Population study of bovine Ostertagia spp infective larvae on herbage and in soil.

Herbage and stratified soil samples from a previously grazed calf pasture were collected regularly over a 12 month period (October 1979 to September 1980). Infective larvae of cattle Ostertagia spp (OL3) were present on each occasion to a depth of at least 15 cm. Analysis of the vertical distribution of the OL3 suggested a possible downward migration during the winter, followed by an upward trend in the spring and summer. The number of OL3 present in the root mat in august 1980 was estimated as 6.4 x 10(6) per hectare, a similar figure to that estimated for the previous November (6.6 x 10(6)) despite the absence of contamination during this period.