Zoetis is warning owners that they could be under-dosing.
This in turn can cause worms to develop resistance to wormers and impact on how infestations are managed in the future.
One case study found a 13.1hh Connemara weighed 60kg more than the owners expected.
Another showed that a full tube of wormer would not be enough to treat one competition-fit 16.3hh warmblood involved in the study.
The company warned that resistance to wormers is a growing problem
Resistance happens when parasites are no longer susceptible to a drug used to control them.
These then multiply and, if the process continues, only resistant worms remain.
Wendy Talbot, Zoetis vet, advised that horses should be weighed at least once a year using a weighbridge.
“Our case studies give a very real perspective on how easy it is to under-estimate the weight of our horses,” she said.
“Weigh tapes, although less accurate [than weighbridges], are a great way to keep tabs on weight once you have the accuracy of the weighbridge weight to refer to and have factored in any discrepancies.
“Remember that many horses will change in weight throughout the year.”
She added some feed manufactures offer a portable weighbridge service.
Knowing the current weight of the horses that you wish to treat before purchasing your wormers can help your vet or SQP to ensure that you buy the correct dose in each case.
While horses can have large tapeworm burdens and appear healthy on the outside, the worms can cause problems so testing horses for tapeworm and treating them where necessary is good horse husbandry.
Unlike other worms in the horse, tapeworms develop inside an intermediate host — the microscopic forage mite. Horses become infected when they eat hay or grass containing mites, which are themselves infected with tapeworm larvae. These then develop into adult tapeworms inside the horse’s intestines.
Testing for tapeworms in horses
Testing for tapeworms cannot be done through the standard faecal worm egg count (FWEC). Either a blood test or the relevatively new saliva test can be used to identify whether your horse has a tapeworm burden in its gut.
A blood sample can be taken by your vet to test for infection, a method known as the ELISA or tapeworm antibody test. A horse with a high level of tapeworm infection will produce a large number of antibodies, which can be detected in the blood.
The test indicates a broad level of intensity, rather than tapeworm numbers. The amount of antibodies will indicate whether the burden is low, medium or high.
While the blood test is useful for assessing whether your horse has been infected with tapeworms in the past, it is not a reliable indicator of response to treatment. This is because it takes around four to five months for the antibody levels to return to normal after the worms have been killed. Therefore the test only needs to be carried out once a year.
The saliva test — EquiSal Tapeworm — has been developed by scientists at Austin Davis Biologics at the company’s laboratory in Northamptonshire. A horse’s saliva is taken by its owner using a specially developed swab, and then sent off to the laboratory for analysis.
Horses with evidence of a high tapeworm burden are likely to be susceptible to infection with tapeworms in the future. They should be treated a second time that year, before being retested 12 months later.
Treating a horse for tapeworm
There are two different approaches to tackling tapeworm. Treatment can be targeted, following a blood or saliva test, or administered within an annual worming programme.
Targeted treatment can reduce the likelihood of worms becoming resistant to treatment and identifies horses at risk of high levels of worm infection.
Using this method, horses are tested for tapeworms once a year. Those with a high burden are treated after the test and then again six months later. The test is then repeated the following year to find out how successful treatment has been.
New horses on the yard should have a tapeworm test and a FWEC, or be treated for both tapeworms and roundworms, before they are turned out with others.
In some yards, targeted worming may not be suitable nor practical. In these instances, it is best to treat for tapeworms every six months.
Tapeworm infection is not strongly linked to seasonality, so the time of year that treatment takes place is not particularly important. As risk is higher after prolonged periods of grazing, however, it seems wise to treat at the end of a summer out at grass.
It is important to be aware that not all wormers kill tapeworms. These particular parasites can be treated with one of two drugs — praziquantel and pyrantel. The latter must be used at a double dose.
Fortunately, both drugs are very effective and cause death and detachment of the tapeworms from the gut wall within 24-48hr following treatment. They are available as single products or in combination with other drugs that target different types of worms.
Parasite populations on the pasture can be reduced by regular removal of droppings, resting grazing and rotating sheep and cattle on to horse fields.
To conclude then, careful pasture management combined with correct testing and treatment will ensure that tapeworm infection is controlled.
With October just around the corner and the nights drawing in, there is no denying that autumn is on its way. Make sure you and your horse are ready for the colder weather with our seasonal horsecare guide.
1. Hardcore
Putting hardcore down in gateways before the winter will help these areas stay compact, and prevent them from becoming too muddy and slippery.
2. Winter rugs
If you didn’t get your winter rugs cleaned and repaired in the spring, now is the time to do it. Or if you need new rugs, it’s time to go shopping! Take a look at the latest rugs on the market.
3. Clippers
Get your clippers serviced and the blades sharpened by a specialist so you are ready to tackle those winter woolies. If you want to learn how to clip like the experts, check out our clipping masterclass video.
4. Worming
Autumn is the ideal time to test and treat horses for tapeworm, while vets recommend all horses should be wormed for encysted small redworm during November/December. So now is the time to get organised and order your worming supplies, checking that the active ingredients are the right ones for the the types of worms you are targetting.
Encysted small redworm: are you risking your horse’s health?
Encysted small redworm within the gut wall: each red dot represents a cyst
ALL horses should be wormed for encysted small redworm during November/December, even if they have a negative faecal worm egg count.1,2 Nonetheless this year’s National Equine Health Survey showed almost one in three of us are getting it wrong, leaving our horses at serious risk from these lethal parasites.3
Small redworm are the most common worms found in UK horses and, in their encysted stage, they are potentially fatal. The problem is that they won’t show up in a faecal worm egg count and they may not cause any obvious symptoms so you probably won’t know your horse has got them.
There are only two active ingredients licensed to treat encysted small redworm: a single dose of moxidectin or a five-day course of fenbendazole. Resistance to fenbendazole is now widespread in the UK so a resistance test is recommended before using it.2
Don’t risk your horse’s health. Speak to your vet or SQP about responsible worm control.
Visit www.esrw.co.uk to find out more about encysted small redworm.
1. Nielsen (2012) Veterinary Paristology. 185. 32-44
2. Matthews, JB (2008) Equine Vet. Educ. 552-560
3. The National Equine Health Survey, conducted by the Blue Cross and supported by Zoetis, was completed by 4951 horse owners in May 2015, with records returned for 14,952 horses. The survey contained questions on general horse health, care and management and was validated by Professor Josh Slater of the Royal Veterinary College.
5. Bedding
Choose bedding wisely if your horse is to be stabled in the coming colder months. If your horse suffers from respiratory problems consider using a dust-free bedding combined with rubber matting. You may find you can save yourself money by buying in bulk.
6. Dietary changes
If your horse is overweight the next few months is the ideal time to slim him down, or if he is inclined to lose weight now is the time to start thinking about his autumn/winter feeding regime before any weight loss occurs. Remember that good quality forage is important before turning to cereal feeds. Feeding oil will also help maintain condition.
7. Mud fever
Mud fever can start in autumn if conditions are wet and muddy. Avoid long periods of exposure to these conditions, as bacteria from the soil can enter the horse’s body through damaged skin or cuts.
8. Vaccinations
Check if your horse’s vaccinations are due. It’s easy to allow them to slip and costly if you have to restart the full course. Consult your vet if you are unsure what vaccinations your horse needs.
9. Teeth
Get your vet or equine dental technician to check your horse’s teeth before winter, to ensure they are able to make the most of their feed. This is particularly important for youngsters and older horses.
10. Grass Laminitis is most commonly associated with spring grass, but cool nights lead to an increased accumulation of sugars in grass. If you own a laminitis-prone horse consider whether you need to restrict their grass intake.
11. Fly gear
Clean your fly sheets and masks and store them ready for use in the spring. Bring all your fly sprays, shampoos and other liquids indoors to prevent freezing and thawing, which may make them less effective.
12. ‘Winterise’ your yard
After the ground has frozen you won’t be able to sink new fence posts, so make sure they are all secure now. Check gutters and downpipes are in good condition and clear of debris. Insulate your pipes and unhook hoses when not in use, especially during the night when it may drop below freezing.
13. Cooling
If your horse works up a sweat while being ridden, have a wool or fleece cooler to hand to throw over him while he’s cooling down to prevent him from becoming chilled.
14. Shooting
If you live in an area where deer stalking or shooting may occur, it is best to avoid riding out at peak times. Outfit yourself and your horse in bright colours or talk to your fellow riders to make sure you can be seen and heard.
Horse owners could be risking their horse’s health by not worming correctly.
Results from this year’s National Equine Health Survey (NEHS) showed that 29% of people who thought they had treated for encysted small redworm had used an unsuitable product.
Small redworm are the most common worms found in UK horses and, in their encysted stage, are potentially fatal.
They don’t show up in faecal worm egg counts and may not cause obvious symptoms so owners may not know their horse has them.
The only two active ingredients licensed to treat the small redworm are a single dose of moxidectin or a five-day course of fenbendazole.
The survey results showed 22.5% of those who specified how they treated for encysted small redworm had used ivermectin and 6.3% had used products licensed for tapeworm.
Of the remaining respondents 64% (down from 71% in 2014) had correctly used moxidectin and 7% had used fenbendazole.
“Encysted small redworm are potentially the most harmful parasites to affect horses in the UK, yet the survey results show consistent confusion over the correct product to use to minimise risk.
“It is imperative for owners to discuss their worm control plan with their vet or SQP and use the right product at the right time to safeguard their horses’ health,” said Wendy Talbot, for equine health company Zoetis.
The company recommends horses should be wormed for encysted small redworm during November or December. This can be combined with a treatment for bots.
Owners should also carry out faecal worm egg counts every two-three months throughout the grazing season and treat for strongyles as required.
Recent news about the re-emergence of pinworm as a parasitic problem has prompted a flurry of stories from owners who’ve spotted these unwelcome visitors around their horses’ hindquarters.
“They seem to be this year’s must-have accessory for the discerning equine,” says Leila Mitcham, who first suspected infestation when she noticed some uncharacteristic tail swishing by her thoroughbred gelding, Beau. “I’ve been involved with horses for more than 30 years, but have never come across a case of pinworm.”
Leila’s three horses mainly live out on 4.5 acres of grazing that is poo-picked daily. Each is wormed for encysted redworm and tapeworm and has a regular faecal egg count, so it surprised Leila to discover that pinworms were in effect living “under the radar”.
The pinworms flourished unnoticed because their eggs are laid around the anus area and not expelled in dung, and are therefore not detected in faecal egg counts.
Upon closer inspection, Leila noticed telltale yellow dots under Beau’s tail — pinworm eggs. She then spotted an adult female worm emerging from his anus.
“Beau was the only one to show any signs,” she says.
This lack of visible evidence is another reason why pinworms tend to be overlooked. Perianal pruritis (itching of the tail) can be a giveaway, but clinical signs may appear in only a small percentage of horses.
And while young horses have been considered most at risk, this is no longer so.
“There are numerous reports of clinical signs in mature adult and geriatric horses,” says Edd Knowles MRCVS, adding that a much broader age range is now thought to be vulnerable.
Pinworm presence in Leila’s horses — two thoroughbreds aged 22 and a five-year-old cob — would seem to confirm this.
A persistent problem
How worried should we be about these low-profile parasites?
Aside from the discomfort caused by itching, possible tail-wrecking and consequential behavioural changes, a sizeable burden can apparently cause more serious problems.
“Pinworm have also been blamed for causing some types of colic by causing inflammation of the colon and caecum,” warns Edd.
Leila’s horses are now undergoing a treatment programme aimed at eradicating the internal worm burden. But Edd says that pinworm are showing resistance to some wormers.
“The continued presence or rapid reappearance of eggs despite repeated treatment was found in mature horses in Germany,” he says. “Egg shedding ceased only after subsequent mebendazole treatment. In the US and New Zealand, adult pinworms that had survived treatment with ivermectin/abamectin were killed only by pyrantel or oxfendazole.
“If you do suspect pinworm, consult your vet to put together a thorough treatment plan,” Edd advises. “If signs persist following treatment, a different class of wormer may be necessary.”
Pinworm is a re-emerging disease and all horses are at increased risk of infection — that was the message conveyed by Edd Knowles when speaking at the British Equine Veterinary Association (BEVA)’s congress in September.
Previous veterinary thinking was that Oxyuris equi — more commonly known as pinworm — affected only a limited age range of young horses, it caused mild clinical signs and was easy to control with a routine worming programme.
However, recent reports suggest this is not the case.
“Anthelmintic [wormer] resistance is emerging,” said Mr Knowles. “Many reports involve mature adult horses that have received apparently appropriate recent anthelmintic treatment.”
Adult pinworms are white and up to 15cm in length, and primarily live in a horse’s right dorsal colon.
Female pinworms lay yellow eggs around the horse’s anus — often leading to perianal pruritus (itching of the tail) — and then die, leading to the worm being passed in droppings. Dislodged pinworm eggs become infectious within three to five days.
Signs have also been reported to persist after initial treatment with an ivermectin or moxidectin wormer.
“The continued presence or rapid reappearance of eggs despite repeated treatment was found in mature horses in Germany. Egg shedding ceased only after mebendazole treatment,” Mr Knowles added.
“In the US and New Zealand, adult pinworms that had survived treatment with ivermectin or abamectin were killed only by pyrantel or oxfendazole.”
Always consult your vet when pinworm is suspected.
“I currently use three doses of pyrantel embonate or mebendazole at two- to three-week intervals in persistent, severely affected cases,” Mr Knowles told H&H.
Reports of resistance and re-emergence in the worm world mean that targeted treatment is more important than ever. Cara Hallowell-Evans MRCVS debunks some of the myths of modern worm control
Severe infestation with Parascaris equorum (roundworm), which inhabits the small intestine, leads to intestinal obstructions and is known as parascariosis. Mature horses rarely show signs, but it can be fatal in foals
Myth one
Using ivermectin in spring will keep small redworm under control.
Fact
Confusion sometimes surrounds the significance of cyathostomins (also known as small redworm or strongyles), a group of parasites affecting almost all grazing horses. It is the immature larvae of the small redworm that causes disease, rather than the adult worms.
Larvae are the juvenile stage of gut worms. The larvae go through
a period of development within the wall of the intestine to enlarge and shed their outer sheath within the gut wall.
Horses become infected by ingesting infective larvae, which have developed on pasture from eggs passed in faeces. The warmer the weather, the faster the larvae develop to the infective stage.
Larvae embed themselves (become encysted) within the wall of the intestine, where they develop. This development can be arrested within the wall for months or even years, however, and we still don’t know the precise factors that trigger subsequent reactivation.
Clinical disease, termed larval cyathostomosis, ensues when large numbers of larvae emerge and cause damage to the interior intestine wall. This results from the accumulation of large burdens of larvae in the mucosal lining and is common in youngstock, or as a consequence of poor management in adult horses.
Treating a horse with ivermectin during spring is a known risk factor for this simultaneous emergence — possibly due to the decimation of the adult population that encourages larvae to emerge
and “fill the gap”.
Larval cyathostomosis is most common in spring, although it can occur at any time. Signs include worms in the faeces, severe diarrhoea and oedema (pouches of fluid under the abdomen and jaw).
Sadly, severe cases have a survival rate of just 50%.
Myth two
Large redworm rarely cause a major problem.
Fact
Large redworm can also cause serious disease. As with small strongyles, eggs passed in the faeces develop into infective larvae on pasture and are ingested by the grazing horse. Clinical disease occurs when even small numbers of large redworm larvae migrate to major abdominal blood vessels, causing clots and obstruction that can lead to severe colic.
Large redworm infection is uncommon in the UK in well-managed horses, due to decades of intensive worming. A single annual dose of moxidectin is thought to prevent establishment of infection on farms, but it is important to be vigilant to ensure this parasite does not re-emerge as the reduced use of worm-control drugs is encouraged.
A cyathostomin, or small redworm: this parasite — here at the infective larval stage which would be ingested by the horse from pasture — affects almost all grazing horses and is most common in spring
Myth three
Regular treatment is better than diagnostic-based treatment.
Fact
One of the most important and frequently overlooked facts about worm egg counts is that there is little relationship between the eggs counted and the number of adult worms present. So what’s the point in performing the test?
Egg counts are really useful to identify and target treatment to those horses excreting large numbers of eggs onto pasture — the ones who are therefore contributing most to parasite transmission.
Targeting treatments in spring and summer aims to reduce pasture contamination, decreasing the chance of ingestion of large numbers of larvae and lessening risk of disease. As a method of worm control, targeting is both cost-effective and sustainable.
In addition, it is impossible to identify horses with heavy infection by eye. The only way to establish the presence of parasitic infection is with diagnostic testing, which is more effective for “wormy” poor doers than repeated treatment.
Myth four
A negative tapeworm test means a horse is free from infection.
Fact
Awareness of the impact that high tapeworm burdens can have on equine health is now better than ever, yet testing for these parasites can be challenging.
Tapeworm transmission takes place when segments of the mature worm containing eggs break off sporadically, passing onto pasture in faeces. These eggs are then consumed by a forage mite, which is ingested and digested by the horse.
An infective tapeworm is then released into the gut, where it attaches itself at the junction of the ileum (the end of the small intestine) and caecum (a pouch at the beginning of the large intestine). This causes irritation and potentially colic.
While faecal testing for tapeworm is available, intermittent egg release means that results cannot be taken at face value. A positive result gives a definite indication of active infection, because eggs aren’t possible without the presence of adult parasites. Negative results can never be relied upon to indicate freedom from infection, however, as testing relies on egg packets being shed into the examined portion of faeces.
The ELISA method, which examines equine blood or saliva for antibodies produced in response to tapeworm infection, can be used for individuals but is best used for co-grazing horses to examine herd infection and transmission levels. Interpretation is challenging and it is important to consider that antibodies may persist for months after clearance of tapeworms by treatment.
If test results are moderate or high, it indicates that biannual treatment in spring and autumn is needed. Annual treatment is often sufficient where results are low or negative, but biannual testing is still recommended to ensure control measures are effective.
Although worm egg counts do not predict how many adult worms will emerge, they are a useful tool for identifying and targeting treatment to those horses contaminating pasture
Myth five
Picking up droppings is a waste of time.
Fact
Good pasture management involves regular dung removal and does make a huge difference to parasite burdens.
Traditional methods such as harrowing and rain washing (letting heavy downpours do the job) and even the more modern paddock sweeper, have been shown to be less useful control methods as they distribute larvae all over the pasture.
Methods that remove, rather than spread, manure, by hand or vacuum, are more effective. Weekly removal will prevent dispersal of dung, and therefore larvae, by rainfall or insects. Additional measures such as clipping rough patches to remove protective larval habitats, or grazing sheep/cattle after horses, can help.
A research project is aiming to improve the control of the most common equine tapeworm by finding out more about its intermediate host, the oribatid mite.
The Royal Veterinary College (RVC) and Austin Davis Biologics will monitor three yards infected with tapeworms, each with 20 horses, over an 18-month period after receiving funding from Petplan Charitable Trust.
The project is titled: “Improved control of the equine tapeworm, anoplocephala, through new insights into the biology of the oribatid mite intermediate host”.
Routine sampling of pastures will enable the mite populations to be monitored. Horse saliva will also be tested to monitor tapeworm infection in the horses grazing the paddocks.
“Infected horses pass tapeworm eggs in their faeces that are ingested by oribatid mites, an essential part of the tapeworm’s life cycle, that are found on the pasture,” said the RVC’s Professor Mark Fox.
“Larval tapeworms develop inside the mites within eight to 20 weeks, after which they can infect grazing horses. Despite methods available for the detection of anoplocephala infections in horses, we still know little about the biology of the parasite’s larval stages in these mites or of seasonal patterns of transmission to horses at pasture.”
The study aims to determine the effect of seasonal changes on mite populations, investigate the impact that dung removal has on tapeworm control and examine the effect of deworming treatments.
“The project seeks to develop more effective parasite control programmes which, together with paddock management recommendations, will ultimately result in a reduction in deworming treatments required,” said Dr Corrine Austin, who set up Austin Davis Biologics in 2009 with her father Professor Paul Davis.
Dr Austin said the company’s EquiSal Tapeworm testing will be used to “understand further the complex balance between the tapeworm, its hosts — the horse and oribatid mite, and its environment”.
The research gets underway in the next few months, with the findings being analysed at RVC’s Hawkshead campus near Hatfield.
Sighing with relief at no longer having to wrestle with muddy heavyweight turnouts, you can send those off to be cleaned and proofed ready for next year and get your lightweights out instead. If you haven’t done it already, these will also need to be checked for tears, mended, cleaned and proofed. Now’s a good time to wash your lightweight stable rugs, summer sheets, fleeces and coolers ready for the season, too. Better get on with it.
2. Out with the old, in with the new
If your horse has spent those long winter nights in his stable trying to destroy his haynets and buckets (well, everyone needs a hobby) then chuck out the ones that are completely beyond repair. While you’re at it, why not get the puncture repair kit out and sort out that flat wheelbarrow tyre, re-attach the broom head with gaffer tape so it doesn’t fall off every time you sweep the yard, and replace the fork-head that lost a prong every time there was a frost? If you’re feeling brave, you could even try to persuade your yard-mates to club together with you to buy new ones.
3. Get your saddle checked
Your horse may well have changed shape over winter, and with the competition season looming, it’s a good idea to get your saddle checked to ensure he’s comfortable and ready for the task ahead. Now would be a good time to get his teeth and back checked, too.
4. Spring-clean those stables
With your horse out more, you can finally blitz the stable he’s been living in all winter. Remove any rubber matting and give it a good scrub, and hose the stable down with a pressure washer together with a good disinfectant — make sure it’s animal friendly, non-toxic and safe to use with rubber matting (if necessary.) Safe4disinfectant is used by vets and has DEFRA approval (www.safe4disinfectant.com), or you could try Fieldguard’s Green Gloop, which is harmless to animals and environmentally friendly.
5. Get your fields summer-ready
Consider chain-harrowing your pasture to remove any dead grass, even poached areas, and allow the soil to be aerated. According to Cotswolds Grass Seeds’ pasture management calendar, March/April is also the time to decide whether your paddocks could benefit from over-seeding or re-seeding, and to apply fertiliser (slow-release is best as too much nitrogen can cause high levels of protein in the grass, which is not ideal for laminitic horses.) Visit www.cotswoldseeds.com for more information. The BHS recommends rolling to flatten any poached areas in spring, and taking action against weeds and poisonous plants. Download their PDF on pasture management from www.bhs.org.uk.
6. Test for tapeworm
If you follow an interval worming programme (the administration of specific anthelmintic treatments at set intervals throughout the year), then March is the time to dose for tapeworm and other routine worms. Due to the problem of increased wormer resistance among horses, the BHS guidelines on worming now recommend targeted strategic dosing based on worm egg counts instead of interval worming, with worm (faecal) egg counts being performed every eight-10 weeks. However, as the guidelines point out: “Tapeworms are not detected by routine worm egg counts, so a tapeworm test (either through blood or saliva) should be carried out in spring and autumn.” Download their PDF on worm control from www.bhs.org.uk for more information.
It’s a chore that should be tackled regularly but is easily forgotten, so add it to your horsey spring-cleaning list. Google it, and you’ll find various suggestions online for keeping your horse’s water trough clean and fresh. These suggestions range from adding cider vinegar to goldfish (yes, really!), but your safest and best solution for a clean trough is good old fashioned elbow grease. Drain the water out, get a stiff scrubbing brush, and scrub the algae and scum out of the trough before refilling it. Obviously, don’t use bleach or any toxic cleaning agents. Your horse will thank you for it.
Owners could have a “new tool” in the battle against encysted redworm, thanks to the Moredun Research Institute.
Scientists currently working on a “novel” diagnostic blood test for assessing small strongyle larvae burdens – which cannot be detected at present – are now in collaboration with Austin Davis Biologics to develop the test further.
The initial process detects antibodies in infected horses and it is hoped this will also be possible using saliva samples.
A spokesman for the project said this would “simplify the collection process for horse owners, allowing them to take samples directly from their horses for analysis”.
Group leader Professor Jacqui Matthews, who is developing the diagnostic blood test at Moredun, added: “We are delighted to collaborate with Austin Davis Biologics to further develop this test; the company has significant experience in the development of saliva-based tests for the equine market.”
Small strongyles are a group of parasites commonly found in the guts of grazing horses. In general, the higher the worm burden, the higher the risk of clinical disease in the horse.
The larval stage of the worms plays a significant role in the “disease syndromes” but there is no direct method of detecting the immature stages, as the larvae burrow into the gut wall where they lie dormant, which prevents specific diagnosis and treatment.
They can then mature and emerge en masse in spring, causing diarrhoea and colic, with a mortality rate of up to 50%.
In the early stages of the project, the scientists are working with equine vets to collect samples of blood and saliva, which the aim of comparing saliva test results with validated results from the blood.
Dr Corrine Austin of Austin Davis Biologics said: “We are very pleased to be working with Moredun on this exciting new project. A saliva test for encysted cyathostomins will provide horse owners, equine veterinarians and animal medicines advisors with a new tool to target the treatment of cyathostomin infections in horses.”
Small redworms in horses are from the parasite group cyathostomins and they are the most deadly of all the parasitic worms that live in horses. An increasing resistance to medicinal wormers for horses is helping this deadly group to flourish.
Almost all grazing horses become infected with cyathostomins at some stage in their lives, with most showing no ill effects whatsoever. The infective larvae are acquired slowly over the entire grazing season and migrate into the lining of the large intestine, where they enter a state of arrested development.
The severe damage caused by this type of parasite infection occurs when the arrested stages of this parasite all reactivate at the same time and emerge from the gut lining into the intestine in bulk. This typically occurs in spring, but it’s not entirely clear what environmental factors trigger the reactivation of the small redworm larve.
The huge migration of the small redworm larvae from the lining of the large intestine causes massive disruption to the gut’s ability to function as normal. Many horses with larval cyathostominosis (springtime diarrhoea caused by small redworms) will develop severe diarrhoea. They will also lose weight and become weak. A small proportion of affected horses do not show diarrhoea, but will lose weight and become very dull and depressed.
Larval cyathostominosis can be fatal in up to 50% of cases, even in animals treated intensively. Treatment of this condition is difficult and dangerous. It involves treating the emerging parasite larvae with worming drugs while simultaneously decreasing the inflammatory reaction that is disrupting the normal function of the intestine. Severely ill horses may also need supportive treatment, such as intravenous fluids and protein supplementation. Treatment can worsen the signs of this disease and, ultimately, can lead to death.
For this reason is it vital that horse owners take action to control the presence of small redworm in their horses to avoid the risk of larval cyathostominosis.
Practical steps to control small redworms in horses
Worm all horses in late autumn or early winter: use a wormer that is effective against encysted larvae parasites in the gut wall (such as one containing moxidectin).
Follow a strategic worming programme: faecal worm egg count analysis should be carried out in the spring and summer, leaving individuals with negative or low faecal worm egg counts untreated to encourage non-resistant worms.
Integrate wormer therapy with good grazing management: maintain low stocking densities, rotate grazing with other animal species if possible and pick up droppings several times a week.
Ensure wormer dosages are given as recommended by the manufacturer: weigh the horse or use a well-calibrated girth tape.
Avoid using the same class of wormer year after year.
Rick Farr B.Sc (Hons), B.V.Sc, MRCVS of Farr & Pursey Equine Veterinary Services gives his expert advice on worming your horse
Q: “Worming — how often do you worm your horse? Do you do it twice or four times per year? And what fundamentals should I know and bear in mind when it comes to worming?”
A: Worming is one of those subjects that everyone is always unsure of, however still manage to almost ‘muddle through’.
In my opinion, there are just a few items to remember when it comes to worming your horse:
There is no one single treatment protocol that fits all horses.
It is important to monitor the levels of parasite burden and treat accordingly.
Environmental contamination / burden of parasites should not be underestimated and pasture management is paramount in worm control.
Roundworms and tapeworms are treated very differently.
The very young and very old should be wormed more regularly.
So in answer to your question, how often should you worm your horse? If you are like me you were probably taught years ago to worm every 6-12 weeks. This can still be true in some circumstances, however the vast majority of our equine population should not be wormed this frequently. It is more important to ascertain whether you horse needs worming in the first place. Regular worm egg counts are necessary during the grazing season, which can be between March and September (weather dependent). Horses with single high worm egg counts, regular elevated counts or susceptible horses (very young or old) do then need treating. It is also important to remember that worm egg counts will only show you if your horse has a burden of roundworms, not tapeworms.
So what is a high count? Within our practice we class counts above 250 eggs per gram of faeces as above normal and therefore requiring treatment. With numbers over 500 we then give additional advice with regards to treatment as it is likely that the use of a wormer may cause anything from diarrhoea to colic symptoms.
So you have found out whether your horse needs worming – but when do you treat? Once again, monitoring the worm egg count will tell you how often during the grazing season but, if the counts remain high, rotating the wormer drug class every six weeks may be necessary to get parasite populations under control.
Tapeworms are slightly different. Again, there are accurate ways of finding out whether your horse has a burden and I would advocate having either a blood test or saliva test done to check the levels of parasite burden. However, we still recommend that tapeworm treatment is done twice a year, in spring (March/April) and autumn (September/October).
Also all horses should be treated for encysted redworm, which at the moment cannot be tested for, typically around December. Make sure you choose a wormer that is effective against encysted redworm as not all wormers are.
There are also a few fundamentals you need to consider when it comes to worming:
We do not have any new wormers on the market, therefore over use or unnecessary worming results in resistance to the drugs. We already have a significant amount of resistance to all of the drug classes. Drug use should be strategic and part of a controlled management program.
There is usually only a small proportion of a herd which has a parasite burden. This small number reinfects the rest of the herd. If you identify these individuals through worm egg counts it is much easier to control parasites; this way the whole herd benefits.
High parasite burdens can cause weight loss, colic, performance issues and even death, parasite monitoring and strategic control can save you money in the long run.
Your vet will be able to give you a tailored worming protocol for your yard; get in touch with your local practice and get the advice you need to keep your horse healthy and also save you money!
The body of an emaciated horse has been found “dumped like rubbish” by the side of the road.
The piebald colt was found dead next to Lower Stock Road in West Hanningfield on Saturday (7 January) in an “extremely poor” condition with rope tied around his neck.
A witness said they saw a white pick-up truck pull up and leave the body there around 5.30pm.
The RSPCA is now appealing for information.
“It is difficult to know for sure how this horse died, but he was in a terrible state and would definitely have suffered before he died,” said RSPCA inspector Kate Fletcher.
“The horse was very young, probably just a year old, was suffering from diarrhoea, and emaciated. He looked as if he had had redworm and not been treated for it.
“The rope was likely put round his neck to drag him so he could be dumped like rubbish by the side of this road.
“We urge anyone with any information about how the horse died and how the body came to be dumped in this way to call us.
“Sadly it is not uncommon for horses to suffer from redworm at this time of year. This is easily treated, but if they are not they go downhill very quickly. We would like to remind all horse owners to de-worm their animals at this time of year.”
Anyone with any information should call the RSPCA on 0300 1234 8018.
Worming horses is an important part of every horse owner’s basic horse care routine. Internal parasites which are cause for concern include small strongyles (small redworms), large strongyles (large redworm), tapeworms, roundworms, pinworm and encysted small redworm.
Encysted small redworm are particular worrying. The larval stage of the small redworm bury into the lining of the gut, where they lie dormant. They can then develop and emerge en masse from the gut wall in the early spring, causing diarrhoea and colic, with a mortality rate of up to 50%.
It is not currently possible to test for encysted small redworm, although a new saliva test is under developement, so it is recommended that all horses are treated to remove these in late autumn or early winter to remove the associated risk. All other worming should be undertaken only when tests show a horse is carrying a specific worm burden.
“Don’t be afraid to ask for help” was the take-home message from equine internal medicine specialist Dr Wendy Talbot at the British Horse Society’s (BHS) welfare conference this week (20-21 September).
Parasite resistance and ongoing research mean advice around worming has changed a lot in recent years.
“I think something that is quite misunderstood is how serious this problem can be and how tricky it can be to sort out the right worming control programme for your horse,” said Dr Talbot.
“You certainly should not be afraid to ask what the most up-to-date advice is.”
During her presentation, Dr Talbot showed what can happen to any horse who is left with severe untreated worm burdens — or when parasites are treated too late.
This includes colic, weight loss and in severe cases, a ruptured gut and ultimately death.
Larval cyathostominosis, the emergence of encysted small redworm en masse from the gut lining, is fatal in 50% of cases.
Faecal worm egg counts cannot give an indication of whether a horse is suffering from encysted small redworm, so horses need to be treated for this in late autumn or early winter regardless. The presence of tapeworm also cannot be detected in faecal egg counts, although vets do offer blood and saliva tests.
Dr Talbot stressed pasture management as the “most important” preventative measure in avoiding horses building up major worm burdens.
“Get out there and pick up the droppings, ideally every day, but if not, twice weekly will still help,” she said.
A new video has been created to alert owners to the potential fatal effects of encysted small redworm.
The animation explains the life cycle of the small redworm, and the life-threatening damage it can do to horses.
The parasite is ingested during grazing, then larvae survive in autumn and winter by burrowing into the walls of the intestine. Here they form cysts and their development pauses as they “hibernate” over the winter.
Up to 90% of the small redworm in any horse could be these encysted parasites.
In spring, the larvae can erupt from their dormant state, to carry on their development, in large numbers. This causes damage to the walls of the intestine, which can lead to diarrhoea, weight loss and colic.
This condition, known as larval cyathostominosis, is fatal in up to 50% of cases. Any horse can be affected, with those under six particularly at risk.
Vet Wendy Talbot, of animal health company Zoetis which created the video, said: “Many horse owners may believe they know all they need to about worming but research shows a lack of understanding about the danger posed by encysted small redworm.
Horse & Hound turns mythbuster on the topic of worms and worming by bringing you the facts about some popular
“Unfortunately, once the horse shows symptoms of larval cyathostominosis it is a very difficult condition to treat effectively. The intention of our new video is to help owners get to grips with why encysted small redworm can cause serious harm to their horses and how important it is to take steps to prevent it by speaking to their vet or SQP [suitably qualified person] about worm control.”
Faecal worm egg counts will not detect encysted small redworm as the larvae do not produce eggs. Horses may be carrying several million of the encysted larvae and yet have a negative or low count.
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Acquiring a horse who has clearly had a setback in care — with the aim of restoring him to full health — can be hazardous.
Often, it cannot easily be determined why the horse has fallen into his present state and whether those issues can be fully remedied. If a horse is found to be thin and debilitated at a veterinary pre-purchase examination (PPE), the largely external nature of this examination, taken with the often unreliable dietary and veterinary history supplied by the owner, can place the examining vet in a difficult position when advising the client as to whether or not he will recover.
Certainly, if you are thinking of buying such a horse, a PPE is highly desirable. This will include a detailed inspection of the horse’s teeth, and maybe also a blood test to investigate any debilitating illnesses that might be present.
If you do decide to take on a horse with an unknown history, or a youngster who arrives looking less than a picture of health, a good first question would be: “Is he wormy?”
Although parasites, principally redworms, are an important cause of debility in adult horses, determining whether they are responsible for failure to thrive in an individual case can be difficult. Contrary to a widely held belief, there is no correlation between the faecal worm egg count (often erroneously called a “worm count”) and the number of worms in the horse. Horses with high egg counts may be healthy, but are an important source of infection for other horses. Conversely, those with a large burden of encysted redworm larvae may have low counts or even be completely negative. Tapeworm will often also go undetected.
Horses who are persistently thin are often described as “worm damaged”. There is actually no evidence that even a severe parasitic colitis (an inflammation of the colon lining), if the horse survives it, causes any irreparable damage. With good aftercare and correct nutrition, an affected horse can make a full recovery.
If no information on the horse’s worming history is available, the likelihood of the presence of a heavy burden may have to be inferred from his background — perhaps he has come from heavily stocked premises, for example, with overgrazing and poor management.
Treatment, based on veterinary advice, may be needed. However, it must be administered with care in the winter if there is a chance that the horse is heavily infected with encysted redworm larvae. The sudden killing of these parasites might provoke an adverse reaction.
It may be prudent for the horse to receive anti-inflammatory medication at the same time as being treated with moxidectin, the wormer of choice in this situation. Although a five-day course of fenbendazole is marketed for the treatment of encysted redworms, resistance to this 40-year-old drug is now widespread — and the inflammatory response, if it does work, is greater than with moxidectin.
A possible redworm burden must be treated with care to avoid a potential adverse reaction
Back to basics
Lice are common in malnourished, debilitated horses during winter and spring, unless the horse has been clipped. Itching of the neck, chest and buttocks is a giveaway sign.
The eggs, called nits, look like hayseeds but are attached to the hair shafts. Adult lice may also be seen if the hair is carefully parted, especially if this is done immediately after a rug is removed. Topical treatment should be given on veterinary advice, as some of the lice treatments sold in tack shops and feed stores are ineffective.
Overgrown, neglected feet must be corrected by trimming. Severe overgrowth should be removed in two or more stages, each around two weeks apart. The aim is to correct any excess growth, rebalance the foot to centralise the load into the centre, reduce any misshapen areas known as flares and address hoof cracks. A poorly shod horse may require repeated sessions with a skilled farrier over an extended period before his feet regain satisfactory function.
The horse should be observed eating hay prior to purchase, as if he has any difficulty in doing so that is significant. A full dental examination is mandatory at the PPE and allows a prognosis to be given. Sharp enamel points alone do not generally cause weight loss, unless accompanied by quidding (dropping unchewed feed) or abnormal salivation. It is often thought that “a good rasping” will improve a horse’s body condition, but this is rarely the case.
Soft or cowpat-style droppings should be regarded with suspicion in a thin horse. If dietary causes can be excluded, essentially eating either rich grass or soft, wet, low-fibre haylage, there may be an underlying inflammatory bowel problem which might prove difficult to resolve.
consult with your vet about an appropriate worming programme
Building condition
Assuming that all other health issues have been dealt with, it should be possible to put weight on a malnourished horse in around four to six weeks. Plenty of good summer grass, or the best- quality hay (soft, green and leafy) or haylage, fed ad-lib, should be the cornerstone of the new diet.
Any substantial increase in hard feed levels must be implemented gradually and carefully to gain maximum nutritional benefit without causing additional problems.
In order to keep the meal size small, at least three, or preferably four, feeds should be given over a 24-hour period.
It is logical not to ride the horse during his recovery, as some of the extra calories and protein provided will be diverted to provide the “fuel” for movement rather than rebuilding his body condition.
There is sometimes a reluctance to feed a horse adequately as there is a concern that this will make him more difficult to ride — although evidence that diet truly affects a horse’s temperament under saddle consult with your vet about an appropriate worming programme is almost entirely anecdotal. If this is a consideration, increased calories and protein can be provided by feeding high-calorie, fibre-based feeds, such as oil- fortified alfalfa combined with a feed balancer.
The horse’s body condition score should gradually improve, but this can be subjective and sometimes disheartening. Monthly weighing with a weight tape will allow his progress to be monitored more objectively. If there is no significant improvement in six weeks, seek further advice from your vet. In the majority of cases, there is no reason why a thin horse cannot be restored to a healthy state provided common heath issues are addressed. However, inevitably, a few of these horses are found upon further investigation to have persistent or unmanageable illnesses — and turn out to be a bad buy.
Case study
When the gamble pays off: annie Warren’s Missy arrived from Ireland in poor condition, but appropriate care allowed the pair to enjoy a season’s hunting six months later
Annie Warren bought five- year-old mare Missy unseen from a dealer in Ireland last spring.
“I wanted a horse to produce and bring on,” says Annie. “Missy looked great in the photos and videos I saw, but when she came off the lorry I was a bit shocked. She had travelled badly and was noticeably thin and tucked up.
“I had little by way of health history to work with, so I organised a veterinary assessment,” she adds. “Her hooves were good but quite long, so I had those properly trimmed. A week later she developed a bad respiratory infection and extensive ringworm. I was quite worried about her.”
After considerable veterinary input and a whole summer on good grass, Missy was finally restored to full health.
“I wasn’t really happy with her condition until the autumn,” says Annie, who hunted her successfully all winter. “By then she had put on weight and looked much better. I was so relieved that there were no long-term problems. Missy proved to me that with the right advice and feeding, you can make a huge difference to a horse who has had a bad start.”
A research project is aiming to improve the control of the most common equine tapeworm by finding out more about its intermediate host, the oribatid mite.
The Royal Veterinary College (RVC) and Austin Davis Biologics will monitor three yards infected with tapeworms, each with 20 horses, over an 18-month period after receiving funding from Petplan Charitable Trust.
The project is titled: “Improved control of the equine tapeworm, anoplocephala, through new insights into the biology of the oribatid mite intermediate host”.
Routine sampling of pastures will enable the mite populations to be monitored. Horse saliva will also be tested to monitor tapeworm infection in the horses grazing the paddocks.
“Infected horses pass tapeworm eggs in their faeces that are ingested by oribatid mites, an essential part of the tapeworm’s life cycle, that are found on the pasture,” said the RVC’s Professor Mark Fox.
“Larval tapeworms develop inside the mites within eight to 20 weeks, after which they can infect grazing horses. Despite methods available for the detection of anoplocephala infections in horses, we still know little about the biology of the parasite’s larval stages in these mites or of seasonal patterns of transmission to horses at pasture.”
The study aims to determine the effect of seasonal changes on mite populations, investigate the impact that dung removal has on tapeworm control and examine the effect of deworming treatments.
“The project seeks to develop more effective parasite control programmes which, together with paddock management recommendations, will ultimately result in a reduction in deworming treatments required,” said Dr Corrine Austin, who set up Austin Davis Biologics in 2009 with her father Professor Paul Davis.
Dr Austin said the company’s EquiSal Tapeworm testing will be used to “understand further the complex balance between the tapeworm, its hosts — the horse and oribatid mite, and its environment”.
The research gets underway in the next few months, with the findings being analysed at RVC’s Hawkshead campus near Hatfield.
Sighing with relief at no longer having to wrestle with muddy heavyweight turnouts, you can send those off to be cleaned and proofed ready for next year and get your lightweights out instead. If you haven’t done it already, these will also need to be checked for tears, mended, cleaned and proofed. Now’s a good time to wash your lightweight stable rugs, summer sheets, fleeces and coolers ready for the season, too. Better get on with it.
2. Out with the old, in with the new
If your horse has spent those long winter nights in his stable trying to destroy his haynets and buckets (well, everyone needs a hobby) then chuck out the ones that are completely beyond repair. While you’re at it, why not get the puncture repair kit out and sort out that flat wheelbarrow tyre, re-attach the broom head with gaffer tape so it doesn’t fall off every time you sweep the yard, and replace the fork-head that lost a prong every time there was a frost? If you’re feeling brave, you could even try to persuade your yard-mates to club together with you to buy new ones.
3. Get your saddle checked
Your horse may well have changed shape over winter, and with the competition season looming, it’s a good idea to get your saddle checked to ensure he’s comfortable and ready for the task ahead. Now would be a good time to get his teeth and back checked, too.
4. Spring-clean those stables
With your horse out more, you can finally blitz the stable he’s been living in all winter. Remove any rubber matting and give it a good scrub, and hose the stable down with a pressure washer together with a good disinfectant — make sure it’s animal friendly, non-toxic and safe to use with rubber matting (if necessary.) Safe4disinfectant is used by vets and has DEFRA approval (www.safe4disinfectant.com), or you could try Fieldguard’s Green Gloop, which is harmless to animals and environmentally friendly.
5. Get your fields summer-ready
Consider chain-harrowing your pasture to remove any dead grass, even poached areas, and allow the soil to be aerated. According to Cotswolds Grass Seeds’ pasture management calendar, March/April is also the time to decide whether your paddocks could benefit from over-seeding or re-seeding, and to apply fertiliser (slow-release is best as too much nitrogen can cause high levels of protein in the grass, which is not ideal for laminitic horses.) Visit www.cotswoldseeds.com for more information. The BHS recommends rolling to flatten any poached areas in spring, and taking action against weeds and poisonous plants. Download their PDF on pasture management from www.bhs.org.uk.
6. Test for tapeworm
If you follow an interval worming programme (the administration of specific anthelmintic treatments at set intervals throughout the year), then March is the time to dose for tapeworm and other routine worms. Due to the problem of increased wormer resistance among horses, the BHS guidelines on worming now recommend targeted strategic dosing based on worm egg counts instead of interval worming, with worm (faecal) egg counts being performed every eight-10 weeks. However, as the guidelines point out: “Tapeworms are not detected by routine worm egg counts, so a tapeworm test (either through blood or saliva) should be carried out in spring and autumn.” Download their PDF on worm control from www.bhs.org.uk for more information.
It’s a chore that should be tackled regularly but is easily forgotten, so add it to your horsey spring-cleaning list. Google it, and you’ll find various suggestions online for keeping your horse’s water trough clean and fresh. These suggestions range from adding cider vinegar to goldfish (yes, really!), but your safest and best solution for a clean trough is good old fashioned elbow grease. Drain the water out, get a stiff scrubbing brush, and scrub the algae and scum out of the trough before refilling it. Obviously, don’t use bleach or any toxic cleaning agents. Your horse will thank you for it.
Owners could have a “new tool” in the battle against encysted redworm, thanks to the Moredun Research Institute.
Scientists currently working on a “novel” diagnostic blood test for assessing small strongyle larvae burdens – which cannot be detected at present – are now in collaboration with Austin Davis Biologics to develop the test further.
The initial process detects antibodies in infected horses and it is hoped this will also be possible using saliva samples.
A spokesman for the project said this would “simplify the collection process for horse owners, allowing them to take samples directly from their horses for analysis”.
Group leader Professor Jacqui Matthews, who is developing the diagnostic blood test at Moredun, added: “We are delighted to collaborate with Austin Davis Biologics to further develop this test; the company has significant experience in the development of saliva-based tests for the equine market.”
Small strongyles are a group of parasites commonly found in the guts of grazing horses. In general, the higher the worm burden, the higher the risk of clinical disease in the horse.
The larval stage of the worms plays a significant role in the “disease syndromes” but there is no direct method of detecting the immature stages, as the larvae burrow into the gut wall where they lie dormant, which prevents specific diagnosis and treatment.
They can then mature and emerge en masse in spring, causing diarrhoea and colic, with a mortality rate of up to 50%.
In the early stages of the project, the scientists are working with equine vets to collect samples of blood and saliva, which the aim of comparing saliva test results with validated results from the blood.
Dr Corrine Austin of Austin Davis Biologics said: “We are very pleased to be working with Moredun on this exciting new project. A saliva test for encysted cyathostomins will provide horse owners, equine veterinarians and animal medicines advisors with a new tool to target the treatment of cyathostomin infections in horses.”
Small redworms in horses are from the parasite group cyathostomins and they are the most deadly of all the parasitic worms that live in horses. An increasing resistance to medicinal wormers for horses is helping this deadly group to flourish.
Almost all grazing horses become infected with cyathostomins at some stage in their lives, with most showing no ill effects whatsoever. The infective larvae are acquired slowly over the entire grazing season and migrate into the lining of the large intestine, where they enter a state of arrested development.
The severe damage caused by this type of parasite infection occurs when the arrested stages of this parasite all reactivate at the same time and emerge from the gut lining into the intestine in bulk. This typically occurs in spring, but it’s not entirely clear what environmental factors trigger the reactivation of the small redworm larve.
The huge migration of the small redworm larvae from the lining of the large intestine causes massive disruption to the gut’s ability to function as normal. Many horses with larval cyathostominosis (springtime diarrhoea caused by small redworms) will develop severe diarrhoea. They will also lose weight and become weak. A small proportion of affected horses do not show diarrhoea, but will lose weight and become very dull and depressed.
Larval cyathostominosis can be fatal in up to 50% of cases, even in animals treated intensively. Treatment of this condition is difficult and dangerous. It involves treating the emerging parasite larvae with worming drugs while simultaneously decreasing the inflammatory reaction that is disrupting the normal function of the intestine. Severely ill horses may also need supportive treatment, such as intravenous fluids and protein supplementation. Treatment can worsen the signs of this disease and, ultimately, can lead to death.
For this reason is it vital that horse owners take action to control the presence of small redworm in their horses to avoid the risk of larval cyathostominosis.
Practical steps to control small redworms in horses
Worm all horses in late autumn or early winter: use a wormer that is effective against encysted larvae parasites in the gut wall (such as one containing moxidectin).
Follow a strategic worming programme: faecal worm egg count analysis should be carried out in the spring and summer, leaving individuals with negative or low faecal worm egg counts untreated to encourage non-resistant worms.
Integrate wormer therapy with good grazing management: maintain low stocking densities, rotate grazing with other animal species if possible and pick up droppings several times a week.
Ensure wormer dosages are given as recommended by the manufacturer: weigh the horse or use a well-calibrated girth tape.
Avoid using the same class of wormer year after year.
