Test your knowledge of horse parasites
Internal equine parasites (worms and bots) can seriously affect the health and performance of horses and ponies, so controlling them is an important part of being a responsible owner.
Let’s look at the most important parasites a bit more closely.
Small redworm or cyathostomes are the most common internal parasite in horses. Small in size, they can be big in number and cause serious problems in the large intestine. Larvae can encyst in the gut wall for many months, hibernating over winter undetected, until they emerge all at once in the spring or pre-foaling. They can also emerge at anytime if the horse is stressed. Synchronous re-emergence of larvae, termed ‘larval cyathostominosis,’ can cause severe damage to the intestinal wall leading to diarrhoea and colic, which can cause death. High numbers of adult cyathostomes in the gut can also cause chronic cyathostominosis, seen as weight loss, dull hair coat, pot-belly, loose faeces and colic.
Faecal egg counts do not detect the presence of encysted cyathostomes, as only the adult worms produce eggs. The best way to control this parasite is to drench all horses in the late winter or early spring with a moxidectin-containing product and repeat those at high risk in autumn. High risk horses are those under four years old, noting that one to three year old horses and those grazing heavily contaminated pastures have the highest chance of developing clinical larval cyathostominosis.
Large redworm or large strongyles are rarer but still occasionally cause life-threatening damage, so are still considered dangerous and a good reason to treat all horses with an effective drench at least annually.
Large roundworm or ascarids are the most important parasite affecting foals and young horses. Adult worms are massive and reach 50 cm in length. Large numbers of worms can lead to physical blockages in the gut requiring surgery.
Tapeworms tend to form clusters of adults in the gut and can cause colic. Spring and autumn treatments with a drench containing praziquantel are recommended.
Bots are the larval stages of the bot fly that attach to the inside of the horse’s stomach. Remove any sticky yellow eggs seen on horses’ coats and treat any hidden internal bots when the weather cools, once the irritating bot flies have disappeared.
Pinworms live in the horse’s large intestine and rectum. The female pinworm moves out of the horse to lay eggs on the skin around the anus, causing lots of irritation. This process can be so itchy that horses will rub the site causing broken tail hairs and may rub until there’s hair loss and ulcerated skin.
Lungworm can cause chronic coughing with a nasal discharge and occurs in horses co-grazing with donkeys.
Knowing which parasites to target and using drench strategically, along with faecal egg counts and pasture management, are all increasingly important to avoid drench resistance development.
Ultra-Mox is New Zealand’s only moxidectin 3 in 1 combination wormer and can contribute to a reliable worming strategy. It can help control and treat roundworms including tapeworms and bots.
To develop a drenching programme for your farming operation or to learn more about using Ultra-Mox within a worming programme for your horses, speak with our team in your local PGG Wrightson store.