SMALL redworms are the most common and one of the most dangerous parasites. Small redworms have a very short lifecycle, often as short as five or weeks, however, they reproduce in very large numbers.

Almost all small redworms go through a unique stage in their lifecycle. As larvae they burrow into the gut wall of the large intestine and become encysted. Some of the larvae will develop in the gut wall for a period of time before re-emerging to become an adult, egg laying worm in the large intestine.

Other larvae remain in the gut wall, lying dormant for months or even years. This state is referred to as the inhibited encysted larvae and is where the parasite can become very dangerous to horses. Tens of thousands of encysted larvae can line the large intestine, this impairs the absorption of nutrients, often causing weight loss and illness.

The larvae remain in this state until a ‘mass emergence’ is triggered. This is usually caused by a change in conditions, such as winter to spring. When the ‘mass emergence’ occurs it can cause life-threatening bowel inflammation, known as colitis (larval cyathostominosis).

Small redworms can be up to 2.5cm long and are thin and reddish in colour.

SYMPTOMS

  • Loss of condition and weight
  • Anaemia
  • Distended stomach
  • Dull coat
  • Diarrhoea
  • Colic

    • TREATMENT

    Faecal worm egg counts are usually the most accurate way of diagnosing parasite activity, however, because the small redworm larvae are dormant they will not show up on a faecal worm egg count, making them much more difficult to detect.

    There is currently no possible way of detecting small redworms while they are dormant in the intestine wall, therefore, the only way of making sure your horse does not have any is through an effective worming programme.

    All horses over the age of six months should be wormed against small redworm, owners should worm against the parasite in late autumn or winter. The most important thing is that horses are wormed against it before spring because this is when the ‘mass emergence’ is most likely to occur.

    The two active ingredients licensed to treat encysted small redworm are a single dose of moxidectin or a five-day course of fenbendazole. However, there is increasing evidence to show small redworm resistance to fenbendazole. Moxidectin is considered to be highly effective against adult small redworm including encysted larvae.

    If you are unsure about worming your horse you should contact you veterinary surgeon and come up with an individually tailored worming plan. You should also contact your veterinary surgeon immediately if you suspect that your horse might have small redworm.

    PREVENTION

    Prevention is the best way to deal with small redworm. Keeping all horse pastures clean and removing droppings helps to reduce the chance of horses eating the parasite. In the early stages of the small redworm’s life cycle the eggs hatch into larvae from the horses drug. These larvae then wriggle away and contaminate pasture, especially during wet weather. The larvae can travel as far as three metres.

    Picking up droppings from fields is especially important in the summer months. Mixed grazing with sheep or cattle is another very good way of helping any paddocks from being horse sick.