Pastures and internal parasites. You can’t have one without the other. If you have  pastures, your horses will have internal parasites. These pesky little creatures that can erode a horse’s good health have been successful in thwarting the best efforts of science to destroy them completely. Parasites can be controlled, but as long as there are horses, there very likely will be parasites that will attack them.

Unfortunately, one of the internal parasite’s favorite breeding grounds is also the healthiest place for a horse to be when it is not being ridden or involved in a training program–the pasture. One can grasp the magnitude of the problem when it is realized that there are more than 150 types of internal parasites that can afflict horses.

The number one culprit in the parasite world right now is the small strongyle, says Craig Reinemeyer, DVM, PhD, associate professor at the College of Veterinary Medicine at the University of Tennessee.

Ascarids or roundworms primarily are a problem for foals and growing horses. (Photo courtesy Farnam Co.)

“Small strongyles are found universally wherever horses are pastured,” he says. “Virtually all horses on pasture are infected with them. Although severe clinical infection with obvious symptoms that we associate with a ‘wormy’ horse may occur, most horses infected with small strongyles do not display symptoms. It is difficult to document, but subclinical effects still occur