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There are over 100 types of worms that affect horses of all ages.

The main parasites that affect horses are:

Small Strongyles – This type of worm is becoming more resistant to wormers.

Large Strongyles – Causes significant health problems in horses of all ages.

Tape Worms – Little significance unless in very large numbers

Bots – Not a worm but still an internal parasite

Round worm – common in young horses such as foals and weanlings

Pin worm – more of a nuisance - often see tail rubbing

Strongyloides – common in foals

Most worms spend a part of their lifestyle outside the horse. Over 99% of equine parasites live on the pastures.


Worms are responsible for a whole range of health problems ranging from weight loss, appetite loss, poor/rough coat, poor growth, lethargy, anaemia, diarrhoea, colic and death in extreme cases. A horse with a parasite infestion does not necessary have to show the dull, potbellied appearance. These days the shiniest coated horses can still have a worm burden.


As with all diseases prevention is better than cure and all horse owners should aim for this. There are two approaches to ensuring control:

1. Reduce parasites in horses

2. Control numbers in pastures

The best way to control worms in horses is to implement a successful worming program using an oral wormer every 6-8 weeks.


There are many brands of wormers available to purchase, however you should pay attention to the active ingredient as there are two main types - “MECTINS” and “AZOLES”.

MECTINS are generally allwormers, containing abamectin or ivermectin, this type normally kills all worms including bots and tapeworms. This is the most commonly used wormer and has been used for years and said to have no known resistance.  Some examples include Equimax, Equimec, Promectin Plus, Ammo, and Razor.

AZOLES are ingredients such as oxfendazole and oxbendazole, known as the rotator wormers that do have known resistance to some worms and do not kill all the worms. This means that if you use this product all the time some worms will not be killed and a problem could still exist. Examples include Oximinth, Equinox, Strategy T. HOWEVER, rotating wormers is very important to prevent MECTIN resistance developing.

For effective worm control you should select a suitable worming program that rotates between wormers to prevent worms becoming resistant to a particular wormer. There are some factors that you should consider when choosing a wormer.


1. What is the active ingredient – is it a mectin or azole product?

2. How much will one tube treat ie 600kg, as some wormers such as Equest only treat 575kg so is this enough for your warm blood probably weighing 700kg.

3. If you are going to use a rotator wormer what parasites doesn’t it control? For example Strategy T is a great rotator but does not do Bots so is not an ideal wormer in spring and autumn when bots are about.


Ensure all horses are wormed at the same time

Foals can be wormed from 4-6 weeks and should be wormed 4-6 weeks until reached one years old.

Faecal egg counts are a cheap way of ensuring your worming program is working.

Keep paddocks reasonably clean and not overstocked.

Make sure your horse is not being underwormed – it is better to give too much than not enough.

Straight AZOLE ingredient wormer have high resistance so  try Equest (Moxidectin) or Strategy T (Oxfendazole & Pyrantal)  as they are as they have effective kill rates comparable to the “Mectins”.

There are also new wormers with triple ingredients available such as Equimax Elevation. These would be ideal for new horses as an initial drench, whereas the worming history is unknown.


Proper pasture management is very important and often neglected. Remember 99% of worms will spend some of their lifecycle in pasture.

Try not to overstock paddocks

Keep the paddocks clean of manure by picking regularly.

New horses should be isolated and wormed before being introduced to other horses.

Rotate the paddocks with other stock such as sheep or cattle occasionally.