The regulation of egg output by Ostertagia ostertagi in calves infected once only

Analysis of the egg counts of calves infected with one dose of larvae showed that they followed exactly the same course as those of calves infected daily, rising to a peak 25–30 days after infection and then decreasing logarithmically. An experiment in which calves were infected on a single occasion with different numbers of worms showed that faecal egg counts were not a reflection of worm numbers but were limited by a separate mechanism. Evidence is discussed which suggests that the number of eggs present in a female worm is not an entirely satisfactory measure of its rate of ovulation.