of under 250 eggs per 1g of faeces is a manageable amount. A few worms don't do any harm and actually help to keep stimulating the horse's immune system. Anything over 250 eggs per 1g of faeces will require treatment.'

Worm egg counts only show up small roundworm eggs and are done through the spring and summer months because in the winter months, small roundworms go into a dormant state so won't be producing eggs. Tapeworms only produce eggs at certain times, so won't always show up in FWEC. They can be detected by a blood test or saliva test.

When to use worm counts

We recommend that horse owners perform FWEC every eight weeks from spring through to autumn, but it does depend on individual circumstances.

'FWEC frequency depends on your yard and personal situation,' says Juliette. 'Smaller yards, with small numbers of horses, which follow a strict pasture management routine of poo picking and paddock rotation may require slightly less testing.'

Worm counting foals and young horses

Young horses or older horses with lowered immune systems may be required to be worm egg counted and wormed more frequently. Young foals, for example, have no immunity to threadworms which can be passed from the mare. Infection can then leave them weak and susceptible to diarrhoea and anaemia.

'Natural immunity to threadworms usually develops by six months of age,' explains Juliette. 'But until then, foals should be wormed against threadworms as early as four weeks old and worming the mare during pregnancy will help reduce numbers transferring to the udder.'

Which worms can horses get?

●        Small redworms

●        Roundworms

●        Pinworms

●        Threadworms

●        Tapeworms

●        Bots

Annual worming schedule

Autumn (Sept-Oct): Carry out a saliva test for tapeworm. If positive, target tapeworm with a wormer containing Praziquantel or an elevated dose of Pyrantel.

Winter (Nov-Feb): Target encysted small redworm with a Moxidectin product. This will also kill botfly larvae. Alternatively, use a 5-day course of Fenbendazole (will not target any botfly larvae).

Spring (Mar-Apr): Test for tapeworm again and treat if the test is positive. Target tapeworm with a product containing Praziquantel or use an elevated dose of Pyrantel. If your horse needs worming for roundworm too, then use a combination wormer.

Summer (May-Aug): Carry out FWEC and worm if necessary, with Fenbendazole or Pyrantel.

How to worm your horse

You’ve received your worm count results and your horse needs to be wormed. Once you’ve identified the wormer you need, here’s what to do next.

Check your horse's weight

'Before giving your horse a wormer, it's important that you have an accurate weight measurement so you know how much to give your horse,' says Gil.

'Under-worming can add to the resistance issue, so it's important you get the dosage right. It's very unlikely that you will overdose on a wormer – they have very safe levels and low toxicity.'

Give your horse the wormer

Wormers come as a paste in a syringe that you can syringe straight into your horse’s mouth. Most horses will accept their wormer quite happily. Here are a few important points to remember:

●        Put a headcollar and lead rope on your horse.

●        Prime the wormer syringe to the correct dosage for your horse’s weight.

●        Stand on their near side, holding your right hand over their nose to keep their head steady. Just as you would to put a bridle on.

●        With your left hand, slip the syringe into the corner of their mouth and push the plunger down.

●        You may want to hold your horse’s head slightly upwards for a few moments, especially if they are prone to spitting their wormer out!

If your horse is difficult to worm, practise giving him a syringe of something tasty, such as apple sauce or molasses, so he doesn’t associate a syringe with a yukky wormer.

After worming: to turnout or stable?

You don’t need to keep your horse stabled after worming them. Worms will be killed by the wormer, so they won’t pass into your pasture through droppings.