Further observations on faecal egg output in lambs dosed continuously with Ostertagia circumcincta.

The relationship between size of intake of infective larvae of Ostertagia circumcincta and faecal egg output by lambs was examined in two experiments in four-month-old Suffolk cross lambs dosed five times per week for 10 weeks. The first experiment compared two strains, Weybridge and Moredun, at two levels, 400 and 4000 per dose. The second experiment compared two levels, 40 and 400 per dose, of Moredun larvae. The group mean output of worm eggs was almost unaffected by the 10-fold reduction in intake from 4000 to 400. The further reduction from 400 to 40 reduced egg output by a factor of 2.5.