New factors affecting the epidemiology of bovine ostetagiasis

This thesis is divided into 5 Chapters. In the first, following a general introduction, there is a comprehensive review of the literature pertaining to the pathogenesis, epidemiology, treatment and control of bovine ostertagiasis. Chapter 2 described the materials and methods. In Chapter 3, for the first time a sequential study is made on the population of bovine Ostertagia spp. infective larvae in the soil. Herbage and stratified soil samples from a previously grazed calf pasture were collected regularly over a 12 month period in 1979 and 1980 and infective larvae were present on each sampling occasion to a depth of at least 15 cm. Analysis of the vertical distribution of the larvae suggested a possible downward migration in the winter followed by an upward trend in the spring and summer. This interpretation was based on a statistical anlysis of both the actual larval numbers present and the positivity of each sample collected. Most important was the finding that the numbers of Ostertagia L present in August 1980 at the interface between soil and pasture was estimated at 6.4 X 10