[Effect of temperature and humidity on gastrointestinal strongyle infestation of bovine pastures]

Two pastures, one grazed by heifers and one by cows were sampled for larval counts from August to November 1982 at different intervals of time from seven days to half an hour. Ostertagia sp. and Cooperia sp. were highly dominant. The population level was higher in heifer pasture, but maximal and minimal numbers were observed the same days on the two pastures, close to and at a distance from the cow-pats. During the four months, numbers of larvae were higher during rainy weeks. The rain mainly had an effect on Ostertagia populations, the minimum temperature mainly on Cooperia. In more than 50% of observations made on two consecutive days, the number of larvae one day was less than twice (or half) of those observed the preceeding day. In one case out of ten this number was more than four times as great. This variation from one day to the other was correlated to the temperature magnitude. The rainfall had a positive or negative effect depending on its intensity. During the day-time, more larvae were observed in the morning, the population decreasing with air humidity. During these summer and autumn periods, climatic factors had effects mainly on larval migrations: lateral migrations from cow-pats to herbage, vertical migrations on grass.