It is near impossible to overestimate the potential damage that intestinal parasites do to horses. Prior to development of the modern dewormers of the late 70's you could safely say that horses’ life spans were fairly well limited by that damage, particularly large strongyle larvae migration. The cause of the death did not happen all of a sudden but by damage accumulated over time. Even with modern dewormers, if not used appropriately, we pay for parasites with increase vet bills, increased feed bills and horses that don't look their best. Fortunately most deworming regimens have removed the dangerous large strongyle threat but other less dangerous parasites may be nibbling at your pocketbook daily.

There are two ways parasites hurt our horses:

1. The migrating larvae physically damage the horse's tissue.
2. The adults both physically damage and consume the tissues.

Though most horse owners realize that intestinal worms consume the horse’s tissues, few realize that serious damage is done by the migrating larvae. The migrating larvae can be responsible for

• colic
• diarrhea
• pneumonia in foals
• skin diseases
• paralysis

Older programs were designed to periodically kill off the adults. The aim of a modern parasite control program is to prevent the horse from picking up the larvae, which do much of the damage. Of course by consuming tissues the adults are also responsible for disease including:

• decrease feed efficiency
• weight loss
• colic
• poor quality coat
• diarrhea.

Even if your horse does not have signs of disease, improperly designed deworming programs may have you increasing the amount fed to your horse and may have even turned to expensive supplements just to feed the worms.