Roundworms (nematodes) are the most important group of internal parasites affecting cattle in Australia and can significantly impact production efficiency.

Roundworms have a direct life cycle, but most require a period on pasture in a non-parasitic form. Roundworms are mostly a problem for cattle under 18 months of age.

The most important roundworms in cattle in Australia are:

Other roundworms found in cattle include:

Most of these worms share the basic roundworm life cycle but some have additional stages inside the cattle.