Phalaris staggers is a toxic diseases occurring in the sheep. It is caused by a toxic substance that gathers in the young shoots of the perennial (lives for more than two years) grass phalaris.
Flatworm - Liverfluke
Sheep Blowfly
Liverfluke are parasite that live in an animals digestive system. Large numbers of flatworm can cause weight loss, anaemia (loss of red blood cells) and eventually death.
Sheep blowfly is where blowfly lay their eggs in warm, moist areas os sheep's wool - normally around the breech region. It can cause skin infection and irritation.
Source - Dynamic Agriculture Book three - Brown Hindmarsh and McGregor