The development, composition and maintenance of experimental populations of Haemonchus contortus in sheep

Clun Forest sheep, aged between 3 and 18 months and worm-free from birth, were given a single dose of 25 000 infective larvae of the nematode Haemonchus contortus. The host animals were killed between 4 and 100 days after infection and the nematode populations were examined to determine size and composition. The relation between worm body length, dry weight and age was studied and growth curves were constructed. Variations in the sex ratio for infections of different ages were noted. No evidence was found for a relation between rate of growth and population density. The rate of expulsion was determined and its variability discussed.