The importance of worming
horses
Regular worming is vital for the health and optimal performance of our horses. Avoiding pasture contamination will help to prevent worm-related colic and achieve the main aim of breaking the small redworm re-infection cycle. However, owners often worm their horses for short-term rather than long-term reasons.
Our long-term aim should be to break the life cycle of small redworms by preventing redworm eggs from being passed out to contaminate the pasture. Killing off the adult worms present in the gut achieves part of this goal, however the larval stages of the redworm are also important as they can cause severe health problems for our horses.
Pasture management & tips
Droppings should be removed on a daily basis this is the best way to reduce pasture contamination.
* All horses on the premises should be on the same worming programme and wormed on the same day with the same wormer. New horses should be wormed with a suitable multi wormer and stabled for at least 3 days.
* Try not to overcrowd pastures, ideally graze one horse per 1 acre
* Worm pregnant mares before and after giving birth (seek advice on worming pregnant mares and young foals)
* Where possible mix grazing with cattle or sheep who are unaffected by ingesting equine worms
* Chain harrowing should only be carried out in hot dry conditions this exposes the worm larvae which is then killed by the heat of the sun.
* Rest pastures when ever possible. Worm larvae can live for many years both on pastures and in horses so simply resting a pasture does not guarantee it being worm free.
* Never feed your horses or ponies off of the ground or stable floor and always clean feed buckets and water containers or troths regularly.
Worm types
SMALL REDWORM (cyathostomes)
The small redworm has become our horses biggest parasitic enemy, causing anything from wasting and poor condition to serious life threatening colic and even death. Small redworm are the most common parasite to effect your horse. They are thin and can be up to 2.5cm long, they range in colour from white to red. Small redworm larvae are picked up by horses whilst grazing and can develop into adults within five weeks. In autumn, their development is prolonged and they remain in cysts as tiny inhibited larvae (early L3 larvae) within the gut wall. These are known "encysted larvae" in the late winter or spring, an unknown trigger causes these larvae to emerge in great numbers of 4th stage larvae, the symptons of this can be severe causing damage to the large intestine, resulting in, diarrhoea, weight loss, colic and even death. The encysted stages of redworm can account for over 90% of the total small redworm burden so controlling these larval stages is an important part of your worming programme.
Resistance
Some strains of redworms have become resistant to the benzimidazole wormers (eg. fenbendazole) which means that despite regular worming, horses may still be infested with adult and larval redworms. To check for redworm resistance, collect dung samples for faecal egg count analysis 'before and after' worming. If your horse's redworms have become resistant to your regular wormer, your vet will find a significant worm egg count after worming i.e. more than 200 eggs per gram of dung and you should switch to a new worming product.
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.
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.
Lungworms (Dictyocaulus arnfieldi)
Lungworms are white in colour and are between 6 and 10 cm in length. The lifecycle of lungworms is different to other nematodes as adults settle in the lungs rather than the intestine. Eggs are laid then travel up the trachea, are swallowed and passed out in the faeces. Further development then takes place on the pasture, infective larvae are swallowed by horses or donkeys to further develop into egg laying adults.
It is extremely rare for lungworm larvae to develop to full maturity in horses as the horse is not a good host for that particular parasite. Horses can be infected with lungworm but as they do not mature in to egg laying larvae in any numbers to sustain a population on the pastures. Exceptions to this in horses can arise in very young or old horses and seriously depilated horses whose immune systems are impaired. Up to 70% of donkeys carry lungworms often showing no clinical signs of infestation and it is in donkeys where the parasite reaches full maturity. Donkeys do not always develop the symptomatic cough that is seen in horses but if horses are grazed along side donkeys then particular care must be taken to treat for lungworms accordingly with particular attention to foals as they can sustain permanent lung damage if infected
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
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 traditional thinking was to treat with Ivermectin or Moxidectin based products preferably in December or January as the adult bot flies are killed of by freezing temperatures but as weather patterns are changing leading to milder winters without early frosts it might be advisable to treat twice per year. If treatment is given before the bot flies have stopped egg laying then the larvae will still be capable of causing damage throughout the winter and into spring. If treatment is delayed until after the first frost, then the larval stages burrowing in the horses mouth and stomach, are capable of causing problems. Therefore it is important to use products capable of killing all stages of bots perhaps during summer and autum whilst the flies are still active and then again later in the winter after a true hard frost.
The yearly worming guide below is a guide to worming your horses and ponies. It is not necessary to worm more fequently then every 6 weeks. Always follow the instructions inside each box of wormer. If you are not sure email us at: mail@wormersonline.co.uk and we will be happy to offer you free advice on worming, or consult a qualified person or your vet.
January -
Routine Worming:
use: Noromectin, Eraquell or one of the other suitable Ivermectin based wormers
Febuary -
For Encysted Redworm treat with a five day course of
Panacur or Equest Oral Gel
March -
Routine Worming:
use:Noromectin, Eraquell or one of the other suitable Ivermectin based wormers
April -
Tapeworm Double dose with a Pyrantel based wormer or single dose with Equitape
May -
Routine Worming:
use: Noromectin, Eraquell or one of the other suitable Ivermectin based wormers
June -
Routine Worming:
use: Noromectin, Eraquell or one of the other suitable Ivermectin based wormers
July -
Routine Worming:
use: Noromectin, Eraquell or one of the other suitable Ivermectin based wormers
August -
Routine Worming:
use: Noromectin, Eraquell or one of the other suitable Ivermectin based wormers
September -
Routine Worming:
use: Noromectin, Eraquell or one of the other suitable Ivermectin based wormers
October -
Tapeworm: Double dose with Pyrantel based wormer or single dose with Equitape
November -
For Encysted Redworm treat with a five day course of
Panacur or a single dose of Equest Oral Gel
December -
For Bots use Noromectin, Eraquell or one of the other suitable Ivermectin based wormers after the first frost this will help kill off any Bot larvea