Does my horse need to be dewormed in winter?

Deworming recommendations have changed A LOT over the past few years. We all used to follow an interval-based approach of deworming our horses every six to eight weeks or, for some, timing it with when the farrier came out. The problem with this approach is overuse of deworming (anthelmintic) drugs has led to widespread resistance. This means the drugs we use to kill the worms in our horses are no longer very effective! The other MAJOR problem is it looks like there won’t be any new drugs developed in the near future, if ever. It’s quite scary to think about resistant worms continuing to reproduce and create more and more super worms!

So, what do we do now? 

It is now recognised that 20% of horses carry 80% of the worm burden. Best deworming practice relies on the results of faecal egg counts (FECs) to identify the shedding category of your horse. Basically, you examine the horse’s manure under a microscope and count how many eggs there are. Horses with an FEC of <200 eggs per gram (epg) are considered to be “low shedders”, 200-500 epg “moderate shedders”, and >500 epg “high shedders”. A low shedder has a good natural immunity to parasites and therefore doesn’t require frequent treatment, whereas a high shedder may require more treatments to keep their worm burden under control.

There are a multitude of factors that determine the period between deworming treatments. Current best practice for deworming horses is to perform faecal egg counts (FECs) to determine worm burden and whether the individual needs to be treated.

The concept behind FECs is to slow down worm resistance to deworming drugs. Tailored deworming programmes need to be developed for each individual property. Performing FECs will also help you to identify whether there is a resistance problem on your farm. It is best to minimise the number of deworming treatments each year, only treat horses with a moderate to high shedding category and implement good pasture management and husbandry practices to reduce the risk of parasite transmission.

It is important to target parasites when environmental conditions are favourable for their survival on pasture. That is, when conditions are warm and moist (i.e. autumn and spring). Normally, it isn’t recommended to treat horses during winter when there have been significant periods of frost or during summer when it is very hot and dry, as the worm larvae aren’t viable during these periods. You would only deworm during this time if the horse returned a moderate to high FEC.

The general recommendation for adult horses is to treat every horse in late autumn with an ivermectin-based dewormer. Whilst the cooler weather means strongyle egg production decreases, this is the best time to target other types of parasites such as bot fly larvae and tapeworm. Kelato’s Evolve contains ivermectin and praziquantel and is the ideal broad-spectrum dewormer and boticide for autumn. Consistently low egg shedding horses only need to be treated once a year and autumn is the time to do it!

Remember, we can’t just rely on deworming drugs to control gastrointestinal parasites in our horses. It is essential to implement good management practices. Here are some recommendations to help slow anthelmintic resistance:

  • Pick up manure at least twice a week.
  • Avoid overcrowding (maintain low stocking densities in paddocks).
  • Avoid feeding horses off the ground (e.g. use feed bins).
  • Don’t drench in very hot or very cold weather.
  • Correctly dose horse according to weight.
  • Cross graze with cattle or sheep.
  • Quarantine and FEC newcomers on property.

So, should I deworm my horse in winter?

It depends! In most parts of Australia, egg production decreases in winter due to cooler conditions. However, we rarely experience cold conditions for long enough to seriously deplete eggs that winter-over on pasture.

As mentioned above, performing FECs will help you establish whether your horse is a “low” or “high” shedder. If your horse has a consistently low egg count, they won’t need an extra deworming treatment in winter, as they have a good natural immunity to gastrointestinal parasites. High shedding horses, determined by an FEC, may require an additional treatment in winter.

Remember, FECs will only identify strongyle and ascarid eggs. This method will not indicate tapeworm or bot larvae burden.


If you didn’t get around to treating your horse in late autumn, it’s recommended to treat with Evolve in winter to target bots and tapeworm. In terms of encysted strongyles, it is best to consult with your vet whether your horse requires treatment with Moxidectin or Fenbendazole.


Want to find out more? Head to the Evolve page, get in touch on 1800 Kelato or email