Further observations on the effect of different levels of larval intake on the output of eggs of Ostertagia circumcincta in lambs.

Three groups of lambs were given 50, 250 or 2800 infective larvae of Ostertagia circumcincta per day for a period of six weeks. All groups then received 25,00 larvae per day for a similar period and observations were continued for a further six weeks. Egg output following the initial infection varied directly with the level of larval intake, but fell to a low during the second period of infection and decreased still further in the final six weeks of the observation. The investigation suggests that, provided high levels of residual larval infection on pasture are avoided, there appears to be considerable merit in exposing lambs to a low level of initial infection.