Worming

Common Worms Effecting Horses

Many species of worm that effect horses can live inside a horse, but they can be grouped according to their life cycles, consequences to the horse, and susceptibility to drugs.

Small Strongyles (Redworms)

Small red worms probably pose the greatest threat to a horse’s health.

The adults living freely within the large intestine absorb nutrients from the food that passes them by. In large numbers they will cause weight loss, and possibly diarrhoea, yet don’t often cause a problem. Whereas, the strongyle larvae ingested by the horse from contaminated pasture form cysts in the large intestine wall, and these cysts then rupture to release the young adult causing trauma to the intestinal wall.

During spring/summer cysts rupture out intermittently causing a small amount of repairable damage, yet in the late summer/autumn the cysts form and accumulate as they don’t rupture out until the following Spring when they all rupture simultaneously causing more severe damage to the large intestinal wall, severe diarrhoea and dehydration, and often death.

This condition is known as larval cyathostominosis or larval cyathostomiasis.

The control strategy for larval cyathostominosis is two-fold:

  1. Control the adult population on the pasture – Poo-picking.
  2. Secondly, prevent the formation of encysted larvae in late Summer/Autumn by the use of a wormer that will kill them.

Large Strongyles

Large Strongyles are a particularly nasty type of worm, that fortunately is rarely seen anymore due to their sensitivity to the now commonly used ivermectin wormers. They have form cysts within intestinal blood vessels. This can damage the vessels to the point of cutting off blood supply to large portions of small intestine, with often fatal consequences.

Almost all worming programmes designed to control other worms will also control the large strongyles

Tapeworms

The University of Liverpool has shown that the tapeworm has a considerable role to play in causing certain types of potentially fatal colic.

Eggs layed onto pasture are ingested by mites, the parasite develops inside the mite on the pasture, which is then eaten by the horse and the developing tapeworm is released.

These mites can be found on almost all pasture, and hence almost all hay/haylage. Control must, therefore, be aimed at killing the adults within the horse. This can be reliably achieved by using a wormer effective against tapeworms on an annual basis. A simple blood test is available that gauges a horse’s previous exposure to tapeworm, which can be useful in horses with an unknown worming history, and also in horses with colic.

Pinworm

The equine pinworm is relatively uncommonly seen. The adult lives just inside the rectum of the horse and lays its eggs in a very sticky material that then sticks to the horse’s backside, causing severe itching, the only real consequence of infection, which may lead to weight loss, and destruction of tail hairs. This worm is controlled by worming, and thorough cleansing of areas used by the horse to scratch.

Bots

Stomach bot eggs are laid on the horse’s hair (often on the legs), and then ingested when the horse grooms. The eggs then develop into larvae that attach themselves onto the stomach lining causing small ulcer where they attach, but these do not appear to cause clinical signs. Most worm control strategies will eradicate bots successfully.

Roundworms

The equine roundworm is a large worm that affects mainly youngsters. Natural immunity is normally present by 6 months of age, so after this age it rarely causes a problem. The common signs of infection are poor weight gain, pot belly and colic. Prevention is the best strategy by grazing mares and foals on clean pasture, with regular poo-picking, and appropriate worming of the mare.

Lungworm

Lungworm can affect horses, although the donkey, not the horse is its natural host. Infected horses will not be able to infect other horses, so this is a disease that almost exclusively affects horse that co-graze with donkeys.

Know Your Wormer

Drug name Worms Targeted Products (Trade names)
Ivermectin Large Strongyles
Small Strongyle Adults
Pinworms
Lungworms
Roundworms
Bots
Equimax
Eqvalan
Eqvalan Duo
Eraquell
Maximex
Vectin
Moxidectin Large Strongyles
Small Strongyle Adults
Small Strongyle Larvae
Pinworms
Lungworms
Roundworms
Bots
Equest
Equest Pramox
Pyrantel Large Strongyles
Small Strongyle Adults
Pinworms
Roundworms
Tapeworms (at double dose)
Exodus
Pyratape-P
Strongid-P
Fenbendazole Large Strongyles
Small Strongyle Adults
Pinworms
Roundworms
Tapeworms (at double dose)
Panacur
Fenbendazole (5 days) Large Strongyles
Small Strongyle Adults
Small Strongyle Larvae
Pinworms
Roundworms
Tapeworms (at double dose)
Panacur Guard
Praziquantel Tapeworms Equimax
Eqvalan Duo
Equitape
Equest Pramox

 

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