There is increasing confusion over the parasites known as small strongyles. In the early years of parasite control, small strongyles were thought to be of little consequence to the health and well-being of the horse. After effectively controlling large strongyles and other common internal parasites in horses, researchers discovered that small strongyles cause much more damage than previously imagined; damage that can lead not only to poor performance, but to death in extreme cases.

We went to career-long parasite re-searcher and American Association of Equine Practioners member of 28 years John Paul, DVM, MS, to ask some basic questions about small strongyles. What we found out will help you understand this complicated world of worms a little better. You should discuss deworming options with your veterinarian; different species of parasites cause problems in different areas of the country, and the world. A practitioner who is taking care of a number of horses in your specific locale is best able to see what is happening, and adapt what he sees to a program for your individual horse.

Q: What are small strongyles?

A: They are a group of parasitic worms living in the cecum and large colon of the horse. There are about 40 species of small strongyles throughout the United States and the world. They belong to a family known as cyatho-stomes, all of which have a similar life cycle.

Small strongyles are the most numerous parasite of horses. If you were to open a normal horse, you would find many more small strongyles than any other parasite–tens of thousands to hundreds of thousands in some cases.

Most horse owners will never see a