Worming CPD March 2018


Explaining modern worming to less receptive customers

While SQPs are fully aware that guidance on the best ways to control worms has changed in recent years, some horse owners haven’t fully embraced the importance of moving with the times. Dr Wendy Talbot, national equine veterinary manager at Zoetis, looks at what’s changed and why. She also summarises the main points to convey to your customers to help them bring their worm control up to date.What’s changed and why?

Before the advent of faecal worm egg counts (FWECs) it was standard practice for a yard to blanket worm all horses every few months. Whether a horse needed a wormer or not it was given one, with the wormers rotated throughout the year. 

This method is now regarded as very old-fashioned and can in fact be counter-productive. Essentially, by continuing to use wormers in such an indiscriminate way we are perpetuating the problem of resistance; more worms will be able to survive the limited portfolio of drugs that we have. With no new drugs on the market this leaves us in danger of not being able to control the worm burden in horses.¹

Yet, some horse owners and yard managers still cling to blanket worming as it’s what they were brought up with, it’s easy to remember and understand and they have the apparent reassurance that every horse is receiving a treatment no matter what!

This group may believe the modern way is too fiddly or complicated but actually it’s very straightforward to grasp if we break it down into three lynchpin points:

• Tailor a specific plan for each horse, using any history you have.

• Conduct regular faecal worm egg counts to guide targeted dosing for redworm during the grazing season.

• Dose strategically for specific worms that don’t show in egg counts.¹ 

The importance of the SQP’s role

SQPs and vets play a fundamental role in ensuring that horse owners make the right choices about worming. But have you considered that some of your customers may not be aware of the role of the SQP? 

Perhaps you could carefully explain your position to these customers to enable them to understand that you have a special qualification? And that you have to attend lectures and prove your knowledge throughout the year in order to maintain your status as an adviser and prescriber of wormers? This should make them more receptive to what you have to say.

What seasonal worming advice should I give?

• Spring

Tapeworm don’t reliably show up in FWECs and should be targeted twice a year, usually in the spring and the autumn using a single dose of praziquantel or a double dose of pyrantel or a specific tapeworm test conducted.²

• March to October

Faecal worm egg counts (FWECs) should be used every 8-12 weeks to identify redworm (strongyle) eggs in dung during the grazing season from around March to October and horses treated according to the results.³

Faecal egg count reduction tests should be used during the grazing season to check that wormers are working properly. This involves taking a FWEC immediately before and two weeks after worming to assess the level of worm eggs being shed.¹

• Autumn

Tapeworm don’t reliably show up in FWECs and your second dose of the year should be given in the autumn using either a single dose of praziquantel or a double dose of pyrantel or a specific tapeworm test conducted.²

• Late autumn/early winter

Encysted small redworm don’t show up in FWECs and should be targeted in adult horses once a year in the late autumn or early winter using a single dose of moxidectin or a five-day course of fenbendazole. There is evidence of widespread resistance in small redworm to fenbendazole, including the five-day dose, so a resistance test is recommended before using it.⁴

Bots (don’t show up in FWECs) should be treated annually after the ‘first frost’ using a single dose of ivermectin or moxidectin.¹

• All year round

Keep a record: Encourage your customers to keep thorough records so that they have a history of the wormers used and the results of tests. They can share this information with you or their vet to make sure the correct parasite threat has been targeted at the correct time and to avoid overuse of the same types of wormer.

Keep pasture clean: Poo picking, ideally every day, will reduce the overall worm burden and thus the need for excessive use of wormers. Some of your customers may be in a position to create smaller paddocks so that each field can be alternately grazed, harrowed and rested. Cross-grazing with sheep and cattle is also effective at reducing horse parasite burdens on the pasture as they ‘hoover up’ the worms without being affected although in some areas liver fluke may be a concern. 

• Dose for other worms

In addition to these seasonal threats, it’s important to ensure at least one of the doses given throughout the year is effective against large redworm (moxidectin, ivermectin or a five-day course of fenbendazole are indicated). Pinworm, liver fluke and lungworm may be a concern for some horses² – remember to mention these to your customers to see if their horses may be at risk. 

• More frequent treatment for youngstock

If your customers have foals or weanlings they will need to be wormed more regularly than their adult counterparts; as a rough guide, they should receive a minimum of four worming treatments per year. Roundworm (ascarids) are the primary concern in young foals. FWECs are useful to indicate if this parasite is present, as well as guiding the need for extra treatments for redworm.²

• Weigh before worming

Ideally you should advise your customers to weigh their horses at least once a year using the accuracy of a weighbridge. It’s particularly easy to under-estimate the weight of our horses, which can result in under-dosing and lead to resistance. 

Resistance is when a drug doesn’t work as well against a population of worms as it did when it was first used, enabling some worms to survive treatment.

Understanding the active ingredients in wormers

Moxidectin and ivermectin
These are both part of the most recent class of wormer to come to market - macrocyclic lactones. Ivermectin was introduced in the 1980s and moxidectin in the 1990s. They are licensed to treat adult and larval stages of roundworms and bots, with moxidectin being the only single dose active that effectively treats for the encysted larval stages of the small redworm (cyathostomin).2 

Pyrantel belongs to a different class of wormer from the others. It has efficacy against adult roundworms and against tapeworm when used at double dose. It is very useful in young horses and during the grazing season for adult horses to control the adult stages of small strongyles during the grazing season, although some resistance has been reported.¹,⁴ 

Effective against adult roundworms, fenbendazole also has a claim against larval stages, notably the encysted stages of the small redworm, but only when extended dosing is used. This wormer has been in use since the 1960s and as such there are significant levels of resistance to this class of wormer. It remains a very effective drug for ascarids in foals or pinworm in all horses.⁴,⁵ 

A specific chemical for the treatment of tapeworms. All ‘combination’ wormers contain praziquantel combined with an ivermectin or moxidectin².

1. AAEP (2016) Parasite control guidelines
2. Reinmeyer CR and Nielsen MK (2013) Handbook of Equine Parasite Control. Wiley-Blackwell.
3. Hallowell- Evans and Hallowell (2017) Vet Times, April 24
4. Matthews (2008), Equine Vet. Educ. p 552-560 
5. Nielsen MK (2016) Equine Vet. Educ. 28 (4) 224-231