Every year Veterinary Surgeons from our practice treat many horses affected by worm related problems. The effects of worm larvae migrating through the gut of horses can cause severe weight loss often accompanied by diarrhoea. This disease is known as 'larval Cyathostomiasis'. Irreversible damage can occur within the gut leading to permanent ill thrift, only 50% of badly affected horses make a full recovery. Horses of all ages can be affected but the disease is commonest in horses of less than six years of age.

Because of the severe damage to the intestines that can be caused by worms it is very important that an effective worm control strategy should be carried out.

When considering a worming programme it is necessary to understand a little about the life cycle of the cyathostome (small red worm - gut worm). The adult worms within the gut lay eggs which are deposited on the pasture in faeces, this occurs from early spring until the autumn. (Generally the number of eggs in the droppings decreases during the winter months.) Once on the pasture the eggs remain infectious for up to five months. When eaten by a horse the worm larvae burrow into the gut where many encyst (hibernate), and can remain there for many months or even years. Large numbers of these encysted larvae then emerge from the gut during the spring and summer months, and it is this emergence of larvae which results in the symptoms of larval cyathostomiasis. It is important to note that due to the long grazing season of horses in the U.K. (virtually 12 months) that the disease can occur at any time of year, not just in the spring and summer.

There are two equally effective worm control strategies, which we will call, a) Traditional system, and b) New Liverpool System.

Traditional worming strategy

1. Use one type of wormer for an entire grazing season i.e. 12 months starting in the late autumn.
2. Worm every six weeks, except with EQUEST (13 week interval).
3. Change the wormer to an entirely different one every 12 months. A suitable rotation would be, (a) Equest (b) Strongid - P, (c) Eqvalan.
4. The autumn wormer must be Eqvalan (or Equest) every year to help control Bots.
5. Check faecal egg counts once every 12 months to ensure that the adult worm population is under control (remember encysted larvae do not produce eggs, and cannot be detected clinically).
6. An annual worming with a double dose of Strongid - P will protect against tape worms.

Only two wormers can kill hibernating small red worms. Equest and Panacur guard. All worm programmes should include at least one treatment with one of these per year.

A good traditional worming schedule would be :-

July Equest
Oct Double Strongid P (to kill tapeworms).
Mid Nov. Equest (this will also kill bots.)
March Equest
July Equest.

1. Collect droppings from the pasture twice weekly.
2. Many large studs and stables alternate the grazing of pasture with cattle and sheep.
3. Do not overstock pasture.

New Liverpool System.

Due to concerns about the development of RESISTANCE by small red worms to some of the wormers currently used, clinicians at Liverpool University have devised a system so that the use of anthelmintics (wormers) can be reduced. They point out that under the traditional system many horses are wormed every six weeks even if they have no worm infection. The Liverpool system relies on regularly monitoring the number of eggs in every horse sharing pasture. Liverpool University has developed the Diagnosteq' service to analyse samples and advise when worming becomes necessary.

1. Collect faecal sample every six weeks and submit for worm egg count. (Diagnosteq £7.00 + V.A.T.). If samples are negative the testing interval is extended to three months and in some cases to six months.
2. Do not worm the horses unless 50% of animals have an egg count over 300 eggs/g.
3. Blood sample once yearly to check for tape worms. (Diagnosteq £15.00 +V.A.T.). Can be arranged with annual vaccination.
4. Take a faecal egg count from any new horse coming onto the yard and worm accordingly.

Advantages of the system are:-

1. Fewer wormers are used, this will hopefully delay the development of resistance. This should mean that the existing wormers will be available to treat worm infection.
2. Although the initial set up costs will be higher than the traditional system, eventually there should be a saving on the purchase of wormers.
3. It's a 'green' system. Fewer drugs are administered to the horses.
4. Monitoring of the faecal egg counts gives assurance that the worm control strategy is working.

You can also visit the Liverpool University site www.liverpool.ac.uk for more information.

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