Horse Worms and Worming

All horses have varying levels of worm infestation, controlling the worm burden is key to maintaining a healthy horse. Horses left unwormed in contaminated pasture suffer severe often life threatening health problems. Regular worming along with sensible measures to control contamination of pasture is the only way to control the worm problem.

Small Red Worms - Small Strongyles (Cyathastomes)

The most common horse worm with over 40 species worldwide. Red worms have become the main cause for concern due to their ability to develop resistance to modern chemical wormers. The red worms inhabit the large intestine. The life cycle starts with the female red worm laying eggs which pass out in the dung on to pasture, the small red worm larvae feed on bacteria, moult and become infective small red worm larvae contaminating pasture. These small red worm larvae are swallowed by the horse when grazing, thus completing the life cycle.

The small red worm larvae burrow into the gut wall. At the end of winter they re-emerge as adult small red worms. However, some larvae hibernate in the gut wall becoming encysted, they can lay dormant for up to 2 years, these inhibited red worm larvae are resistant to many types of wormer. When they do emerge in large numbers from their hibernation, the adult red worms can cause damage by rupturing the gut wall. Signs of of small red worm infestation include; weight loss, poor appetite, watery diarrhoea, colic, pot belly, stark coat. Small red worms are becoming increasingly resistant to the Benzimidazole group of wormers.

Large Red Worms - Strongylus vulgaris, Strongylus edentatus, Strongylus equinus (Strongyles)

They are referred to as Blood Worms due to their colour and their habit of feeding on blood. Large red worms follow the same life cycle pattern as the small red worms. The large redworm larvae mature in the gut, they feed by burrowing into the arteries suppyling the bowel. The large red worm larvae often cause obstruction to the blood vessels supplying the bowel. Horses with heavy large red worm infestations lose weight, become anaemic and suffer bouts of severe colic.

Large Round Worms - Ascaris equorum

They resemble large white earth worms, they are named round worms due to the shape of their round eggs. Their life cycle is not simple, the adult round worms live in the small intestine, female round worms lay eggs, which pass out in the dung, the infective round worm larvae develop on pasture, the round worm larvae are grazed and swallowed, then burrow through the intestinal wall into the blood vessels. The blood stream carries them to the liver, heart and lungs. From the lungs they travel up the windpipe to the throat and are swallowed. The worm larvae then pass through the stomach to the intestine maturing into adult round worms in about 12 weeks.

The white round worm is a prolific layer of microscopic size eggs up to 200,000 in a day! Young foals are particularly susceptible to infestation on contaminated pastures. Heavy burdens of round worms can result in general unthriftiness, lung damage, anaemia, coughing and occcasionally rupture of the gut. The round worm eggs are becoming resistant to many chemical wormers.

Thread Worms - Strongyloides westeri

Thread like fine worms that are found in the intestines of foals. Foals become infected by thread worm larvae excreted in the mare's milk. The thread worm larvae develop rapidly maturing in 10 days then passing out eggs onto pasture to re-infect the foal. Poor growth, diarrhoea and weight loss are all signs of thread worm infestation.

Pin Worms - Oxyuris equii

A common parasite worm picked up from contaminated hay or pasture. The pin worm larvae mature in the large intestine in 3 to 4 months. The female pin worm lays masses of yellowish grey gelatinous eggs round the anus. This causes severe itching. Horses rub their tails bald and hindquarters raw trying to remove the itch.

Lung Worms - Dictyocaulus arnfield

Donkeys are host to lungworms Dictyocaulus arnfield. Up to 70% of donkeys carry lungworms often showing no clinical signs of infestation. Lungworm can over winter in pasture unaffected by low temperatures. Grazing horses ingest infective larvae that migrate to the lungs via the lymphatic system, and the pulmonary arterial blood supply. Larvae travel from the alveoli to the bronchi and bronchioles where they mature. The eggs are coughed up then swallowed and expelled in the faeces. Once a pasture has been contaminated with lungworm, they emerge every summer. Many horses who are hypersensitive to dust from hay and straw have suffered lung damage as foals. Foals are particularly susceptible to this pest with long lasting lung damage.

Tape Worms - Anoplocephala perfoliata and Anoplocephala magna (Cestodes)

These are flat white worms often called flat worms. Two types are found in the horse, Anoplocephala perfoliata and Anoplocephala magna. Anoplocephala perfoliata is the most common equine tape worm. These tapeworms (A.perfoliata) are fluke shaped, and grow to adults 3cms to 8cms in length. They live at the junction of the small and large bowel in the horse. Horses become infected with tapeworms through eating forage mites which are found in pasture, hay and straw. The tapeworm cycle begins with forage mites eating the tapeworm eggs from the horse faeces. Three to five months after the horse eats the mites the tapeworms being fully mature shed segments containing eggs which are then passed out in the manure. These segments then break up and release tapeworm eggs which the mites devour, and the cycle continues. This tape worm causes irritation, inflammation and ulceration of the gut.

A recent UK research study by Proudman et al. (1998) found a strong association between ileal impaction colic and tapeworm infection. Within this study 81% of ileal impaction colic cases and 22% of spasmodic colic cases were found to be tapeworm related.

ELISA Tapeworm Test

The ELISA Tapeworm blood test will determine whether your horse is likely to be infected with tapeworms. This test measures the level of antibody to a specific tapeworm antigen. Horses with significant tapeworm burdens have elevated levels of antibody. The level of antibody gives an indication of tapeworm infection intensity. About fifty per cent of all horses are infected, at any one time.

Faecal Egg Counts

Faecal egg worm counts are very helpful when determining the worm burden of your horse and helping you plan your horse's worming program. The worm egg counts cover all horse worms except Tapeworms. To check the level of tapeworm infestation in your horse you will need to ask your veterinary surgeon to do an ELISA (Tapeworm) Antibody blood test.

Which Wormer to Use?

Most horse owners worm their horse at least twice a year, and on well managed pasture significant worm burdens are not a problem. The choice of wormer is often made on the basis of advertising or cost and no real follow up is taken to determine whether the wormer was successful, the owner trusts the product was effective. Very often the wormer used, is one to which the worms have become resistant. This has been a real problem in the Southern States of America, Australia and South Africa with land becoming unusable for livestock and horses. In Britain, there is already significant worm resistance to certain classes of chemical wormers. Therefore, it is important to not only worm your horse but to follow this up with a faecal egg worm count test and an ELISA blood test, at least once a year. It is also a good idea to vary the type of wormer used, alternating with herbal parasite repellant products to prevent the worms on your land rapidly building up resistance to chemical wormers.

Zilch Verm

A blend of traditional herbs added to the feed to maintain the overall health of coat and gut whilst repelling unwanted internal parasites. Added to the feed over 5 consecutive days. 1 litre is sufficient for an average sized (500kgs) horse for 2 parasite repel programs 4 to 8 weeks apart. One litre will cover 8 to 16 weeks for one average sized horse.

N.B. Not suitable for pregnant/lactating mares or foals under 6 months old.

Contains: Extracts of traditional vermicide & demulcent herbs. One litre self dispensing bottle

Free Faecal Worm Count Kit & Moon Calendar is included and full directions on using Zilch Verm

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