[Dynamics of infestation with gastrointestinal strongyles of moors grazed by sheep in the Mediterranean area].

The dynamics of free-living stages of sheep Nematodes was studied. The kinetics of infective larvae population was established during 16 months by sampling grass and faeces every 2 wk on an area frequently used by ewes on 3 out of 4 paddocks grazed by a flock. The periods at high risk for animal infection were autumn and spring, the moors being sterilized during summer by the dryness. Teladorsagia circumcinta, Trichostrongylus vitrinus, Nematodirus filicollis and N. spathiger were the main species. Free-living populations were quantified during the grazing seasons on 2 out of the 5 paddocks grazed by a second flock. Herbage and faeces were sampled on 12 areas from each paddock. Deposited eggs on each area were calculated at each rotational cycle by coproscopy and by estimating the amount of faeces deposited on the ground. Faeces appeared to be the main reservoir of infective larvae during the dry periods of spring and autumn. With rainfall the larvae were liberated from faeces and the populations on herbage increased steeply. The distribution of larval populations on the moor were highly correlated to the distribution of the eggs deposited during the preceding grazing cycle.