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Is it ESSENTIAL to use a chemical ‘wormer’?

horse care horses worming Jan 29, 2021


How ESSENTIAL is it to use a chemical ‘wormer’ on your horse? - You can watch the video or read the article below for the same information.

Many horse owners think that using a chemical ‘wormer’ (an anthelmintic) is enough to control worms (parasites) in their horse. However, there are many reasons why you may need to think differently:

  • Chemical worming products (much like antibiotics) are becoming less effective over time due to overuse. The parasites are becoming resistant to the chemicals in them – which means they are not as effective. Parasites that survive after a chemical wormer has been used on a horse are RESISTANT to the chemicals. These parasites then pass on this resistance to future generations, creating larger populations of resistant parasites.

Chemical worming products (much like antibiotics) are becoming less effective over time due to overuse.

  • There are no new chemicals on the horizon to combat parasites. It is many years since new chemicals for parasites have been released. ‘New’ chemical worming products are simply the same old chemicals rebranded.
  • Chemical wormers are expensive. Especially if you use them as often as recommended. That recommendation mainly comes from chemical worming product manufacturers so of course they recommend that you use them often. Reputable companies are now recognising the damage that this over recommendation/use has caused. However, it is now part of the ‘culture’ of horse keeping that you should chemically worm your horse on a regular basis – so the belief is difficult to change.
  • Chemical wormers are dangerous and even deadly for other animals such as dogs, dung beetles and other wildlife (if they eat the paste that drops on the ground when a horse is being wormed or if they eat horse manure that contains it). It also has an effect on micro-organisms in the soil.

This does not necessarily mean that chemical wormers should never be used. They do still have a place (although in time reliable alternatives may be found), but they should ONLY be used when necessary rather than as a routine (i.e. every few weeks as recommended by many manufacturers). In fact, as already mentioned, it is directly because they have been overused in the past that they are no longer as effective.

Current thinking is that it probably benefits a horse to have a LOW worm count (rather than zero) as it helps build up their natural resistance.

The good news is there is a LOT that you can do to vastly reduce parasites from getting into your horse in the first place. This involves good pasture and horse management. Much of the advice that follows may go against what you have been taught in the past so bear with us!

You do not usually have to do ALL of these things to reduce parasites, just do the ones that you can, and you WILL see a reduction. This reduction can be tested by doing faecal worm egg counts (more on that later).


  • Rotate pastures – this practice, in conjunction with other good land management practices, is one of the most important steps for parasite reduction. It has so many other benefits – there is not the space to go into them here but you can sign up for this free mini-course Horses, Pasture and Grazing for more information - the course is just one hour long and consists of several short videos. By resting your pasture, some of the parasites will die before the horses return. They cannot survive without access to a horse to complete their natural lifecycle. They will also be more opportunities for the parasites to be eaten by predators or killed by inclement weather - wind (which dries them out), heat and cold.
  • Collect and compost droppings in small paddocks and loafing (surfaced) yards. Composting – when done properly – kills parasites and parasite eggs. This composted manure can then be used back on the land.
  • Harrow/spread manure on larger rotated paddocks (when the horses have been moved on to the next paddock). Yes, this does spread them around the land but it also helps to kill them as they are exposed to the weather. Spreading manure also has the added advantage of reducing or eliminating ‘roughs’ (toilet areas) which means there is more pasture available for grazing. On the other hand if you do not manage your land properly you can lose the use of more than 50% of it to this ‘dunging behaviour’ which is peculiar to horses.

Spreading manure also has the added advantage of reducing or eliminating ‘roughs’ (toilet areas) which means there is more pasture available for grazing.

  • Cross graze (mixed graze) whenever possible. This means to let other animal species graze the same land as the horses (usually after they have grazed the paddock). Parasites are by large ‘host-specific’ and most horse parasites are killed when picked up by other animals such as cows or sheep for example.

Cross graze (mixed graze) whenever possible.

  • Encourage and nurture dung beetles. These critters are the worlds manure management experts! – NOTHING you do in an attempt to manage horse manure comes close to what they do and gives the benefits that they do. They are a whole subject in themselves so look out for more info on them in one of our other articles or videos. Remember that some worming chemicals can kill dung beetles.


  • Use an effective worming paste only when necessary. It is better to use a broad-spectrum (and usually more expensive) product less often than a cheaper narrow-spectrum product more frequently.
  • Test your horse/s using a faecal worm egg test before you use a chemical wormer because in many cases you will not need one. It is not difficult to do a test and there are lots of videos online that show you how to do this. Although the test does not pick up on all the parasites it does give you an indication on the current level of your horse’s parasite burden. If you have a closed herd (no new horses joining the herd) you will not need to do this as often as you learn more. Again, look out for more info about this subject in one of our other articles. Generally, 20% of horses carry 80% of the parasites (in a given herd), usually very young, very old or unhealthy horses. Which means that not all of the horses in a herd will require the same chemical worming regime. Identifying which horses need it and when can cut your use of chemical wormers dramatically.
  • Avoid feeding on the ground if there is manure present. Feed in large feeders but try to keep the area around feeders particularly clean.
  • Do not overstock horse paddocks which will lead to high levels of manure and more parasites.
  • Chemically worm any new horses before they are released into a paddock/herd. If you can, keep them in a surfaced yard and collect the manure for three days afterwards. Bag this manure up and take it to the tip rather than add it to your compost heap. Do not use it to fertilize your garden as it will kill the earthworms etc.
  • If you acquire a new horse that looks particularly ‘wormy’ (pot-bellied, poor, scurfy skin etc.) get veterinary advice before using a chemical wormer on them as the sudden death of large numbers of parasites can be very dangerous for a horse (they can block arteries etc.). In fact, it is a good idea to get veterinary advice before worming any horse when you do not know their history.

I hope you have enjoyed this article, it is one of the Equiculture Essentials articles for members of our Facebook Group for novice horse riders and owners (there are also lots of equine professionals, as well as ourselves, to give help and advice) - anyone can join: hope to see you there :)

Jane xxx

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