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20 February 2019   
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 Parasites -
  Strongyles Vulgaris
  Strongyles Equinus
  Strongyles Edentatus
  Parascaris Equorum
    (large roundworm)
  Stomach Bots
    (Oxyuris equi)
    (Oxyuris equi)
 Parasites -
  Black Flies
  Harvest Mite
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Parasites of the Horse

Horses can suffer from a variety of parasites both internal and external. There are more than 150 internal parasites known to infect horses, the five major kinds are: large and small strongyles, ascarids, bots, and pinworms. Internal parasites can cause serious health problems and care should be taken to either use preventative treatment or treat the horse before long term damage to its intestinal structures and other internal organs occurs. It is a year-round job to ensure your horse is safe from parasites If they are not controlled and a horse carries a heavy load of internal parasites it will not be getting enough food value from its daily rations. The infested horse will become unhealthy, the coat will become dull, it will loose condition, it's resistance to disease may be lowered, it will have less energy and be prone to colic, Therefore it is important to adopt a regular worming programme as well as careful management of the horses environment, to keep your horse safe from all internal parasites

There are five major kinds of equine internal parasites: large and small strongyles, ascarids, bots, and threadworms:

Strongyles (bloodworms), Large and Small
The most common and most destructive of all internal equine parasites are the large strongyles. The larvae are swallowed as the horse eats infected grass. They can be seen in horses of all ages, except in very young foals. Strongyles range in length from 1/2 inch to 2 inches.
The eggs can develop into infective larvae on pasture within three days. When they are swallowed, the larvae shed their protective coating, or "sheath", and migrate to different organs of the horse for further development.

Strongylus Vulgaris larvae are particularly dangerous, moving through the horse's arteries to the mesenteric artery ( the main artery feeding the digestive system) For approximately four months these larvae continue to grow in the mesenteric artery, subsequently returning to the large intestine where they burrow into the intestinal cavity. After six to eight months, the worms mature and their eggs are passed through the manure.

Strongylus Equinus larvae migrate to the liver for about six weeks. Afterwards they travel through abdominal organs to the large intestine. After about nine months the adults mature and lay eggs.

Strongylus Edentatus larvae migrate to the liver for about nine weeks. Afterwards they move to the abdominal cavity where they form nodules in the lining and gut wall. Strongylus vulgaris cause severe damage if left untreated. As they migrate up through the artery they roughen the surface of the walls, leaving tracks where blood clots can form. These clots break away from the wall into other blood vessels where they lodge and cause a lack of blood flow to the intestine. The artery walls may become weakened by larval damage, once the walls of the artery are damaged they will be prone to burst, leading to immediate death.

If untreated large strongyles in the large intestine eat away at pieces of flesh causing severe colic, diarrhea, fever and anemia from the bleeding bite wounds.

Strongylus Equinus and Strongylus Edentatus if untreated can cause liver damage.

Parascaris equorum (large roundworms) largest internal parasite to affect the horse. Ascarid larvae are swallowed as your horse eats infected grass, the eggs are passed in manure and become infective larvae. While grazing, the horse swallows the larvae, which hatch and burrow into the walls of the intestine. From there, they are carried by the bloodstream into the liver and lungs. The horse coughs up the larvae and swallows them again. Larvae mature into egg-laying adults in the intestine. The size of the worm varies from 5inches to 15inches long, reaching up to 1/2 inch in diameter when mature, similar in appearance to earth worms.

Common in young horses, not so common in horses over five years old. Immunity may develop following exposure to large roundworms during adolescence, though the dangers of Ascarids are severe if they are left untreated, especially to foals 6 months or younger. In young horses serious infection can build up quickly, lleading to liver and lung damage, poor growth and possible death. Larvae in the bloodstream can cause coughing, fever, pneumonia, bleeding lungs and respiratory infections. Adult stage ascarids live in the small intestine where they can cause blockage, colic, ruptured gut and death.

Bots come in three types: Gastrophilus intestinalis, which is the most common; Gastrophilus haemorrhoidalis, the nose bot; and Gastrophilus nasalis the throat bot:

Stomach Bots - Gastrophilus intestinalis are the larvae of the adult bot fly. The female bot fly willclick to see larger image lay small, yellow, sticky eggs on to the horse where they become attached to the coat, usually around the leg and chest area. As the eggs hatch, an itchy substance is distributed over the skin, encouraging the horse to lick, the lavae then attaches to the horses tongue and is inadvertently injested. The larvae pupate and attach to the mucus lining of the stomach wall where they remain for about nine weeks, until they are passed through the horse's digestive system and expelled into the manure. The larvae burrow into the ground and mature into adult flies at this stage the whole cycle starts again.

If left Untreated: Bots can cause inflammation of the mouth and stomach irritation. Severe infestation can cause intestinal blockage, often leading to irritation, ulcers and colic. Bots are active from spring until the first killing frost in the autumn.

Worming treatment for Bots is more effective once at mid summer and again after the frost. Bot eggs can be removed from the horse's coat with a special bot scraper, or a warm damp cloth, or the coat can be clipped. Horses that are stabled during the summer do not usually suffer from Bots.

Threadworms (Oxyuris equi)
chiefly infect young foals they may be ingested through an infected dam's milk, or through eating infected grass or through skin penetration from infected bedding. Larvae that enter through the skin migrate to the lungs, up to the wind pipe where they are coughed up and swallowed. Larvae mature into adults in the small intestine where they lay eggs that are passed in the manure.
Once penetration has occurred and Threadworms migrate through the lungs and small intestine, they cause damage. Their life cycle is short, two weeks, but during that time foals will be seriously ill. Though foals quickly develop immunity, they can suffer severe diarrhea during the migration period.

If left untreated the Threadworm larvae in the lungs can cause bleeding and respiratory problems. The most severe damage often occurs in untreated young foals who can suffer diarrhea, weakness, weight loss and poor growth.

Pinworms (Oxyuris equi)
Horses become infected with pinworms when they have ingested eggs that have dropped into feed or water. The Pinworm larvae mature in the large intestine by feeding off the intestinal lining. The adult female Pinworms then move to the anal area where they lay eggs covered with a sticky fluid that causes severe itching.

Heavily infected horses may become nervous and refuse food. Severe itching under the tail causes the horse to continuous bouts of rubbing until the tail hairs become matted and break off. Leaving the sore skin open to infection.

The most common external horse parasites are black flies, bot flies - also internal, sucking lice, mites, midges ( a condition commonly known as sweet itch ocurrs when the horse has an allergic reaction to the midge bight, severe cases can render the horse useless) mosquitos and ticks.

Black Flies - Simulium vittatum Zetterstedt
This species is strictly a nuisance attacking horses and cattle, but not humans, though it does fly around people's faces. ) It is a small, dark, stout-bodied fly with a humpbacked appearance. Breeding occurs in polluted areas, stagnant ponds, swamps and sewage areas etc. It is a nuisance by both swarming and biting particularly around the areas without much hair - the inside of the ears. It can draw blood while it feeds and the horse may become infected.

To prevent an attack put horse fly nets with covered ears on the horse while grazing.

A small wingless insects present all year round more noticeable in housed animals. Louse are contagious and infestation spreads when animals are in close contact. Female lice attach their eggs (nits) to the hair fibres, they take about ten days to hatch into nymphs and a further two to three weeks before they develop into adults. It is just possible to see adult lice with the naked eye by carefully parting the coat. They are greyish brown in colour and not much larger than a pinhead. Biting lice are the most common, feeding on debris from the surface of the skin causing intense irritation and crusty scurfy areas that the animal will bite and scratch to alleviate their discomfort. Sucking Lice can cause chronic anaemia and infested animals may suffer weight loss and reduced immunity to disease.

Harvest Mite
Harvest Mite - bracken bugs/harvest bugs - Trombicula autumnalis. The first active stage in the lifecycle of the Harvest Mite is the six-legged larvae which attacks the animal. They are orange/yellow in colour and approximately 0.2mm long and only just visible to the naked eye. The larvae are active during the day, particularly in dry, sunny condition from May until the end of September. They swarm around any warm-blooded animal where there is little or no hair and the skin is quite thin, in the ears and around the nose.

The larvae feeds by thrusting its small hooked fangs into the skin where it injects a fluid to break down the cells under the surface and sucks this liquid feed back into its digestive system. It does this for three or four days over the same site until the lavae has increased in size to be three or four times larger.

The larvae then drop to the ground and burrow into the soil where they remain for about six weeks. They then develop into an eight legged nymph and finally into an adult. Once fully grown the adult Harvest Mite feeds on insects and plants, laying its eggs to start the cycle again.

The fluid injected into the skin can cause a skin reactions in sensitive skinned animals with irritation and discomfort.

Both Lice and Mites can live away from the animal for about three to four months. Bedding, floors, rugs etc should be treated separately to avoid re-infestation.

Tick infestations is more of a problem in uncultivated rough meadows and woodland areas. Adult female ticks lay groups of eggs, which hatch to form a colony of young ticks that attach themselves to grass stems while they wait for a host to pass by. Ticks bury their heads into the animal's skin sucking on the hosts blood until they become large and look similar to a wart. Do no attempt to pull them off, as often the head will come away and stay embedded in the skin, sometimes causing an infection. Specific tick treatment is required.

Some animals may suffer from an allergic reaction to the saliva of the biting midge - a condition known medically as 'Sweet Itch.', or Summer Seasonal Recurrent Dermatitis (SSRD), . Virtually all breeds and types of ponies and breeds can be affected, from Shetland ponies to heavy draught horses, though the condition is rare in the English Thoroughbred. The most commonly affected area is the top of the tail and the mane. In more severe cases the neck, withers, hips, ears and forehead, and in even more chronic cases the mid-line of the belly and the saddle area, the sides of the head, the legs, sheath or udder may also be affected. If a horse has severe Sweet Itch it is classed as an unsoundness, possibly because it effects the area under the saddle, rendering the horse useless for riding. Symptoms include severe pruritus [itching], hair loss, skin thickening and flaky dandruff. Exudative dermatitis (weeping sores), Today there are more remedies available to treat this disorder, see your vet. Keeping the horse stabled will often limit the midge activity.

Flea eggs are usually laid on the floor or bedding and very few on the body of the host. They appear as white specks that hatch when the conditions of temperature and moisture are favourable; around two days in the summer to about12 days. The fully grown larvae spins a cocoon in which the pupa develops and they can stay alive in this cocoon for up to a year before hatching.

Infestation is common in small pets but horses and cattle may occasionally become infected. They cause severe irritation and if untreated they can cause anaemia, particularly in young and debilitated animals. All bedding should be destroyed and all floors and cracks regularly cleaned to stop re-infestation. Regular flea preventative treatment is advised for household animals. Veterinary advice and products are most effective.

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