While effective, such chemotherapy isn't a magic bullet. That's because even a treated animal can reacquire the parasite by grazing on infected pasture, necessitating yet another round of treatment. To avoid this costly cycle, farmers must be diligent about where and when they put their animals out to graze. Sheep are especially vulnerable to barberpole worm assaults. For one, sheep aren't averse to grazing pasture where manure is present that may contain parasite eggs, according to Virginia Cooperative Extension scientists in Blacksburg.
Sheep also graze plants close to their roots, where parasite larvae are most concentrated.
Once ingested, parasite larvae quickly find their way into the host's abomasum, or true stomach. There, they mature, mate, and produce eggs in about 21 days. In susceptible or young animals, parasite numbers can build so high that the animal loses more blood than its body can replace. Severe blood loss can kill an animal, says Fetterer. Milder or chronic infections can cause lethargy and loss of appetite and can interfere with weight gain.