ETN’s series of CPD features helps SQPs (Suitably Qualified Persons) earn the CPD (continuing professional development) points they need. The features have been accredited by AMTRA, and highlight some of the most important subject areas for SQPs specialising in equine and companion animal medicine.

AMTRA is required by the Veterinary Medicines Regulations to ensure its SQPs undertake CPD. All SQPs must earn a certain number of CPD points in a given period of time in order to retain their qualification. SQPs who read the following feature and submit correct answers to the questions below will receive two CPD points.



September 2018

Worming down the line

With many consumers seeking advice via a phone call and purchasing wormers online, the Suitably Qualified Person’s (SQP’s) telephone manner has become all-important. Dr Wendy Talbot, national equine veterinary manager at Zoetis, looks at the legal obligations involved and how to make the best of communicating down the line.

The legal obligations

Whether your customers are in store, online or on the phone, it’s the SQP’s responsibility to prescribe before providing any retail supply of POM VPS medicines.

As well as asking the correct questions, it is crucial you guide your customer through the process so that ultimately they are also happy with their purchase. Questions include, but are not limited to: What age is the animal? What is its health status?

What previous treatments have been administered? What is the animal’s environment? (eg. stabled, at pasture etc.).

For those of you holding this important qualification, be proud of what you have achieved. Remember that your knowledge and prescribing advice is helping to preserve the efficacy of the drugs that we have. By prescribing a wormer, you’re ensuring that the customer uses the most appropriate product at the most appropriate time and at the right dose.

How Zoetis is supporting learning

Zoetis is committed to supporting learning across the equestrian industry. The company has recently set up a series of AMTRA accredited Equine Worming Online Continuing Professional Development (CPD) courses for SQPs A total of 1,257 SQP courses have been completed since they were launched in Spring 2017, with around a further 400 courses in progress.

For your customers

Zoetis has recently produced a sustainable worm control module for The British Horse Society’s Stage 3 Care Award Zoetis also has an educational website for horse owners containing a wide selection of articles on equine health and wellbeing, including parasite control.

Don’t miss a trick

Giving detailed and accurate advice can be challenging but if you take your time and follow these tips you should be able make the most of the opportunity to advise your customer responsibly. A positive conversation will help win their confidence and is likely to secure not only a sale but repeat business too:

• We all love to talk about our horses. Be animated and ask about the customer’s horses. They will appreciate your interest and will become more receptive to your advice.

• Briefly explain your role as an SQP and your credentials for advising on and prescribing equine wormers. This will position you as an authority on the topic.

• Try to avoid closed questions that invite a ‘yes’ or ‘no’ answer and may give misleading information. For example instead of asking ‘have you treated for encysted small redworm’? Try asking ‘which product did you last use to treat for, for example, encysted small redworm’? You may find that some people answer with products containing ivermectin or pyrantel, neither of which are effective against this parasite stage.

Build confidence to secure sales

Proactively offering season-specific advice can help to build trust and enhance customer satisfaction. The customer can complete the transaction having clearly understood the reasons why they are making a specific worming purchase. In this way they can be guided in terms of knowledge rather than by price.

By giving objective prescribing advice you are helping your customer protect the health of their horses in the most effective way possible. It’s likely you will be sought out for your advice next time and will become a trusted source of information on all things equine.


• Have you been clear why you have prescribed the product?
• Have you stressed the importance of delivering the right dose?
• Have you established that the customer knows how to administer the product safely and effectively?

Seasonal tips for horse owners

Spring to autumn (March to October)
• Every horse owner should work with their prescriber to tailor a specific plan for each horse using any history they have on the horse and considering the environment in which it is kept.
• Faecal worm egg counts (FWECs) should be conducted every 2-3 months during the grazing season to guide targeted dosing for redworm.1
• Foals and young horses are more susceptible to infection and disease and the parasites can differ from those of adult horses. Foals require treatment for ascarids twice in the first 6 months of life and careful and frequent monitoring for redworm from 6 months to 3 years.2
• Tapeworm – test or treat in late spring
• Pasture should always be managed carefully, with daily poo picking, regularly rested fields, and avoidance of over-stocking.

Late autumn/early winter
• Encysted small redworm (ESRW) don’t show up in FWECs and should be targeted in all horses (over approx. 6 months of age) once a year in the late autumn or early winter using a single dose of moxidectin or a five-day course of fenbendazole. Moxidectin is considered the treatment of choice.3 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 and should be treated annually after the ‘first frost’ using a single dose of moxidectin or ivermectin.5 Combining this treatment with the encysted small redworm dose by using moxidectin reduces the need to give additional doses of this important class of drug.
• Tapeworm doesn’t reliably show up in FWECs however a specific blood or saliva test for tapeworm can be conducted. Burdens are likely to be highest at the end of the grazing season.3 Dosing with a moxidectin/praziquantel combination at this time will treat for tapeworm, ESRW and bots in a single dose.
Being approachable, knowledgeable and confident, whether face-to-face, online or on the phone, will give your customers faith in your advice, making the prescribing process enjoyable, as well as effective for both of you.
Speak to your Zoetis Account Manager to find out more about the support Zoetis can provide.

1. Hallowell- Evans and Hallowell (2017) Vet Times, April 24
2. Matthews (2017) Helminth control programmes for equine yearlings at pasture Vet Times, Feb 27
3. Handbook of Equine Parasite Control (2013) Eds. Reinmeyer CR and Nielsen MK Wiley-Blackwell.
4. Matthews (2008), Equine Vet. Educ. p 552-560
5. AAEP (2016) Parasite control guidelines

AMTRA CPD explained

• AMTRA (the Animal Medicines Training Regulatory Authority) is an independent body whose task it is to ensure that the marketing and distribution of animal medicines in the UK is undertaken in a responsible manner by AMTRA qualified persons.

• AMTRA maintains registers of qualified persons, including Suitably Qualified Persons (SQPs), authorises training centres for course provision, provides information and advice for registered persons, monitors and accredits continuing professional development (CPD) for SQPs and regulates professional conduct.

• SQPs are permitted under the Veterinary Medicines Regulations to prescribe and supply medicines classified as POM-VPS and NFA-VPS.

• For more about AMTRA and becoming an SQP

September 2017

Current concerns in equine parasite control

By Rosie Naylor BVetMed MVetMed DipACVIM MRCVS, RCVS Specialist in Equine Internal Medicine and technical product manager (equine) at Virbac UK.

Anthelmintic drugs have been used extensively in the horse over the past 40 years.

During this time their widespread use has led to the development of anthelmintic resistance, particularly in cyathostomin [small redworm] populations. With no new anthelmintic compounds on the horizon, the responsible and strategic use of those compounds currently available is imperative to maintain their effectiveness.

There are three groups of anthelmintic drugs available to treat endoparasites in the horse. Benzimidazoles, such as fenbendazole, tetrahydropyrimidines such as pyrantel, and the macrocyclic lactones which include moxidectin and ivermectin.

Resistance occurs when parasites develop adaptations that evade the action of that particular drug. When these adaptations confer an evolutionary advantage, the prevalence of the resistant gene will increase.

Husbandry practices

There are many factors that increase the selection pressure for resistant worm, such as treatment frequency, the proportion of the population exposed to the treatment, exposure to sub-lethal doses when drugs are under-dosed and husbandry practices.

Whilst horses are exposed to several nematode species, the cyathostomins are by far the most prevalent (Relf et al 2013). There are over 50 species of cyathostomins that infect the horse. Third stage larvae (L3) are ingested from the pasture by the horse and these penetrate the wall of the large intestine. Within the wall of the large intestine, the larvae develop further and emerge to form adult worms within the intestinal tract.

In some situations, the L3 arrest their development or hypobiose, encysted within the wall of the intestine. The precise triggers for this are unknown, although climate, worm burden and immunity have all been suggested.

Re-emergence of encysted L3 results in extensive intestinal inflammation which can be associated with subclinical disease or severe colitis, known as larval cyathostominosis, a condition with a mortality rate of up to 50% (Love et al 1999).

Pyrantel and ivermectin are effective against adult cyathostomins and ivermectin is also effective against the non-encysted larval stages. Moxidectin and fenbendazole, however, are the only two anthelmintics with efficacy against the encysted larval stages of cyathostomins.

Growing concern

In the two products shown to treat encysted cyathostomin larvae, resistance is a growing concern.

Benzimidazole resistance in cyathostomin populations is widespread in the UK, with studies demonstrating resistance in 80-100% of the population (Rossano et al 2010).

There is also growing evidence that moxidectin resistance is emerging. A recent publication documented a reduced egg reappearance period following moxidectin administration, as low as 5 weeks in individual horses (Daniels and Proudman 2016).

Of further concern is a new study which identified faecal egg shedding within 6 weeks of moxidectin administration in 54 out of 261 adult horses, housed on 8 different premises within the UK (Tzelos et al 2017). The authors concluded that these eggs most likely came from adult worms that developed from mucosal larvae that survived treatment with moxidectin (Tzelos et al 2017).

Faecal egg counts

The incorporation of faecal egg counts into herd management programmes has led to the development of strategic worming regimes for horses.

By identifying and targeting treatment at horses with significant adult worm burdens, the overall use of anthelmintics has been reduced.

By allowing a significant portion of the worm population to remain unexposed to the drug, or in refugia, this has reduced the pressure for the development of resistance in these parasites.

Regular removal of droppings, has also been shown to correlate with improved treatment efficacy (Tzelos et al 2017).

Lack of reliable test

Unfortunately, the lack of a reliable diagnostic test to identify significant larval cyathostomin burdens currently limits such targeted strategies being applied to the management of cyathostomins in the horse.

Encysted L3 are a significant part of the parasite’s life-cycle and these would not be detected with a faecal egg count.

An IgG(T) ELISA blood test is currently under development (Dowdall et al 2002) and if successful will be a great asset in detecting pre-patent infections and targeting anthelmintic treatment to those individuals at risk.

At present, blanket treating all animals with a larvicidal product during the winter months, remains standard practice (Matthews 2008). Given the extensive prevalence of benzimidazole resistance, moxidectin is the only effective treatment option in many areas. This highlights the need to protect the use of moxidectin, as currently no alternative products are available for the treatment of encysted cyathostomins.


Cyathostomins pose a great threat to the equine population, with larval cyathostominosis a life-threatening condition.

The current practice of routinely treating all horses with moxidectin during the winter months is less than ideal. We await a reliable diagnostic test to be able to tackle this further.

Throughout the rest of the year, spring through to the end of autumn, the use of moxidectin should be avoided, to limit the selection pressure on cyathostomin populations (Coles 2009).

Strategic worming programmes using alternative drugs should identify and target affected horses. In addition appropriate treatment for tapeworm, with either praziquantel or a double dose of pyrantel, in autumn/spring is recommended.

Daniels, S. P. and Proudman, C.J. (2016) Shortened egg reappearance after ivermectin or moxidectin in horses in the UK. Vet J. 218 36-39.
Dowdall, S.M., Matthews, J.B., Mair, T., Murphy, D., Love. S., and Proudman, C.J. (2002) Antigen-specific IgG(T) responses in natural and experimental cyathostominae infection in horses. Vet Parasitol. 106. 225-242.
Love, S., Murphy, D., Mellor, D. (1999) Pathogenicity of cyathostome infection. Vet Parasitol. 85 113-21.
Matthews, J.B. (2008) An update on cyathostomins: anthelmintic resistance and worm control. Eq Vet Ed. 20 552-560.
Relf, V.E., Morgan, E.R., Hodgkinson, J.E., Matthews, J.B. (2013). Helminth excretion with regard to age, gender and management practices on UK Thoroughbred stud farms. J Parasitol. 44. 507-14.
Rossano, M.G., Smith, A.R., Lyons, E.T. (2010) Shortened egg reappearance periods in naturally infected horses treated with moxidectin and failure of lavicidal dose of fenbendazole to reduce faecal egg counts. Vet Parasitol. 173, 349-352.
Sangster, N.C. (2001) Managing parasiticide resistance. Vet Parasitol.98 89-109.
Coles, G. (2009) Anthelmintic resistance in equine worms Vet Times.
Tzelos, T., Barbeito, J.S.G., Nielsen, M.K., Morgan, E.R., Hodgkinson, J.E., Matthews, J.B. (2017) Strongyle egg reappearance period after moxidectin administration and its relationship with management factors in UK equine populations. Vet Parasitology 237 70-76.

Encysted redworm

Adult redworms in droppings

Rosie Naylor BVetMed MVetMed DipACVIM MRCVS, RCVS Specialist in Equine Internal Medicine and technical product manager (equine) at Virbac UK

AMTRA CPD explained

• AMTRA (the Animal Medicines Training Regulatory Authority) is an independent body whose task it is to ensure that the marketing and distribution of animal medicines in the UK is undertaken in a responsible manner by AMTRA qualified persons.

• AMTRA maintains registers of qualified persons, including Suitably Qualified Persons (SQPs), authorises training centres for course provision, provides information and advice for registered persons, monitors and accredits continuing professional development (CPD) for SQPs and regulates professional conduct.

• SQPs are permitted under the Veterinary Medicines Regulations to prescribe and supply medicines classified as POM-VPS and NFA-VPS.

• For more about AMTRA and becoming an SQP

January 2017

Encysted small redworm - how to help your customers get the message

Despite the best efforts of SQPs and vets to help horse owners understand and implement the right worm control plan, it seems we still have plenty of work to do, reports Dr Wendy Talbot, national equine veterinary manager at Zoetis.

New data from this year’s National Equine Health Survey (NEHS) has shown that almost a third of horse owners are using the wrong wormer or one to which there is widespread resistance, when they treat their horse for encysted small redworm.1

The figures are worryingly similar to last year’s results, which suggests that the messages about responsible worming are simply not getting through.

What can we do about it?

The challenge for us as vets and SQPs is to explain the grave health risks and resistance issues posed by encysted small redworm if owners continue to make mistakes about worming.

To help you, we have produced a reminder of the top ten points to raise with your customers when selling a wormer to treat encysted small redworm, together with answers to some of the most frequently asked questions.

• Severe infestations of encysted small redworm larvae can lead to fatal disease.
• Faecal worm egg counts (FWECs) do not show the presence of encysted small redworm.2
• Encysted small redworm are the dormant larval form of the small redworm (cyathostomins), which are the most common parasites to affect horses.
• Encysted small redworm ‘hibernate’ in the horse’s gut wall and do not produce any eggs so this is why a FWEC will not reveal them.
• In the spring the hibernating larvae suddenly ‘wake up’ and emerge, often in very large numbers, causing damage to the gut wall. Typically this occurs in late winter/early spring, especially in young horses.2,3
• Initially there may not be any symptoms of encysted small redworm so you may not know your horse has got them until he starts to show signs of a problem later on.
• Severe infestations of encysted larvae can lead to a distinct disease syndrome known as ‘larval cyathostominosis’. This causes diarrhoea, severe weight loss and colic and can be fatal. The condition has a 50% mortality rate.3
• All adult horses should be treated for encysted small redworm in the late autumn or early winter each year regardless of the results of any faecal worm egg count.2
• Only two active ingredients are licensed to treat encysted small redworm: a single dose of moxidectin or a five-day course of fenbendazole,
• There is widespread evidence of resistance in small redworm to fenbendazole, including the five-day dose so a resistance test is recommended before using it.2

Answers to commonly asked questions

What is the main parasite that can affect my horse?

The most common parasite to affect horses today is the small redworm (small strongyle/cyathostomins), which, in its encysted form can cause diarrhoea, rapid and severe weight loss, as well as life-threatening colic.

What happens if I overdose my horse?

If you think you have overdosed your horse you should always contact your veterinary surgeon for advice. As with all drugs, it is important to dose accurately and in accordance with the manufacturer's recommendations or those given by your vet, especially in low bodyweight animals or foals.

What about underdosing?

Underdosing should not do any immediate harm, but the wormer may not be as effective as an accurate dose, therefore the horse may be left at risk of parasitic-related disease. In addition, by exposing the worms to the drug but perhaps not at a sufficient dosage to kill all of them, you can have issues with development of resistance. These worms that survive treatment may pass on their more resistant traits to subsequent generations driving resistance to that drug.

How important is it to weigh horses? Can't I just guess his weight or give him a whole syringe?

Establishing a horse's weight by guessing and not using a weigh tape or weigh-bridge, means you risk giving your horse an overdose or insufficient dose of wormer. By not giving your horse enough treatment for its bodyweight you risk giving a sub-lethal dose of the drug, which will not be enough to kill all resident worms - under-dosing (see above).

If I don't use a whole syringe, can I use the remaining wormer next time?

Always refer to the packaging of the product to see how long the product can be used once open. Remember the product must be stored according to the package instructions and not accessible to children, or other animals. Empty syringes must be disposed of safely.

Can I find out if my horse is resistant to a worming product?

It’s not actually the horse that’s resistant to a worming product, it’s the parasite population carried by the horse and on the pasture it grazes that is no longer susceptible to the drug used. The active ingredient of the horse wormer kills the sensitive parasites in the population, but those parasites not affected go on to create new generations of worms that become resistant to the drugs used. Inappropriate, frequent dosing or under-dosing can cause resistance to occur, as can the effectiveness of the wormer.

It’s important to discuss your worming plans with your vet or Suitably Qualified Person (SQP). They will assess the likely challenge of resistance versus the threat of clinical disease to your horse before prescribing the most suitable wormer for the parasite being targeted. Your vet or SQP may wish to carry out a faecal worm egg count reduction test to assess the resistance status of worms within the population your horse is exposed to. This involves taking a faecal worm egg count before worming and then taking another a couple of weeks after worming to check the effectiveness of the wormer used. It is most usefully performed on a herd basis (at least six horses in the same grazing group).

National Equine Health Survey reveals that horse owners are still using the wrong wormer for encysted small redworm.

While more than 77% of respondents to this year’s National Equine Health Survey intended to treat their horse for encysted small redworm, of the 89% of respondents who could remember what they used only 68% had correctly used moxidectin either as solo therapy or in combination with praziquantel (compared with 64% in 2015). 5.2% had used a 5-day course of Fenbendazole, a product which is licensed but for which resistance has been widely documented.2 However, of the remainder, 19% had used ivermectin (22.5% in 2015) and 7.5% had used other products, none of which are licensed or effective against ESRW.

We all know that worming can be a bewildering and confusing subject, even to the most conscientious of owners. It makes the job of a trusted professional even more important but with your informed and intelligible advice we can help them get it right and keep their horses healthy.


1. NEHS The National Equine Health Survey, conducted by the Blue Cross and supported by Zoetis, was completed by 5635 horse owners and keepers in May 2016, with records returned for 16,751 horses. The survey contained questions on general horse health, care and management and was validated by Professor Josh Slater of the Royal Veterinary College.
2. Matthews (2008) Equine Veterinary Education, p 552-560
3. Dowdall S.M.J. et al (2002) Veterinary Parasitology 106, 225-242

Severe infestations of encysted small redworm larvae can lead to fatal disease.

SQPs can help owners get their worming right and keep their horses healthy.

Encysted small redworm ‘hibernate’ in the horse’s gut wall; a faecal worm egg count will not reveal them.

AMTRA CPD explained

• AMTRA (the Animal Medicines Training Regulatory Authority) is an independent body whose task it is to ensure that the marketing and distribution of animal medicines in the UK is undertaken in a responsible manner by AMTRA qualified persons.

• AMTRA maintains registers of qualified persons, including Suitably Qualified Persons (SQPs), authorises training centres for course provision, provides information and advice for registered persons, monitors and accredits continuing professional development (CPD) for SQPs and regulates professional conduct.

• SQPs are permitted under the Veterinary Medicines Regulations to prescribe and supply medicines classified as POM-VPS and NFA-VPS.

• For more about AMTRA and becoming an SQP

September 2016

Optimising parasite control

By Chris Taylor BVSc MRCVS,
Technical director, Virbac Limited

The basic aim of 3D Worming – which stands for direction, dosage and delivery - is optimising parasite control via:

• The appropriate use of wormers
• Good pasture management
• Monitoring the effectiveness of worming
• Avoiding high parasite burdens
• Preventing or delaying anthelmintic resistance
Remember…The only way to ensure the correct approach is via the core SQP responsibility, which is asking the right questions – each time, every time.


What is the best direction to take when worming a horse?

The basic questions are:

• Is the horse one of the 20% with a high worm burden or not? In any multiple horse establishment there will be enormous variations in the worm burden of individuals. In general, it is likely that 20% of such horses will have higher burdens then the rest.

• When a wormer is needed, what is the best way to dose and which product and at what time of year?

The two main objectives are:

• to prevent disease
• to reduce pasture contamination
So the main aim is targeted treatment.

First of all you need to establish whether the horse is likely to have a significant worm burden so you should advise a faecal worm egg count (FWEC) before treatment and again 14 days post treatment. A FWEC does not provide any indication of how many worms are infecting a horse but how much the horse is contaminating the pasture. Horses with high counts generally need more regular treatments with wormers; those with low counts (FWEC results of < 200 eggs per gram) may only require key strategic treatments.

But do remember that FWECs can mislead:

• They do not detect the encysted stages of small redworms.
• They do not detect tapeworms.
• They provide little or no information on levels of parasite infection over the winter months.
• FWECs are not directly correlated with the number of worms.
• There can be inaccuracies if the faeces are not collected and stored properly – fresh faecal samples are mandatory as eggs can hatch before the count is performed yielding a false negative result.

Which product and when?

Tapeworm treatments may be given in Spring and autumn using either praziquantel or pyrantel. Bots should be treated in November/December using ivermectin.

Encysted cyathostomes (small redworm) need to be treated between November and late January/early February using moxidectin or five day fenbendazole.

Worming should be strategic at other times (through the grazing season) using ivermectin/fenbendazole.

Expert recommendation is to reserve moxidectin only for once yearly treatment of cyathostomes. A quote from a well-known parasitologist, Dr Gerald Coles, (In Vet Times No 51 December 2009): “Since moxidectin is so valuable because of its activity against inhibited larvae, it is best confined to use for an autumn or early winter treatment.”

Targeted strategic worming in practice

The following flow chart summarises the direction needed.

Picture Dosage

Giving the correct dose is absolutely vital as under-dosing leads to:

• Poor efficacy – health risks and owner dissatisfaction.

• Exposure of worms to sub-lethal dose which encourages resistance.

The accurate weight of the horse must be known prior to prescription so you should always recommend a weighbridge if available or a weigh tape and use of the standard weight calculation formula below.

Picture You should always bear in mind that horse owners are notoriously bad at weight ‘guesstimation’.

On average, horse owners underestimate weight by 20% and frequently more. It is also strange to note that over estimation of weight is extremely rare!

You need to be aware of ‘convenience’ too – a significant number of horses weigh over 600kg, but the tendency is to use just one syringe for heavy horses.


The correct dose must be delivered properly. One of the biggest everyday problems with syringe wormers is ‘spit out’.

In a study on 480 horses at the French Ministry of Defence, 22% of them spat out a significant amount of the wormer administered. And those horses spat out between 29% and 68% of the contents of the syringe wormers they were given. Indeed, ‘spit out’ can be a problem, even for experienced equestrian handlers.

So, what’s in a syringe?

Bear in mind that the plastic of the barrel used in equine syringe wormers is very thick; it’s designed to withstand chewing! This means that the tube containing the worm paste or gel is very narrow. Basically, syringe wormers contain between 5 and 10ml, or only one to two teaspoonsful.

Spit out, therefore, is not only a potential poor efficacy problem – it can also be a significant safety problem as dogs will be poisoned should they ingest wormer residue from the floor. It is an inescapable part of your prescribing duties to warn owners about such situations as well as the safe disposal of used and part-used syringes.

For horses that are known to be ‘difficult’ with syringe wormers, there is a viable alternative. Ivermectin and ivermectin/praziquantel wormers are available in palatable (apple grounds, not flavour) tablet form. Presented in a simple dose form - one tablet per 100kgs and eight tablets per tube, they can be presented in feed and are usually well accepted provided the horse does not see the owner putting the tablets in the feed!

AMTRA CPD explained

• AMTRA (the Animal Medicines Training Regulatory Authority) is an independent body whose task it is to ensure that the marketing and distribution of animal medicines in the UK is undertaken in a responsible manner by AMTRA qualified persons.

• AMTRA maintains registers of qualified persons, including Suitably Qualified Persons (SQPs), authorises training centres for course provision, provides information and advice for registered persons, monitors and accredits continuing professional development (CPD) for SQPs and regulates professional conduct.

• SQPs are permitted under the Veterinary Medicines Regulations to prescribe and supply medicines classified as POM-VPS and NFA-VPS.

• For more about AMTRA and becoming an SQP


January 2016

Management of gastrointestinal parasites on stud farms

By Douglas Palmer BVMS MRCVS,
Norbrook veterinary advisor for northern UK.

The challenge of managing parasites on a stud farm is four-fold:

• High infection pressures due to a relatively high proportion of the equine population being youngstock: they are more likely to be high shedders of eggs onto pasture, and more likely to succumb to clinical disease
• Increased resistance to multiple drugs in parasites of interest
• Increased animal movements on and off the stud farm increase risk of importation of parasites, with or without drug resistance, necessitating stringent quarantine policy
• Limited number of products licensed for use in pregnant mares and young foals

Traditionally, interval dosing was used to meet the needs of the stud farm i.e. all horses were routinely wormed at set intervals throughout the year. However, this system promoted over use of anthelmintics and increased selection for worms possessing anthelmintic resistant genes. Due to the development of resistance in worm populations affecting equids, an interval-based approach is no longer sufficient to control internal parasites and a targeted regimen is recommended.

The targeted approach to worm control

In a targeted plan only those horses showing a high worm burden (demonstrated by a faecal egg count) are treated with an anthelmintic product. This ensures that a proportion of worms on the stud farm are left unexposed to anthelmintics, either because they are on the pasture, or residing within untreated animals.

This slows down the selection for resistant worms, because the higher the proportion of worms which are not exposed to anthelmintic, the more dilution there is of the population of resistant worms on the stud premises. The result of this is that the majority of worms remain susceptible to anthelmintic treatment and the proportion of resistant worms is kept to a minimum. This concept is termed ‘in refugia’.

On the stud farm a targeted regimen needs careful management as parasites can build up quickly in the environment and young foals have no natural immunity to worm infections. In severe cases of worm infestation foals can develop diarrhoea, weight loss and sometimes colic which can be fatal. The main objectives of a targeted plan concern negating the likelihood of young susceptible animals suffering clinical disease, whilst also trying to slow the development of resistant populations of worms on the premises. Resistance is a one-way street; once the worm population on farm is resistant to a class of anthelmintics, there is no going back!

In this article we look at the main worm species of concern on the stud farm, the control measures that can be put into place and where anthelmintics can fit into this regime.

Parasite species affecting the stud
Strongyloides westeri (threadworms)

These are found in the small intestine and are less than 1cm in length. Only female worms are found in the intestine where they lay eggs produced by asexual reproduction. Parasitic larvae enter horses and foals by ingestion from the pasture or skin penetration; foals can also become infected via the mares’ milk.

Once ingestion or penetration of the skin has occurred, the larvae migrate to the lungs via the blood. They travel to the larger airways and trachea, from where they are coughed up into the mouth, then swallowed back down to the gastrointestinal tract. They mature to adults once in the small intestine and start producing eggs.

In older animals after penetrating the skin, they can accumulate in the subcutaneous tissue and then move to the mammary glands when lactation starts. Foals can therefore become infected through drinking the milk from the mother. Adult worms can start producing eggs in the small intestine of the foal from about one week after foaling.

Clinical signs of Strongyloides infection can be subclinical, but high burdens in foals cause diarrhoea and weight loss. Occasionally dermatitis can also be seen after larvae have penetrated the skin.

Foals not showing any symptoms of disease may also shed high numbers of eggs in their faeces in the first weeks of life, before they have established a solid immune response. Environmental contamination can therefore build up over a breeding season on a stud farm exposing later-born foals to a greater risk. Most anthelmintics, including macrocyclic lactones, e.g. ivermectin or moxidectin are effective against this parasite.

Parascaris equorum (ascarids)

This is thought to be the most significant worm for young foals. The adult worms are long (up to 40 cm) and white in colour. They live in the small intestine and produce large numbers of eggs in the foals’ faeces. These eggs are not infective until the larvae develop inside. For this to happen they need a warm humid environment and it usually takes several weeks for the larvae to develop. These eggs are sticky, very thick walled and can persist in the correct (cool and moist) environment for up to five years. They are also resistant to many disinfectants.

When the infective eggs are ingested they hatch and the larvae burrow through the intestinal wall and then travel to the liver. In the liver they cross into the blood circulation and travel to the lungs. After migrating through the lungs to the trachea they are coughed up and swallowed. Once in the small intestine they develop into adults and start producing eggs. Newborn foals can start shedding eggs in faeces within 12-13 weeks. High numbers of eggs can be found on pastures that are heavily stocked and used for youngstock for many consecutive years. Inadequate cleaning of stables can also lead to a build-up of eggs in the housing.

In older animals, particularly yearlings, no clinical signs are seen but they can continue to shed eggs in faeces which contaminate the environment and are an important link in the transmission of these worms.

Heavy infestations cause generalised malaise, poor growth, poor coat, diarrhoea, lowered resistance to other diseases and colic can also be seen. In severe infestations intestinal obstruction and perforation can occur resulting in the need for surgery. Lung damage caused by migrating larvae may result in fever, coughing and a nasal discharge.

Treatment is possible with macrocyclic lactones, benzimidazoles or pyrantel although resistance to several groups has been reported in the UK.

Cyathostomes (small strongyles or small redworm)

These form part of the strongyle group of worms. There are ten common species which have a direct non-migratory life cycle. Eggs pass into the environment via the faeces and under optimum conditions (shade, moisture and moderate temperature) these will hatch and become infective L3 larvae on the pasture. These larvae are then consumed and will enter the walls of the large intestine where they become encysted and remain in a small nodule for between 7-18 weeks before breaking back out into the intestinal lumen. Clinical signs associated with adult cyathostomins include ill-thrift, diarrhoea and anaemia. Resistance to all classes of anthelmintics in adult cyathostomes has been reported in the UK, particularly to benzimidazoles.

Mares are initially the main source of infection as they can carry appreciable burdens and pass on large numbers of eggs whilst potentially not showing any clinical signs. In areas such as the United Kingdom where the winters are cold and the summers are mild, large numbers of worms will build up over the spring and summer so that massive contamination of pastures with infective larvae occur in late summer and early autumn when young susceptible horses are present.

In heavy infections, emergence of large numbers of larvae over a short period causes inflammation of the large intestine with small ulcers where larvae have emerged, haemorrhaging and excess mucous production. Clinically, rapid weight loss, diarrhoea and colic can be seen. Unless treated early the prognosis is guarded.

Outbreaks of disease due to simultaneous emergence of cyathostomes commonly occurs in late winter or early spring, however this can happen at any time of year and may also be triggered by anthelmintic treatment. This disease process is known as larval cyathostomosis and can be seen in horses of all ages, most commonly in those less than 5 years old and older foals.

Larval cyathostomosis can be challenging to diagnose as faecal egg counts can be zero as it is the emergence of the encysted immature stages that cause disease. The inhibited mucosal stages are insusceptible to many treatments. All foals should receive treatment with moxidectin or five day benzimidazole at the end of the grazing season to reduce levels of infection with cyathostome larvae (2).

Anoplocephala perfoliata (tapeworm)

This parasite’s life cycle is more complex. The eggs are produced in the horses’ faeces within a tapeworm segment which disintegrates quickly releasing the eggs. These are consumed by forage mites and within the mite they develop into a cysticercoid larval stage in 2-4 months. These mites are then ingested by the horse and 1-2 months later the adult tapeworms are found in the intestines usually around the ileo-caecal junction and can cause ulceration and thickening here.

Heavy infestation may interfere with gut motility and cause colic. Diagnosing infections can be tricky as the eggs can be difficult to find in faeces. There are antibody tests that can be used on either blood or saliva samples. Treatment for tapeworm is usually with a pyrantel or praziquantel based anthelmintic. All horses and foals should be treated as a minimum at the end of the grazing season and again in the spring if blood or saliva testing has come back positive.

Additional strategies to reduce reliance on anthelmintics

In summary there is no definitive protocol that will be appropriate for every stud farm so stud managers, SQPs and vets should work together to develop a suitable and sustainable protocol.

Minimising infection pressure from the environment is paramount. Disinfection and regular cleaning of all stables and foaling boxes throughout the breeding season is essential. There are limited options for grazing management however cutting the roughs which offer protection for the larvae, or mixed or alternated grazing with ruminant species can help reduce contamination as the parasites are host specific.

Use clean paddocks for the youngest foals and avoid moving them onto pasture where older foals and yearlings have been. Removal of faeces twice weekly from all paddocks and daily from nursery paddocks is very effective provided heavy rainfall does not disperse the faeces first. This can be by hand or on tractor or quad-mounted mechanical devices.

New arrivals should not be mixed before having a quarantine period of three days and treatment with moxidectin.

Consider grazing management strategies, where possible, such as removing faeces from the paddocks and alternate or co-grazing with ruminants.

Appropriate treatment should be given to all foals for encysted cyathostomes and tapeworms at the end of the grazing season with a larvicidal dose of wormer and tapeworm treatment. Treatment for Strongyloides westeri and Parascaris equorum should be discussed with the animal health advisor (vet or SQP) as infection pressures will differ in separate management systems.

Regular faecal egg counts every 1-2 months from all stock(1) and antibody testing for tapeworm is essential to identify those shedding significant numbers of worms who should therefore be treated with anthelmintics. This will maintain a proportion of worms ‘in refugia’ who retain susceptibility to anthelmintics. Treated horses should not be moved onto clean pasture immediately as this will allow any surviving resistant worms to contaminate the fresh field.

When using an anthelmintic follow the manufacturers’ guidelines closely. Check that the product is licensed specifically for the age, sex and reproductive status of the individual animal that you are treating.

Use a weigh bridge or a weigh tape to ensure an accurate dose is given. Ensure the whole dose is taken.

If resistance is suspected in the population of parasites on a stud, the veterinary surgeon should be contacted to discuss performing a faecal egg count reduction test (FECRT).

In conclusion, traditional interval-based dosing previously adopted for all animals on stud farms, whilst simple and uncomplicated to administrate, is unsustainable, and has contributed to increasing reports of anthelmintic resistance in equine gastrointestinal parasites across the UK. Special attention must be paid to stud farm health planning, to develop a strategic worm control policy, to preserve susceptibility in worms on premises, whilst preventing outbreaks of clinical disease in youngstock.

1. Practical management of parasites on breeding premises, Proceedings from BEVA Congress 2015.

About the author

Douglas Palmer BVMS MRCVS qualified from the University of Glasgow Veterinary School in 2002 and has since worked in mixed practice in the north east of England. Douglas joined Norbrook in July this year as veterinary advisor for northern UK.

AMTRA CPD explained

• AMTRA (the Animal Medicines Training Regulatory Authority) is an independent body whose task it is to ensure that the marketing and distribution of animal medicines in the UK is undertaken in a responsible manner by AMTRA qualified persons.

• AMTRA maintains registers of qualified persons, including Suitably Qualified Persons (SQPs), authorises training centres for course provision, provides information and advice for registered persons, monitors and accredits continuing professional development (CPD) for SQPs and regulates professional conduct.

• SQPs are permitted under the Veterinary Medicines Regulations to prescribe and supply medicines classified as POM-VPS and NFA-VPS.

• For more about AMTRA and becoming an SQP


September 2015

Equine worming – updating your advice

Blaise Scott-Morris BVSc MRCVS

Advising on worming regimes can be complicated especially as there is no ‘one size fits all’ solution. Challenges presented include ensuring an accurate estimation of weight, trying to ensure the horse receives the full dose it is prescribed and combating increasing resistance to worming treatments. This article aims to give an overview of the parasites that we are facing and how we can assist our clients throughout the year to keep their horses happy and healthy.

Worms of importance
The importance of different equine gastrointestinal parasites varies with a horse’s age, the time of year and the parasites migratory pathway within the horse. Cyathostomins, commonly known as small redworms (See figure 1) are considered one of the most important equine parasites worldwide (3,4) and a particularly important parasite to consider in the spring. After ingestion, the larval stages of the parasite become encysted once they reach the large intestine. Up to 90% of encysted larval cyathostomins may become ‘inhibited’ in this encysted state and can live in the large intestinal wall for up to two years. In the spring these larval stages emerge en masse causing severe damage to the intestinal wall resulting in diarrhoea, colic and possibly even death (4).

Worms with migratory pathways such as Parascaris equorum, commonly known as roundworms (See figure 2) can contribute to gastrointestinal and non-gastrointestinal signs. P. equorum migrates via the liver and lungs, causing signs such as coughing and nasal discharge. The eggs are extremely resistant to external environmental conditions so can sustain the cycle from one year to the next through multiple batches of foals. Infected foals can pass millions of eggs daily. As foals grow, the volume of larvae that reach the small intestine, and the number of eggs produced dramatically decreases, conferring good age immunity after approximately the first year of life (2, 6). P equorum infection in young horses can be significant, causing ill thrift, poor growth, weight loss, colic and intestinal impaction or perforation leading to death (See figure 3).

Intestinal parasites such as Anoplocephala perfoliata (tapeworms) and Strongyles (redworms) (See figure 4) are commonly an underlying cause of colic in adult horses. Parasites cause colic through damage at their site of attachment or migration, either to blood vessels or intestinal mucosa and furthermore physical blockage of the intestine, which may lead to an impaction or, in the worst case, intestinal rupture.

Oxyuris equi, more commonly known as pinworm, can be particularly challenging to control due to its location within the gastrointestinal tract. This parasite has a unique lifecycle, living in the caecum and large colon. Female worms then migrate a short distance to the rectum, stick their back ends out and lay eggs in clumps on the perianal region. There is significant perianal irritation and the eggs can be seen as yellow white gelatinous streaks. Most commonly owners initially see their horse persistently rubbing their back end on objects such as fences causing a ‘rat-tail’ appearance.

Risk factors and diagnosis
A horse’s lifestyle should be assessed for factors which would place it in a high or low risk category when it comes to exposure to worms and subsequent worming strategy.

High risk situations include horses on larger yards and sharing grazing, especially if there is a high turnover of horses with unknown worming histories. If all horses on the yard can be wormed at the same time with the same wormer, strategic dosing can be used with any new animals on the yard wormed immediately and not turned out for 24 hours unless the worming history is unknown and full worming may induce further problems. In this case a more targeted approach may be warranted which avoids killing all the worms at once as this can lead to further complications for the horse. If cooperation on a yard is not possible then interval dosing or targeted strategic dosing are both options depending on owner commitment. Most importantly ensure there is a strategy of some sort in place! Other risk factors would include horses that travel to shows a lot or compete if they have access to grass or different forage.

On smaller yards or those with a stable horse population targeted strategic dosing may be more easily achievable. This involves determining the level of parasite infection a horse has. There are several ways of performing this: a faecal worm egg count (FWEC), such as the FECPAK system (Techion Group Ltd), can be used to assess the roundworm burden during the summer grazing season. The standard threshold for retreatment on a FEC is a minimum of 200 eggs/g; retreatment is necessary to keep a low level of pasture re-infectivity and continue to decrease parasite burden in the herd (1). Tapeworms can be diagnosed via a blood or saliva test. The saliva test can be performed quickly and simply by the owner and then returned in the post to a lab who will analyse the sample and email the result.

The targeted strategic dosing strategy also supports the role of refugia in response to resistance. By leaving some worms in refugia i.e. unexposed to wormer treatments, you dilute the population of worms which will develop resistance. This can be achieved by using FWEC to decide which horses are treated therefore limiting the number of horses treated, using a wormer that only kills adult worms thereby leaving the young emerged larvae essentially in refugia (after assessing the risk of mass emergence on a case by case basis), or managing the larval numbers on pasture via poo picking.

Direction - Worming strategy options
There are several options to consider when advising on worming in different situations as outlined above. Depending upon how and where the horse or horses are kept.

Worming Strategy Definition Advantages Disadvantages
Interval Dosing Regular dosing performed every 4 to 13 weeks (depending on type of wormer) May be the only option on multi owner livery yards if there is no coherent worming
programme in place
Many treatments are unnecessary and the overuse of wormers encourages resistance
Strategic Dosing Specific treatments given at certain times of year based on the parasite lifecycle and
the risk of disease
Helps to reduce,unnecessary treatments. Helps reduce risk,of resistance. Makes worming more cost-effective Requires all,owners on the yard to co-operate as all horses grazing together should be,treated together.
It’s possible, that some horses may need more frequent dosing.
Some treatments may still be unnecessary
Targeted Strategic Dosing Specific
treatments determined by FWEC and/or tapeworm ELISA tests (blood/saliva)
Avoids unnecessary treatments and greatly reduces the risk of resistance Costly
to set up initially, but as less wormers are used, this balances out. Requires
all owners on the yard to co-operate in testing and treatment

Dosage - Treatment considerations
It is vital to ensure horses are receiving the correct amount of wormer for their weight; however, in reality, this presents as problem. When a horse’s weight is estimated, on average, the estimate is approximately 20% below the actual weight. Also a horse’s weight will fluctuate considerably at different times of year depending upon its workload so the same weight should not be assumed all year around.

Delivery – Treatment considerations
A second factor to consider is the importance of a horse receiving the full dose of wormer. In each syringe of wormer is approximately one or two teaspoons of paste containing the total dose of the active ingredient. Any ‘spit-out’ can represent a significant volume of the overall dose being lost and horses not receiving the correct dose. Under-dosing has two consequences; firstly, the product will not work as it should, leaving customers dissatisfied; and secondly, it can contribute to the rapid development of resistant worms.

There are now more options when considering how to dose a horse for worming. In addition to a traditional syringe of paste, tablets are also available. Tablet wormers such as Equimax Tabs or Eraquell Tabs (Virbac) allow the flexibility of wormers being given as a treat, with a treat or mixed in with the food. This presentation aims to address the issue of ‘spit-out’, giving flexibility to owners with horses who are more challenging to worm.

General pasture management such as poo picking is important in the control of all equine intestinal parasites alongside a well implemented and controlled worming strategy. For other worms such as Oxyuris equi the most important measure is management not worming strategy. Ensuring owner awareness and vigilance will ensure horses with a possible infection are spotted early. This can then be addressed through hygiene measures in the environment and washing of the horse’s back end.

In conclusion, a few simple steps can be taken to make advising on worming a stress free experience for both you and your client. Ensure that the weight of the horse is up to date and accurate, establish what worming strategy will best fit their lifestyle, speak to the owner about how they think their horse would best take a wormer and advise on an appropriate preparation.

References :
1. Abbott, J.B. & Barrett, J. (2008). The problem of diagnosing tapeworm infections in horses, Equine vet. J., 40 (1):5-6.
2. Clayton, H.M. & Duncan, J.L. (1979). The development of immunity to Parascaris equorum infection in the foal, Res Vet Sci., 26(3):383-4
3. Collobert-Laugier, C., Hoste, H., Sevin, C., Dorchies, P. (2002) Prevalence, abundance and site distribution of equine small strongyles in Normandy, France, Vet Parasitol., 110:77–83.
4. Corning. S. (2009). Equine cyathostomins: a review of biology, clinical significance and therapy, Parasit. Vectors, 2(Suppl 2): S1.
5. Mfitilodze. M. & Hutchinson, G. (1990) Prevalence and abundance of equine strongyles (Nematoda: Strongyloidea) in tropical Australia, J Parasitol.76:487–494.
6. Reinemeyer, C.R. (2009). Diagnosis and control of anthelmintic-resistant Parascaris equorum, Parasites and Vectors, 2(Suppl 2):S8


About the author

Blaise Scott-Morris BVSc MRCVS qualified at Bristol in 2011. For three and a half years she worked in small animal practice for both independent and corporate practices, developing a keen interest in client communication and practice profitability. In October 2014, Blaise joined Virbac as a veterinary advisor providing technical support and training, both internally and externally, and participating in pharmacovigilance [monitoring the effects of medical drugs after they have been licensed for use].

AMTRA CPD explained

• AMTRA (the Animal Medicines Training Regulatory Authority) is an independent body whose task it is to ensure that the marketing and distribution of animal medicines in the UK is undertaken in a responsible manner by AMTRA qualified persons.

• AMTRA maintains registers of qualified persons, including Suitably Qualified Persons (SQPs), authorises training centres for course provision, provides information and advice for registered persons, monitors and accredits continuing professional development (CPD) for SQPs and regulates professional conduct.

• SQPs are permitted under the Veterinary Medicines Regulations to prescribe and supply medicines classified as POM-VPS and NFA-VPS.

• For more about AMTRA and becoming an SQP







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