Factors regulating tapeworm populations: dispersion patterns of Taenia hydatigena eggs on pasture.

Two grazing trials using 'sentinel' lambs were undertaken to measure changes in the availability of eggs within 30 metres of deposition by dogs infected with Taenia hydatigena. In the first trial the experimental pasture was divided into nine equal plots; in the second trial, each of the nine plots was divided into sub-plots. In each trial, infected dogs were placed on the pasture for 10 days. Lambs were then grazed for 10 days immediately, 36 days and 56 days after the dogs had been removed. Changes in the dispersion pattern of the eggs over time and space were assessed by examination of the lambs for cysts at autopsy. In both trials, eggs spread radially within the grazing zone within 10 days, but 36 days after the removal of the dogs, their availability to the lambs was markedly reduced. In the first trial at five weeks, the height of grass (between 3 cm and 15 cm) did not modify egg availability. In both trials, despite differences in rainfall affecting the growth of grass and associated factors similar egg losses occurred.