Horse Worming – How To Guide

Horse Worming – How To Guide

What are worms and why do we worm?

Worms are parasites that interfere with the equine digestive system and in some cases can make your horse extremely ill or in very extreme cases, death can result. Worms are an ongoing battle that is only getting harder with an increase in the levels of drug resistance and warm, wet summers and milder winters leading to an increase in worm prevalence. Symptoms of a heavy worm infestation can include

  • Diarrhoea
  • Colic
  • Sudden weight loss
  • The appearance of a ‘pot belly’
  • Heavy scratching of the tail (associated with pinworm)

These symptoms can be signs of other illnesses and so a vet should be consulted if you notice any of these, especially if your horse has recently been treated for worms. These symptoms can be of particular concern in very young and very old horses and so the importance for worm control in these animals is of even higher importance.

Common types of worm

Large Strongyles

As the larvae of these worms migrate through the digestive tract they can cause damage to arterial walls, impact on circulation by causing blood clots and possibly cutting off the blood supply to the intestine which can lead to severe pain and tissue death. These worms require management all year round.

Small Redworms

These worms make up the majority of a horse’s worm burden and are becoming all the more common as our climate changes and becomes milder. The reason that these worms can cause such a huge problem is that part of this worm’s life cycle involves becoming encysted in the gut wall and during the colder, winter months they remain encysted until the temperature begins to increase in the spring. As the weather warms and the worms emerge they can cause damage to the lining which can then result in colic.


Also known as large roundworms these worms don’t usually affect older horses as an immunity is developed at around 18 months old. They can cause a blockage in the gut of younger horses which can lead to a lack of nutrients, therefore resulting in poor condition and diarrhoea. These worms mature in the lungs of the young horse and can result in scarring of the tissue which can affect respiratory function and performance in later life ­ this is obviously of particular importance if you are hoping to compete your youngster in the future!


Rarely a cause for any clinical disease, these are particularly unpleasant to see. They lay eggs on the coat of the horse over the summer which are then picked up as they groom in order for the larvae to mature in the stomach and be excreted at the end of the winter.


The tapeworm is of the most concern in the autumn months when infective numbers peak. Tapeworm eggs are hard to locate on faecal egg counts but can be identified on a blood test from your vet or more recently on new saliva tests which can clarify whether or not tapeworm are present.

Worm Counts and Worm Prevention!

Owning horses makes life busy enough but it is a good idea to take the time to manage your worming programme with the use of worm counts and only using anthelmintics (wormers) when the count is high enough to require it. There are three types of worm count to test your horse

1) Faecal egg count – A faecal sample is taken and the worm count estimated based on the eggs seen in the faeces. This is a useful test however it does not give an indication of any encysted worms or tapeworm eggs (though if a tapeworm egg is seen you will be notified). If less than 200 eggs per gram, it may not be necessary to worm, though dependent on the time of year, it may be advisable to worm for tapeworm and/or encysted worms. You should speak to your local vet or SQP for more advice.

2) ELISA Blood test - Used for the detection of tapeworms.

3) EQUISAL Saliva test – A more recent test that measures the level of tapeworm antibodies to determine the tapeworm burden.

Using worm counts and wormers in this way is considered to be the most effective way to manage equine worm burdens and is known as targeted strategic dosing. For more information on worm counting, click here.

Some other ways to manage and lower the risk of worm infestation are as follows:

Rotation of pasture – This allows the fields to rest. The idea here is that in severe conditions (frosts and hot, dry weather) the number of larvae on the pasture will be reduced and so you should aim to rest the pasture at key times to ensure optimal results.

Mixed grazing - As the worms are specific to the horse, sheep and cattle should consume the worms on the pasture without being affected, thus reducing exposure to equines grazing in the same area. It should be noted however, that any other livestock that are turned out will need to be on their own individual worming plan regardless of any other management techniques used to keep worm burdens to a minimum.

Removal of droppings – Poo picking! Nobody’s favourite job but this can be a massive help in the reduction of your horse’s worm burden. This should be performed twice weekly. A reduction in paddock size can be beneficial here.

What should you use and when?

So you have navigated the world of worm counting, got your gloves on and taken the poo out of the field and yet you find you still need to use a wormer.

What now? If you think you need to worm then you need to speak to your vet or a registered SQP at your local retailer as wormers are veterinary drugs which must be prescribed. If ordering wormers online then you must answer questions which allow the correct wormers to be prescribed.

An SQP is a ‘Suitably Qualified Person’ who must pass a set of exams, have a general knowledge of animal health and the legal system in order to become registered with AMTRA to sell wormers. SQPs must also keep up to date with any new information and research by participating in continuing professional development to ensure the most accurate information is passed on to the customer.

As a rough guide, seasonally you should worm for the following

Spring - Worm for tapeworm and small redworm

Summer – Small redworm only

Autumn - Small redworm, encysted redworm, tapeworm.

Winter – Small redworm, encysted redworm, bots.

It is advisable to change the drugs used to lower the risk of resistance so again, you should speak to a qualified person about what is best for your horse. If using worm counts, the use of anthelmintics may be avoided, which means less drugs going in and less hassle for you!

Handy Hints!

  • Make a note of what you have used and when. This will help when finding the best wormer for your horse.
  • Monitor your horse’s weight. Weighbridges are best but if this isn’t possible then use a weight tape to ensure the correct dosage is given. It is also useful to make sure your horse is at the correct size as health can be affected if over or underweight.
  • Giving wormers to your horse can be a challenge, try mixing into a portion of feed and then feeding the rest when the wormer has been eaten or sneak it in by putting the wormer in a jam sandwich or a cored out apple.
  • Try feeding a course of pre and probiotics to maintain gut health after giving a wormer as any drug can have a negative effect on the gut flora. This is of particular importance if your horse is showing signs of clinical disease to prevent any further loss of condition.


Some of the products available for the treatment of worms can be seen below. Each wormer must be prescribed for the individual to prevent any adverse reactions.

Equimax­ - A broad spectrum wormer containing praziquantel and ivermectin. Comes in paste (treats up to 700kg) or flavoured tablet form (treats up to 800kg).

Eraquell/Eqvalan ­ - Ivermectin based wormers. Eraquell comes in paste (treats up to 700kg) or flavoured tablet form (treats up to 800kg) and Eqvalan is paste only (treats up to 600kg). These wormers treat for large and small strongyles, lungworm, pinworm, ascarids, hairworms, threadworms and bots.

Strongid P/Embotape - Pyrantel embonate wormers. Both will treat for tapeworm with a double dose and at the single dose level will treat for large and small strongyles, pinworms and large roundworms.

Equitape - Praziquantel. Worms for tapeworm only. Treats up to 600kg.

Equest - Moxidectin wormer. Broad spectrum wormer which also treats for encysted redworm but does not treat for tapeworm. Treats up to 700kg.

Equest Pramox - Moxidectin and Praziquantel wormer. Broad spectrum wormer as with the Equest but also treats for tapeworm. Treats up to 700kg. It is advised this wormer is held back to be used in autumn and winter months.

Panacur Guard - Fenbendazole. Given over the course of 5 days, this is the safest option for those with uncertain worming histories or those which have not been wormed for a considerable amount of time. This is to ensure that any encysted worms come out of the lining gradually rather than all at once to avoid the occurrence of colic.

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