The nematodes are the endoparasites that cause the most severe economic losses in cattle. In some areas of the world, the liver fluke (a trematode) also causes heavy losses in cattle production.

A knowledge of the complex life cycles of endoparasites contributes to effectiveness of control by permitting development of well-timed control programs. With the exception of avermectin and ivermectin the products currently available for control of endoparasites have some serious limitations.

Descriptions of the economically significant endoparasites of cattle are given in following sections.