Ostertagia ostertagi in neonatal calves: establishment of infection in ruminating and non-ruminating calves.

An experiment was carried out to study the role of the ruminal function in the establishment of Ostertagia ostertagi in neonatal calves. Three groups of calves were fed either milk only (groups A and C), or hay and concentrate in addition to milk (group B) from birth. At the time of infection, ruminal function was negligible in groups A and C, whereas it was well developed in group B. Calves of groups A and B were each given 25,000 normal ensheathed infective larvae of O ostertagi and those of group C were given 25,000 infective larvae exsheathed in vitro. Daily faecal egg output and post mortem worm counts 28 days after infection were higher in calves with well developed ruminal function than those having only negligible ruminal function. In the latter group, exsheathed larvae established at a lower rate than did ensheathed larvae. The results suggest that the degree of development of the ruminal function influences the establishment of O ostertagi.