Delaying anthelmintic resistant parasite development on sheep farms

摘要

Grazing sheep are naturally exposed to gastrointestinal nematodes (GIN). A large number of different GIN species can infect sheep, but they are generally broken into two groups which can be distinguished on the basis of egg morphology: i) Nematodirusor ii) Strongyle worm species. Nematodirus has a different life cycle to most other GIN; Nematodirus eggs require a prolonged period of cold weather followed by a period of warmer weather (>10°C) to hatch. Therefore, eggs passed out by lambs in spring/summer hatch in a synchronised manner the following spring and thus infect the following year's lamb crop. Lambs rapidly develop strong immunity to Nematodirus and usually have protective immunity by approximately 12 weeks of age.