A complete guide to worming your horse

Controlling the worm burden is an important part of every horse owner's care routine. Petplan Equine veterinary experts Gil Riley and Juliette Edmonds discuss why worms can be dangerous and how best to manage them.

Why worm a horse?

‘A major worm burden can cause damage to the gut, leading to colic or 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, the way owners manage worms in horses has changed, due to problems with ‘wormer resistance’. Instead of worming their horses at set times of the 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 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 the way owners manage worms has changed. 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 whether 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 provide you with 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 veterinary expert 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 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 and don’t produce eggs. Tapeworms only produce eggs at certain times, so won’t always show up in FWEC. They can be detected by a blood or saliva test.

Symptoms of heavy worm burden in horses

• Weight loss
• Dull and/or rough coat
• Poor body condition and/or a pot-bellied appearance
• Loss of (or decreased) appetite
• Lethargy and reduced ability to exercise
• Diarrhoea
• Colic
• Coughing
• Tail rubbing (especially with pinworms)
• In severe cases, anaemia

However, it’s important to remember that some horses can have a heavy worm burden but not exhibit noticeable symptoms, so regular egg count testing is crucial.

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 passed on 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. Worming the mare during pregnancy will also help reduce numbers transferring to the udder.’

Which worms can horses get?

• Small redworms
• Roundworms
• Pinworms
• Threadworms
• Tapeworms
• Bots

How often should you worm a horse?

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 five-day course of Fenbendazole (will not target 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 roundworms also, use a combination wormer.
  
• Summer (May-Aug): Carry out FWEC and worm if necessary with Fenbendazole or Pyrantel.

How to worm a 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 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 steps to remember:

1. Put a headcollar and lead rope on your horse.
2. Prime the wormer syringe to the correct dosage for your horse’s weight.
3. 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.
4. With your left hand, slip the syringe into the corner of their mouth and push the plunger down.
5. 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 them a syringe of something tasty, such as apple sauce or molasses, so they don't associate a syringe with the wormer.

Should you stable after worming a horse?

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.