Autumn/Winter Worming 

Whilst most of us understand the need to ensure that our horses do not develop significant worm burdens, there is evidence to suggest that many of us are not treating our horses in the most effective way. With an increasing risk of resistance to wormers, it is vital that we adopt a proper targeted worming programme to protect horses and ponies from the threat of irreversible damage. 

Why is a targeted worming programme important? 

  • Because of the increasing resistance to the active ingredients used in wormers
  • So that we do not worm our horses when it is unnecessary to do so, which is better for our horsesand helps prevent the development of resistance
  • So that we can target the right worms at the right time of the year

In the autumn/winter, we should treat our horses for: 

  • Tapeworm (if necessary following a tapeworm saliva test) - Autumn
  • Encysted small redworm larvae – Late autumn/wintera
    fter the first frost
  • Large redworm and bots - Autumn/winter

Which type of wormer is appropriate will depend on the results of a tapeworm test. 

What are tapeworms?

Tapeworms are the biggest worms to affect horses in this country. While the most common type can grow up to 20cm long, there is a much rarer type that can grow to a whopping 80cm in length!

Tapeworms are white, flattened, segmented worms that rely on the harvest mite to help them complete their lifecycle to infect horses; the mite ingests tapeworm eggs from dung and the horse inadvertently ingests harvest mites when eating forage. The larvae then develop into adult tapeworms in the horse’s digestive system. They can result in a number of health-related problems, ranging from loss of condition to colic.

TapewormTapeworms won’t reliably show up in a standard faecal worm egg count.  This is because the tapeworm eggs are contained within the body segments of the tapeworm, which intermittently break off to be passed out in droppings.  It is sometimes possible to pick up some tapeworm eggs on a faecal egg count but because of the intermittent shedding and containment in body segments, absence of eggs seen does not rule out tapeworm infection.  Therefore, even if your horse has a negative faecal worm egg count it could still have a tapeworm burden.

We can test for tapeworm using a saliva test or a blood test.

What is a Tapeworm Saliva Test?

  • It is a test which measures the antibodies to the tapeworm parasites that are present in the horse’s saliva. Unlike the other method of testing which involves a blood test, owners can take the samples for the test themselves without the need for a vet.
  • Saliva is taken from the horse’s mouth using a simple swab collection kit. Horses should not have eaten, drunk or been exercised for 30 minutes before sampling to stabilise salvia concentration levels.
  • The swab is returned to the manufacturers for testing using a pre-paid envelope. The results will give a score and determine whether worming for tapeworm is required.
  • Results are reported to the lab at B&W if the test was purchased from us or provided under the Horse Health Programme.

A tapeworm test kit is available to buy from B&W Equine Vets or, if your horse is registered on the Horse Health Programme, a test kit is supplied to you in the autumn as one of the benefits.

The test can remain positive for up to 4 months after tapeworm treatment. Talk to your vet as to whether your horse needs to be treated if this is the case.

What are encysted small redworm and what are the dangers?

Small redworm larvae can encyst within the horse’s gut wall throughout the year – especially in autumn and winter. Typically, sudden mass emergence of larvae will occur in spring, damaging the gut, which can cause diarrhoea and colic1. This condition is known as larval cyathostominosis and has a mortality rate of up to 50%.1

Hidden within the gut wall, encysted small redworm larvae can account for up to 90% of the redworm burden in a horse2.

Encysted Small Redworm

Control needs to be focused on all stages of the parasite’s lifecycle, with specific attention paid to the encysted larvae.3

1. Love S, et al. Vet Parasitol 1999; 85: 113−122. 
2. Matthews JB. Equine Vet Edu 2008; 20(10): 552–560. 
3. Nielsen MK. Vet Parasitol 2012; 185: 32–44.

You can watch a video about why encysted small redworm larvae are a serious health threat to your horse here: Dangers of encysted small redworm larvae

Why is it not necessary to carry out a faecal worm egg count at this time of year? 

For most times of the year, whether we need to worm our horses and with what type of wormer, should be based on the results of a faecal worm egg count (FWEC), ideally carried out every 12 weeks.  

However, in the autumn/winter season, it is recommended that you treat your horse for encysted small redworm which cannot be detected by a FWEC. Treatment should be after the first frost using a wormer containing moxidectin, which also treats redworm and bots, which is why it is not necessary to carry out a FWEC at this time of year.   

If the results of a tapeworm test suggest that you need to treat your horse for tapeworm as well as encysted small redworm larvae, a wormer containing both praziquantel (to treat tapeworm) and moxidectin will be needed. 

Why do we wait until after the first frost to worm our horses in the autumn/winter?

  • This is so that re-infection from larvae on the pasture is minimised.

How can I ensure that I give the correct dose?

When worming your horse, it is very important that you give the correct dose. Not giving enough will not only reduce the effectiveness of the wormer but also aid resistance to it. Most wormers are very safe but accurate dosing is probably more important for young animals as their weight is often more difficult to estimate. Ask for help from your vet if this is the case.

Further information and instruction on weighing your horse can be found at:

Weighing your horse before worming


We offer faecal worm egg counts, tapeworm saliva tests and have a range of wormers available at very competitive prices. Contact your local B&W Clinic for prices and further details.

Why getting worming right is easy with the Horse Health Programme

Get the best preventative health care for your horse for only £13.99 per month, or £155.88 per year.

The Horse Health Plan includes an autumn tapeworm test, an autumn wormer and four faecal worm egg counts as some of its many benefits, making effective and targeted worming as easy as possible for you.

Contact your local B&W Clinic to register or go to for further details.

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