The use of faecal egg counts for estimating worm burdens in sheep infected with Haemonchus contortus.

Clun forest sheep, worm-free from birth, were given a single dose of 20 000 infective larvae of Haemonchus contortus. The total number of eggs/day in the faeces was recorded for 21 infections and data on population size, sex ratio and individual worm development were collected from 76 sheep. The female to male ratio was 1.28 +/- 0.07 (S.E.). The relation between increase in worm size and uterine egg content was linear. The number of eggs present in the uteri was found to be an accurate measure of eggs passed. It was shown that the daily faecal egg output is related to total parasite weight and is not a measure of the number of individuals present.