Sustainable Worming

As Autumn approaches, it is the time of year that we reach for a wormer, to target encysted redworms and tapeworm, both of which cannot be detected on a worm egg count. Is this still the right thing to do for our horses’ health and for the health of the environment? During this article we will discuss this further, based on the current advice on worming, which reduces our reliance on anthelmintics*, without being detrimental to your horse’s health, but at the same time being mindful of our impact on the environment.

You may have noticed a change in the worming advice you are receiving over recent years.  Traditionally worming used an interval programme where anthelmintics (wormers) were given every 6-12 weeks regardless. We now understand this isn’t the best approach, not only for our horses but also for the environment. 

What is anthelmintic resistance?

To further understand your worming programme it is key to understand the challenges we face due to anthelmintic resistance.

A parasite is considered resistant to a wormer (anthelmintic) if it survives exposure to the standard recommended dose of wormer, this resistance can be passed on to subsequent generations of that parasite too. This is a growing problem in the UK horse population and one we need to take seriously, otherwise we won’t have wormers that work when we really need them, which will lead to an increase in illness and death caused by untreatable parasite burdens. This is the collective responsibility of every horse owner.

The Impact on the Environment

If we can reduce our reliance on wormers, we can not only slow the progress of anthelmintic resistance but also be more sustainable.
Over the years we have become more aware of our impact on the environment, and we know that wormers and other ectoparasiticides (such as topical fly repellents and lice treatments) can have unintended negative impacts on non-targeted wildlife such as insects by residues ending up in the environment. Examples include chemicals being passed out in the faeces onto the pasture or being washed off the coat into the water course. These residues can then affect insects and could be a contributing factor in the decline in insect populations and diversity, by affecting their survival, breeding capacity and activity.  The chemicals in wormers and other ectoparasiticides are important but we have a collective responsibility to use them carefully. One of the insects that can be adversely affected are dung beetles.

Why are dung beetles so important?

Dung beetles’ existence relies on animal dung! The UK has approximately 60 species of dung beetles, but sadly almost 50% are categorised as nationally scarce or threatened to some degree. Dung beetles have been studied far more extensively with their relationship with cattle than horses. Research into the dung beetle has shown that they are beneficial to cattle through reducing flies and increasing nutrients in the soil. We also know that the dung beetle is a key indicator of a healthy micro-habitat ecosystem. Although dung beetles don’t have the most glamourous job, they are a critical part of our ecosystem, by recycling the dung from the pasture back into the soil, improving the quality and structure of soil, reducing compaction and fixing nitrogen. They will also help to reduce the fly population and parasite burden on a pasture by removing the dung, another benefit for your horse. If we look after these insects in return, they will help with the poo picking and offer soil improvement, all for free!

Methods for reducing the reliance on wormers:

Moving to a selective worming programme will help reduce the amount of wormer we use; this will have benefits for our horses and the environment and slow the development of anthelmintic resistance. A selective worming programme is a risk-based approach to worming based on diagnostic testing (worm egg counts, tapeworm and small redworm testing). There is a balance to be struck between too much worming and too little, balancing the risk of resistance with the risk of disease. Following a selective worming plan can minimise the risk of disease whilst reducing the risk of resistance developing.

• Target your worming, rather than indiscriminately giving a wormer. Regular faecal egg counts will allow you to target those horses and ponies that need worming. Faecal egg count tests should be performed 3-4 times a year, but this will vary depending on the weather, your horse, and the risk of worms on your yard. The general advice is that those with a low worm egg count (less than 200 eggs per gram) do not need worming. For higher worm burdens, if you need to give a wormer, ensure you are using the right wormer to target the parasite you want to eliminate based on the season and stage of its lifecycle. Your Vet or SQP (Suitably Qualified Person) will be able to advise you further as to which wormer is the most appropriate.
• Check for resistance after worming by performing a faecal egg count reduction test, this means you repeat the faecal worm egg count 10-14 days after the wormer was given to ensure it has been effective and resistance has not developed on your pasture.
• Post-worming you might want to consider stabling horses for 48-72 hours to reduce the risk of toxic wormer residues ending up on the pasture and contacting dung beetles and other insects.
• Unfortunately worm egg counts do not detect all types of worms, the common ones that are not seen in faecal egg counts in horses are tapeworms, pinworm and encysted redworms, other testing methods are now available for these.
• Tapeworms can be detected using a blood test or a home saliva test, which will assess the risk and help you decide whether worming is needed. Tapeworm testing should be performed every 6 to 12 months, in Spring and Autumn.
• Pinworm, causes an itchy bottom, and the eggs can be seen under the microscope following a simple tape strip test (simply sticking Sellotape to the area, then your Vet can examine under the microscope).
• In the last few years, a new blood test has become available for encysted redworm. This has reduced the need for many horses to be given a routine moxidectin treatment in the Autumn, meaning you can now worm based on a risk-based approach. Your Vet will be able to give you more specific detailed advice on worming, based on the individual horses age, lifestyle and risk.
• Pasture management plays a key role in managing the worm burden.
  1. Regular poo picking paddocks to remove droppings from the field before the eggs hatch which usually takes 4-5 days. There is a balance here to allow dung beetles a chance to use the faeces, but the good news is many dung beetles prefer fresh droppings, up to 48 hours old, meaning the infective larvae won’t have had a chance to hatch by the time it is picked up.
  2. Co-grazing with ruminants such as sheep will be beneficial as they don’t share the common parasites.
  3. Rotate grazing and allow fields to rest for at least 3 months between grazing.
  4. Don’t overstock your field with too many horses.
• Muck piles! You will all know how much muck a horse can produce in a day – the average horse can produce approximately 7 tonnes a year! Your muck pile is another place that can impact the environment and your horse’s health. Don’t keep your muck pile in or near your horse’s field – this could risk reinfecting your pasture (and horse) with parasites, with some worm larvae able to move 3 metres! The area around a muck pile, particularly if poached or with effluent run off, is also a prime breeding ground for midges (not helpful for those sweet itch sufferers). The effluent can also have other negative impacts on the environment such as water quality.
• Have a quarantine protocol for any new equine arrivals, not just for infectious disease but also for parasite burdens.
• Check out CANTER (Controlling Antiparasitic Resistance in Equines Responsibly). CANTER is a fantastic new initiative providing a coordinated approach for the equestrian community to combat wormer resistance. CANTER has some excellent resources to help you to understand your horse’s parasite risk.

Using a combination of these techniques has so many benefits, for you, your horse and the environment. Using regular worm egg counts can not only reduce the risk of anthelmintic resistance but it could also save you money in the long run. 

Worming advice will vary depending on so many factors, including the age of your horse, any history of illness, stocking density, pasture management and other risk factors such as regular new arrivals, so it is recommended to speak to your Vet to help you set up a worming programme based on your individual circumstances, which should be reviewed annually.

So this Autumn, don’t just automatically reach for the wormer, think about your whole worming programme as not only can this be beneficial for your horse and reduce the risk of anthelmintic resistance, it can also help protect the environment.

Tips for getting the best sample for a worm egg count:

• The sample should be as fresh as possible, ideally less than 12 hours old. If there is a delay between collecting and it reaching the vet or lab, keep it in the cool.
• Don’t take too small a sample – wearing gloves, ideally take a generous pinch from 5 different faecal balls within the same pile.
• Fill the container to the top, or squeeze air from the bag, to ensure as little air as possible remains.
• Don’t forget to label it properly!

* Definition of Anthelmintics: Anthelmintics are commonly known as wormers. They are a drug used to kill or expel internal parasites from the horse. In the UK there are 5 main wormer drugs licenced for use in the horse: Fenbendazole, Pyrantel, Ivermectin, Moxidectin and Praziquantel. There are no new horse wormers in development, making it vital to protect the ones we have from resistance.