Populations of free-living stages of Ostertagia ostertagi and O. circumcincta in a winter rainfall region

Abstract

Pats of cattle faeces containing eggs of the trichostrongylid Osferfagia ostertagi and deposits of sheep faecal pellets containing eggs of O. circumcincta were placed on dry and irrigated pasture plots at four times during the period October 1977 to February 1978. Faecal pellets lost moisture far more rapidly than did dung pats. The rate of moisture loss from both faecal deposits was greater on dry plots than on irrigated plots. Despite large differences between irrigated and dry plots in soil temperature and soil and pasture moisture status, the temperatures recorded in both dung pats and faecal pellets were similar on all plots at each time of deposition. A significantly greater proportion of O . circumcincta eggs was recovered as infective larvae in faeces, on herbage and in soil compared with that of O. osterfagi eggs. Irrigation did not result in either substantially more eggs developing to infective larvae in faeces or higher recoveries of larvae from herbage and soil. No significant differences were detected in temperature or moisture measurements or in parameters of free-living development and larval survival between plots with long or short pasture herbage. There were marked differences between the population dynamics of the infective larvae of Ostertagia spp. and between the numbers of larvae on irrigated and dry plots. On dry plots, O . circumcincta migrated in abundance from faecal deposits after smaller falls of rain than were required for migration of O . ostertagi larvae. Larvae of both species persisted in abundance on the herbage of most dry plots until late spring. On irrigated plots, migration of both species of larvae occurred immediately and was independent of rainfall, but survival rate of larvae was lower than on the corresponding dry plots.