5 Things to be aware of when worming your horse

5 Things to be aware of when worming your horse image of a horse in a field

Ensuring your horse is correctly wormed is one of the most important duties you have as a horse owner; worms can otherwise lead to various health difficulties including diarrhoea and colic, and even fatalities if the condition is serious enough. Fortunately there is plenty of advice and help available in the equine community for treating worms in their various forms. In this article, we’re going to share with you some extra tips and pieces of advice for helping to get the most out of your horse worming programme.

Horses have evolved alongside worms in their natural environment, and in fact it is not the case that horses should be worm free – when worms are present but in low numbers, the immune system of the average horse can keep them in check, furthermore a small worm burden can help a horse develop a degree of natural immunity to the various kinds of worm infections that they may pick up. Nevertheless, worms can be a problem if they begin to multiply, so make sure you’re up to speed with the latest advice from your vet.

Only worm when necessary – otherwise, test

Historically, it was common for worming routines to be carried out regularly according to the season, as a precautionary measure. This is now understood to not be the ideal way to undertake worming, primarily because regular exposure to wormers allows the worm populations to build up a resistance to them and subsequently lowers their effectiveness (also, exposing your horse to worming drugs more often than necessary is generally not a good idea)

As an alternative, common advice is to undertake egg counts using faecal worm egg count kits at regular intervals to monitor for the presence of worms, and only undertake worming if there is a high level of eggs in the faeces.


Giving the correct dose

When giving wormers to your horse it’s tempting to estimate the correct dose by eye, or going on gut feel. Don’t do this! Research has shown that weight estimates by eye can vary by as much as 30%, which could lead to you either considerably over or under – dosing your horse. Overdosing, though relatively safe, will have little additional beneficial effect, whereas underdosing may lead to resistance building up in surviving worms.

To accurately gauge your horse’s weight, make sure that you either use a weighbridge or weighing tape, and be aware that slightly rounding up (e.g. giving 550kg worth of dosage to a 525kg horse) should be perfectly safe.

Your horse may not take well to worming, in which case (if you use a syringe to administer the dose) you can practice by giving him or her something tasty via the syringe (such as molasses) to reduce the likelihood that your horse associates the worming syringe with the wormer. Many horses will have a tendency to spit out at least part of their dose, which even when a small amount is missed can have a serious underdose effect – if your horse is prone to this it may be something to take into account when you calculate the dosage, or alternatively different means of administration may be preferred.

Probiotics and gut health

As important as worming is, it’s also essential to make sure other aspects of your animal’s health don’t go uncared for. One such area is gut health; as wormers can be quite strong drugs they may have a side -effect on the animal’s gut bacteria. A probiotic that is safe to use with a wormer will help to ensure a good balance of bacteria in the gut and help to prevent gut problems.

Maintaining a healthy environment

There are a number of actions that can be taken to reduce the incidence of worms and eggs in the environment, which in turn can have a positive effect on horse health. Actions we would recommend taking include:

  • Rotate pastures, ideally for at least three months. This helps the ground to recover, and gives strong sunlight and hard frost a chance to reduce egg counts.
  • Regular removal of droppings from paddocks and grazing land – this should be done at least weekly, and will greatly help to reduce the ability of worms to pass from the droppings onto the grass and subsequently on to other animals.
  • Avoid overcrowding – egg build up can also be controlled through not overcrowding pastures; a good rule of thumb is that 1.5 acres per horse should be sufficient.
  • Pasture sharing – sheep and cows are generally not susceptible to worms that are parasites to equine animals, so any eggs consumed by them will not develop. This can help to safely remove eggs from the local environment.

Resistance issues

Previously, we’ve mentioned that it’s important to try and prevent resistance to wormers by only using them when necessary. One reason why this is particularly important going into the future is that there are no new anthelmintic drugs currently in development. What this means is that the existing drugs available are gradually becoming less and less effective, with no obvious solution on the horizon.

Not all dewormers are effective against all types of worms, so make sure the brand of wormer you choose contains the correct active ingredients to treat the type of worms your horse is infected with. Your vet will know the right type of wormer for your horse.


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