All sheep are susceptible to internal parasitism, but younger animals ages 2 to 12 months have a higher incidence. This is due to development of a measure of resistance to some species of worms from previous infestations as animals grow older. Since young animals tend to be more likely to carry a worm burden, they also are more likely to be heavy shedders of worm eggs into the environment. For these reasons, preventative measures are important for all sheep and critical for young animals. Life Cycle Parasite life cycles are described as either direct or indirect.
Most sheep parasites have direct life cycles.
The adult parasite with a direct life cycle resides inside the host animal from which eggs are shed into the environment. Ingestion of this immature stage of the parasite allows the life cycle to proceed. An intermediate host, such as an insect, is required for parasites with an indirect life cycle. Examples include the tapeworms, Moniezia , and Thysanosoma . Infective larvae develop inside the intermediate host.