Effect of Temperature on Development of the Free-Living Stages of Ostertagia ostertagi

Abstract

Hatching of the eggs of Ostertagia ostertagi was studied by recovering them from feces and incubating them in distilled water at temperatures between 4 and 40 C. The hatching occurred at temperatures between 4 and 35 C. The rate of development increased with the rise of the temperature. The development of the infective larvae was studied in fecal cultures. The infective larvae developed between 10 to 35 C. The optimum temperature for development was 25 C. The speed of development increased with the rise of temperature but the percentage recovery decreased at higher and lower temperatures. The size of the newly hatched larvae varied with the temperature at which they developed, being biggest at 15 C and smallest at 35 C. The size of the infective larvae grown at different temperatures varied. The maximum size was at 20 C and it decreased at temperatures above or below this. Like other trichostrongylid nematodes, Ostertagia ostertagi, which inhabits the abomasum of cattle, passes a part of its life cycle as freeliving stages outside the host. During their free existence these stages are subject to the effects of a large number of biotic and climatic factors existing in their microenvironment. From field experiments it is difficult to assess the importance or effect of individual factors and therefore the investigator must resort to controlled laboratory experiments. Temperature is one of the most important factors in the development of the free-living stages. Rose (1961, 1962) and Kutzer (1967) made some observations on the effect of temperature on the development of free-living stages of 0. ostertagi but since their primary interests were to study the ecology of these stages, their observations were of a very limited nature. The objective of the study reported here was to observe the effects of various constant temperatures on the development of the free-living stages of 0. ostertagi. MATERIALS AND METHODS A pure monospecific infection of 0. ostertagi was established in a worm-free calf by administering the infective larvae. For all experiments feces were collected directly from the rectum between 30 to 60 days after administration of the infective larvae to the calf.