Observations on the Epidemiology of Parasitic Gastro-enteritis in Calves

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Abstract
Over a period of seven years several series of observations were made on infestations of Ostertagia ostertagi and Cooperia oncophora on the herbage of pastures grazed by calves. A regular seasonal pattern was revealed. The concentration of larvae on the herbage falls to a low level in spring. Susceptible calves turned out at this time may begin to contaminate the pasture in mid-May but it is not until July that the infestation on the herbage increases significantly. Generally the increase is to a high level which is maintained with little change until the following spring.Evidence is presented which indicates that contamination of the pasture in the first half of the grazing season is far more effective in the production of an infestation on the herbage than is contamination in the second half of the season.In a discussion of the epidemiology of parasitic gastro-enteritis the formerly accepted view, that clinical helminthiasis results from a continuous build-up of infection in the calves and on the pasture is rejected. It appears that the parasites complete little more than one generation each year.The results of these observations suggest a simple and widely applicable means of controlling parasitic gastro-enteritis in calves.