Seasonal changes in abomasal worms (Ostertagia spp.) in white-tailed deer (Odocoileus virginianus) at Long Point, Ontario

Abstract

Three species of nematodes were recovered from the abomasa of white-tailed deer (Odocoileus virginianus) collected at Long Point, Ontario, from September 1972 to August 1973. Ostertagia odocoilei was recovered from 45 deer (96%), O. mossi from 31 (66%), and O. dikmansi from 30 (64%). Abundance of adult stages of all three species was greatest in summer and least in winter. O. odocoilei was the most abundant species, especially during winter. Females were more abundant than males at all times of the year, particularly during winter.Numerous inhibited early fourth-stage larvae were recovered during winter and early spring, while few were found in July and August. The decrease in numbers of inhibited larvae in spring was coincident with a corresponding increase in abundance of adult worms. This is the first indication of the existence of inhibition (previously reported in domesticated animals) in species of Ostertagia parasitizing deer. Inhibition was not related to host age, indicating that the phenomenon is probably not due to development of immunity by the host over the grazing season.