The Histotropic Phase and Other Biological Aspects of Ostertagia ostertagi

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Abstract
The present report attempts to show that a correlation between the duration of the histotropic phase and developmental inhibition, such as reported by Sommerville (1953) for O. circumcincta, exists also for O. ostertagi. This histotropic phase may terminate at 96 hours, at 5 days, at 7 days, at 10 days, at 12 2/3 days, or at 15 days to 3 months postinfection. Retardation in the growth of the parasite at various stages of development is noted in 2 calves, one of which received multiple doses of larvae and the other a small single dose of 1000 larvae. Necropsies of 27 beef yearlings show a high frequency of young male and female worms in the abomasal mucosa. They showed various stages of emergence. It is suggested that since gravid females are rarely found in the mucosa younger females must escape in order to copulate. Some of these gravid females oviposit in the gastric pits.

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