Reading various guides to the worming of your horse can be confusing and often appear to give conflicting advice. This is because there is not one single simple solution to the worming problem. At the Old Pound we frequently treat horses with colic, weight loss and diarrhoea caused by worms. This is due to the fact that worms are very good at evading control measures. One can take various approaches to worming a horse so that you will be able to see which strategy best suits your situation.

Points of consideration

• All horses are different.
Younger horses (less than 5 years) do not have as much immunity to worm infestations, making them more predisposed to developing heavy parasitic burdens. The same applies to older horses (greater than 15 years) especially those with concurrent illness.

• No universal
worming chemical.
There is no single horse wormer that will meet all worming requirements. Different types of worms need different chemicals to kill them. This is further complicated more by the small red worm (cyathastome). It is killed by most wormers when in adult form, living within the gut. However when the larvae burrows into the gut wall only two wormers are licensed to treat these, ‘Equest’ and a 5 day course of ‘Panacur Equine Guard’. However, more recently it has become apparent that there is increasing resistance to ‘Panacur Equine Guard’

• Level of infection.
It is important to realise that low levels of worm infection do not cause a problem and will help with immunity. It is those horses with heavy worm burdens that are more likely to suffer from disease

• Environmental issues.
Wormers may lead to insect and earthworm deaths in the pasture. The full environmental issues are unclear. Therefore wormers should be used only when needed.

• Continuous Use.
Continuous use of the same wormer or under dosing of individual horses can lead to resistance to that wormer. A weight tape should always be used to get a good idea of a horse’s weight.

Pasture is contaminated by eggs from horse’s dung. The horse will then eat grass containing the eggs and infective larvae which allows the worm to complete its life cycle within the horse. Therefore if you prevent horses from having contact with the contaminated feed or pasture, the risk of infection is reduced.

Factors increasing risk of worm infection

• High stocking density

• Presence of young horses

• Presence of horses with high worm burdens

• Warm damp weather

• Chain harrowing with no pasture rest period

Methods of reducing risk of worm infection

• Twice weekly removal of droppings from the pasture is proven to reduce pasture contamination.

• Rotation of pasture, or ‘resting’ pasture. A minimum of 3 months is recommended.

• Mixed grazing. Sheep and cattle act as “hoovers” for horse worm’s that can not survive in other species.  

Minimising pasture contamination by worming your horse

1. Interval dosing
Administering a specific drug at regular time intervals (approximately 6 - 13 weeks depending on manufacturer’s dosage intervals). This often means worming horses unnecessarily with low levels of infection. Some people will continue this regime when their horse is stabled over winter and droppings removed twice daily, even though the horse is at much lower risk of infection. This regime can lead to greater development or worm resistance to drugs, greater environmental contamination and greater cost.
However in pastures of high stocking density with no organised worming plan and regular newcomers entering the population this is often the only practical worming strategy.

2. Strategic dosing
Worming of horses seasonally to disrupt the life cycle of specific worms. For example strategic worming at turnout, in the middle of the grazing season and again in the autumn is an appropriate regime. However changes in weather pattern, the addition of new horses with unknown worming history and mixed age of grazing horses makes this strategy more difficult to maintain.

3.  Targeted strategic dosing
Strategic dosing is carried out, but all horses have faecal egg counts preformed prior to worming. Only horses with significant infections (>200 eggs/gram) are treated. Those with low infections are not. This leads to reduced development of worm resistance and less impact on the environment. Saving money in the long run and giving further ‘peace of mind’ to the owners.
However this can only work if all horses within the pasture are tested and treated appropriately. In pastures where there is a high turnover of horses it may be impractical to perform. The more pasture management methods of reducing the risk of worm infection employed, the more effective this strategy is.

There are 2 drawbacks to faecal egg counts

A) They do not pick up tape worm infections. Therefore ideally a blood sample is taken and sent to a specialist laboratory. If this is not possible discuss with us which wormer could be used.

B) Burrowing cyathastomes cannot be detected therefore at the start of this regime a red worm larvicidal dosing must be included.
At the Old Pound we will measure your horse’s faecal worm egg count and give you specific advice on the protocol and regime that best suits your situation. We only need about a tablespoon of fresh dung, so do not bring in bucket loads please!