The nematodes are the endoparasites that cause the most severe economic losses in horses.

A knowledge of the complex life cycles of endoparasites contributes to effectiveness of control by permitting development of well-timed control programs. Products currently available for control of endoparasites have some serious limitations.

Descriptions of the economically significant endoparasites of horses are given in the following section. Other endoparasites of minor importance or which are restricted to limited geographic areas are listed after the ectoparasites.