1.   Another more recent theory is that, in response to the presence of the adult parasites, the zymogen cells secrete increased amounts of pepsin directly into the circulation.

2.   The well developed buccal capsule of the adult parasite is prominent as is the bursa of the male.

3.   The adult parasites live in the caecum and colon.

4.   First, the high fecundity of the adult female parasite, some infected foals passing millions of eggs in the faeces each day.

5.   If untreated, the adult parasites, known as trematode worms, travel to the liver and grow to a centimeter in length.