Expert advice from TIM WESTERN of Drove Veterinary Hospital.

I have recently received several questions regarding equine worming, so - rather than answer specific questions this month - I thought I would give a more general view of internal parasite control practised in horses.

Worms can cause a variety of health problems which include colic, weight loss and diarrhoea.

Worm damage can prove fatal.

The types of parasites which can cause problems are roundworms bots and tape worm.

The encysted larval stage of the small redworm is the harmful stage of the most common parasite to affect horses today.

Control of parasites depends on several different approaches.

These are: l Strategic use of wormers l Pasture management l Removal of bot fly eggs from horse's coat There are a bewildering number of worming products available from many sources, including veterinary surgeons, farmers' shops, trade magazines and the internet.

Only one of these sources is available to give the best independent advice, based on knowledge of your horse's specific situation and on knowledge of the products that are available.

This source is your veterinary surgeon!

In reality, the number of different types of chemicals used is only four, and even these four only cover certain groups of parasites.

There are many different combinations of wormers that may be used for an effective worm control plan, so there is not a right and wrong strategy.

However, some wormers do have a resistance problem, which means we do not normally recommend their use.

One of the most common simple worming programmes involves only four doses of wormer per year to control all major horse internal parasites.

You should consult your veterinary surgeon for details.

The choice of product and when to give it are not the only factors to consider.

It is important to dose accurately for the weight of your horse. Weigh tapes give a reasonable guide to the weight of your horse.

Another factor to consider is that if worm egg counts are performed regularly, it may be possible to reduce the number of wormer doses given in one year.

This reduction of doses also depends on good pasture management.

Pasture management consists of: l Allowing 1.5 acres per horse (in a livery yard you may not be able to do this) l Pick up droppings at least twice per week l Practise mixed grazing with sheep and cattle - these species will consume horse worm eggs and larvae that do not then develop into egg-laying adults, which reduces pasture contamination.

You should also manage all horses kept on the same pasture in the same way - that is, worm them all at the same time, with the same product.

It is also advisable to worm all new arrivals and keep them off the pasture for 24 hours. Again, seek advice from your veterinary surgeon about which product to use.

You should also remember that as horses get older, they do develop some resistance to worm infestations and so may need worming less frequently.

Young horses carry the highest parasite burdens and therefore need the most care over parasite control.

For further advice and information about worm egg counts, please contact us.