[The effect of dehydration of ovine feces on the development of free-living stages of gastrointestinal strongyles].

The amount of water lost out of the fresh faeces during the first hours after they are laid is dependent on the hour, the site and the nature (isolated or aggregated dropping) of the faecal deposit. We studied the effect of desiccation by deposing contaminated faeces in different natural conditions. It appears that the number of infective larvae for one hundred deposited eggs is higher when the rate of desiccation is slower, mainly for O. circumcincta. The results for T. colubriformis and H. contortus are more variable, the number of larvae being lower. N. spathiger is less sensitive to the desiccation. In laboratory experiments, the optimum humidity of faeces, as far as the development rate is concerned, extended from 60 to 65%. With higher and lower levels, the developing rate rapidly decreases. N. spathiger is hardly more resistant to low levels of water content. Embryonated eggs and infective larvae are the most resistant stages, mainly for O. circumcincta. The importance of desiccation of fresh faeces during the first hours after deposition and the viability of Trichostrongyle eggs is discussed.