How tough will the battle be?

Most horse owners realise that heavy worm burdens can cause ill thrift. Horses may develop a dull or rough coat, have little energy and lose weight.

However, they can also be responsible for colics, intestinal ruptures, gut irritation, lung problems, damage to internal organs and a host of other maladies.

The biggest troublemakers are large strongyles (bloodworms), small strongyles, ascarids (more commonly called roundworms), pinworms, bots, tapeworms, threadworms and lungworms.

Each has a different lifecycle involving adult and larval stages. A horse can be infected with different kinds of parasites, all at different stages in their life cycles.

Mature parasites will be laying eggs furiously - potentially hundreds of thousands of eggs can be passing out in an infected horse's dung. Often, within a matter of days, if conditions are right, these will be able to infect other horses grazing the pasture.

The prevalence of parasites varies from country to country and region to region, the most likely key influence being climate.

Next, we'll look at the drenches available to us in the battle against equine parasites.

All horse owners need a knowledge of drenches and their effectiveness. Not all drenches work against all parasites and it is the responsibly of horse owners to do their bit in reducing the chances of drench resistance developing.

However, drenching is only part of a worm-management strategy As we'll discover later, how you manage your horses and the pasture they graze will have a major bearing on your ability to keep worm counts in check.

» Next: A is for anthelmintics