Equine Worming

Worming for horses

Worms can affect all types of horses and ponies whether stabled or at grass. If they are not controlled they can cause weight loss, colic and in severe cases - death.  Increasing numbers of horses are kept on smaller areas and many paddocks are over-grazed which can in itself lead to a serious worm problem - more and more worm eggs are passed out in the droppings on to the pasture, contaminating the pasture, only to be eaten again.

Equine wormers

Wormers are divided into four different chemical groups:

  1. Macrocyctic lactones (Ivermectins and milbemycins), EqvalanEquest, Eraquell, Bimectin, Vectin, and Equimax
  2. Benzimidazoles, Panacur (fenbendazole) Telmin (mebendazole)
  3. Pyrantel Embonates, Strongid P, and Embotape
  4. Praziquantel, Equimax, and Equitape
  • Macrocyctic lactones treat bots, small redworms, large redworms and lungworms.
  • Benzimidazoles treat roundworms, large redworms and small redworms.
  • Pyrantel Embonates treat large roundworms, large redworms, small redworms, seatworms/pinworms and tapeworms (all species).
  • Praziquantels treat all three species of tapeworm
  • NB: only Panacur Equine Guard and Equest are licenced for the treatment of encysted L4 cyathostones (small redworms).

Equine Annual Worming Schedule

  • January - MarchRoutine worming
  • AprilTapeworm
  • May - SeptemberRoutine Worming
  • OctoberTapeworm
  • NovemberEncysted Redworm
  • DecemberBot Worming

This is a general outline for an annual worming schedule.

Average weights.

HandsWeight (Kg)Type
9 - 13 200/250 Donkey
9 - 13 200/250 Shetland
13 - 14 300 Pony
14 - 15 500 Arab/Hack
14 - 15 500 Polo Pony
15 - 16 600 Racehorse
15 - 16 600 Hunter
16.3 - 17 700 Draught

Should you stable your horse during routine worming?

If living Out
Worm your horse with the product suitable for the time of year, leave in same field for 24/36 hours then move your horse on to clean pasture. To help sterilize contaminated pasture harrow when hot and dry, topping also may be effective. If possible remove dung from the fields twice a week.
When Indoors
Leave your horse in one stable for the 48 hours, afterwards remove everything that could be contaminated (bedding, hay etc) then clean the stable and contents with a strong disinfectant. Then replace with fresh bedding and forage and then the horse can go back in. It is good stable management to regularly clean all feed and water buckets.  A good worming programme is always made more effective by good management.
If your horse is returning to the same field then there is no point in keeping him in after worming (he is no more infective just after worming than he was before).
Remember that any change in circumstances and management may upset your horse and in some cases lead to a bout of colic particularly if your horse is used to grass and then suddenly gets stabled so in general situations stabling is not really necessary. It is best that your horse does not associate worming with a sudden change to their life style.
New Arrivals
As a general rule new arrivals on a yard should be treated with the appropriate products (small redworm, redworm and tapeworm treatment) and where possible should then be turned out on to a paddock that is specially reserved for this purpose.

Equine Healthcare and Pasture Management

  • Never feed a horse direct from the stable floor where the environment may be contaminated.
  • Always read the packaging and follow the instructions.
  • Never underdose as this could lead to resistance.
  • Do not over stock pasture which can force animals top graze where the worm count is high.
  • Given enough room to graze horses will develop their own grazing and toilet areas know as lawns and troughs
  • Rest your pastures if possible for six months or so as frost and sun can help kill infected areas.
  • Keep your stable and feeding environment clean and hygienic by using a good disinfectant.
  • If horses are moved to clean pastures worm them 48 hours before the move to prevent the spread of infection.
  • Try to graze young horses away from older horses as the younger horses carry the biggest worm burden and as such are responsible for the majority of pasture contamination.
  • Try to pick droppings up as often as possible twice weekly is ideal but weekly will help.
  • Get friendly with a local farmer and let him graze sheep on your horse paddocks as they are great vacuum cleaners and will not pass worms to your horses.
  • Know the weight of your horse to ensure it gets the correct dose.
  • Moxidectin based Wormers should not be used on foals less than 4 months of age.
  • Moxidectin based Wormers should not be used on severely debilitated horses.
  • Pyrantel Embonate based Wormers should not be used on debilitated horses.
  • When worming give your horse a treat so that he remembers worming in a positive light.
  • Worm all horses that are on the same yard on the same day with the same active ingredient.
  • Worm all newcomers to your yard and stable them for 24 hours before allowing them on the pastures.
  • Keep accurate records of your worming procedures.
  • If you suspect a resistance to benzimidazole based wormers consult your vet and arrange a faecal egg count
If you are in any doubt about your horses health, please consult a vet.

Worms

Nematodes

Large Redworms(Strongylus vulgaris)
Adult Large redworms worms vary in size between 1.5 and 5 cm. Large redworm was once the most important parasite affecting the horse because the migrating larval stage damage the lining of the arteries, particularly those supplying the gut. However in the UK older horses have usually developed immunity due to the efficient use of equine wormers in this country. Large redworm infection is more generally a problem in younger horses. These worms migrate through and damage some of the the body's vital organs. Treat with Equest, Eqvalan, Eraquell, Bimectin, Vectin and Equimax.
Large Roundworms / Ascarids(Parascaris equorum)
Large roundworm also known as ascarids are very long worms up to 40cms when mature and produce large numbers of tough coated adhesive eggs which stick any surrounding environment. They are white in colour. They can stick to the coat and udders of the mare and even to the walls and stable floors. The eggs have very thick shells and therefore can survive on pastures over the winter months. These worms are eventually coughed up by the horse and then renter the body to be re-circulated once more. Treat with Strongid P or Embotape.
Hairworms(Trichostrongylus axei)
Adult hairworms are only about 7cms in length and so are very hard to see with the naked eye.  These worms are usually controlled by products containing Moxidectin or Ivermectin. They are unusual as they are also a parasite of sheep cattle and pigs. As the name suggests they live in the stomach where they feed on blood. The larvae then migrate via the bloodstream to various body tissues and mature on the intestine. Threadworm larvae can penetrate the mammary tissue and be transmitted to young suckling foals via the mothers milk.
Stomach Hairworms(Habronema muscae)
Stomach hairworms are  1-2.5cms in length and are long slender and white in colour. These worms are usually controlled by the worming programmes containing Moxidectin or Ivermectin but are unusual as they are also a parasite of sheep cattle and pigs. They develop into adults in the stomach where they feed on blood.  These worms are transmitted by flies landing on and ingested dung so fly control measures will help to reduce infections. They are also capable of remaining on and damaging the skin and causing "summer soreness".
Pinworms(Oxyuris equi)
Pinworms are not considered harmful but can provoke irritation around the tail. Pinworms inhabit the large and small colon and have a relatively simple life cycle. Female pinworms are up to 10cm long, and white in colour. The females lay their eggs around the anus of the horse using a sticky substance, which is irritating to the horse. The eggs are dislodged as droppings are passed and fall onto the pasture where they are eaten by horses. Treat with Strongid P or Embotape.
Lungworms(Dictyocaulus arnfieldi)
Lungworms are white in colour and are between 6 and 10 cm in length. The adults are only found in donkeys so only horses that share paddocks with donkeys can become infected. Treat with Equest, Eqvalan, Eraquell, Bimectin, Vectin and Equimax.
Small Redworm(Cyathostomes)
Small redworm (small strongles/cyathostomes) are the most common parasite to effect your horse. They are up to 2.5cm long, thin and can range in colour from white to red.  Small redworm larvae are picked up by horses whilst grazing. Historically, the key period of risk was spring and summer. However, recent climatic changes have led to hot, dry summers, and warm, wet autumns and winters. Spring and autumn have now become the periods of greatest risk. Furthermore, recent studies that have involved monitoring pasture infectivity; have shown high levels of infective larvae present on turnout paddocks, even in January after snow. This means that “winter worming” is now just as important as worming during the summer grazing season. Small redworm larvae can develop into adults within a period of five weeks. In the autumn, however, their development is prolonged and they remain in cysts as tiny inhibited larvae (early L3 larvae) or as larger late 3rd and 4th stage larvae within the gut wall. These are broadly termed “encysted larvae” but in the late winter or spring, an unknown trigger causes these larvae to resume their development. The symptoms of simultaneous emergence of large numbers of 4th-stage larvae are colic, weight loss, diarrhoea and can cause devastating damage to the large intestine, sometimes resulting in death. Even before they emerge, large numbers of encysted larvae can cause fatal disease. The encysted larvae stages can account for over 90% of the total small redworm burden so controlling these larval stages is an important part of any equine worm control programme.  Horses particularly at risk are those that have grazed on heavily stocked and contaminated pasture, have not been regularly wormed regularly or have mixed with other horses that have not been treated regularly and the risk increases for horses under 6 years old.
Horses that are subject to effective worming procedures and where good pasture management is practised through out the year will pass fewer small redworm eggs in their droppings so the levels of worm burden will be less and therefore the risk of encysted larvae will be reduced. However these worms have a life cycle of between 6 weeks and up to 2 years so caution must be exercised even when pastures have been rested.
It is possible for horses with an early EL3 infestation to appear healthy and well. Furthermore, if a Faecal Egg Count (FEC) test is carried out on an EL3-infected horse, the small redworm burden may not appear to be high because it is mainly present in the dormant EL3 form.
Only 2 anthelmintics have claims of efficacy against encysted small redworms they are:
Panacur Equine Guard/Fenbendazole (5 day course)
Equest/Moxidectin (single dose)
Symptoms:
Diarrhoea, rapid and severe weight loss, colic and can even KILL your horses. As cyathostomes attach themselves to the gut and are absorbed into it they reduce the efficacy of the gut wall to absorb essential nutrients which can lead to general ill thrift in the horse and an incapability to utilise properly a balanced diet.

CESTODES

Tapeworm(Anoplocephala perfoliata, Anoplocephala magna & Anoplocephaloides mamillana)
Tapeworms are an important and potentially very damaging parasite affecting the horse. They preferentially attach themselves to the junction of the small and large intestine the ileocaecal junction. Here, they can cause bowel irritation, intussusception (where one part of the intestine telescopes into another), rupture, or twisting of the intestine.  It is thought that tapeworm may be responsible for up to 20% of surgical colics. Tapeworms are present, to a greater or lesser extent, in the majority of horses.  Parts of the country with acidic soils (for example, heath land), which favour the survival of the intermediate host of the tapeworm (the forage or oribatid mite), tend to have the highest level of infection.  Recent studies have shown that far from being a seasonal problem, tapeworm infection occurs all year round. This is because the forage mite not only lives on pasture, but also survives perfectly well in hay and on bedding, For this reason, six- monthly dosing (at double the standard dose for Pyrantel based products) is an essential port of any worming programme.
Appearance:
Tapeworms in horses are generally much shorter than dog or cat worms, they are flat, triangular and relatively short being approximately  8 cm long by about 1.5 cm wide. However the equine tapeworm grow up to 20cm long, white in colour. Rarer species can be up to 80cm long. They live in huge numbers attached to the gut wall at a natural narrowing of the gut (the ileocaecal junction).
Symptoms:
Can cause colic, sometimes fatal, by blocking blood vessels. Current research estimates that over 20% of cases of spasmodic colic are related to tapeworm burden. Treat with Equitape, Embotape, Equimax or Strongid P.

ARTHROPODS

Bots(Gasterophilus)
Bots are not actually worms as they are in fact flies. Bots are an internal parasite of the horse as part of their lifecycle involves internal development. The fly lays it's eggs on the abdomen, legs and throat of the grazing horses in late summer.  When they are then licked off by the horse the larvae are stimulated and the larvae hatch and burrow into the lining of the gums. They migrate to the stomach after about one month which becomes inflamed and ulcerated and eventually (some 10 months later) are passed out in the dung. Bot eggs can be seen on the horses coat during summer and early autumn and can be removed with special bot knives or bot scraping blocks. The entire population of Bots reside in the stomach over winter so that is why it is important to treat with Ivermectin or Moxidectin based products preferably in December or January as the adult bot flies are killed of by freezing temperatures.

Written specially for Nutrecare