Feasibility of herbage sampling in large extensive pastures and availability of cattle nematode infective larvae in mountain pastures.

Herbage sampling has been used to ascertain the contamination and epidemiology of cattle nematode infective larvae in large extensive pastures situated in the centre of France, where heifers graze for four months on a total area of one ha/heifer in mountains virtual "hectares", tufts of grass being picked both close to faecal pats or "refusals", and far from these pats. Ostertagia was the predominant parasite and the occurrence of Dictyocaulus resulted from silent-carrier heifers. Just after the thawing of the snow, when the heifers arrived in the mountains, the contamination was very high: 8000-9000 L3 and 45.00 to 63.00 L3 kg-1 dry herbage, respectively, far from and close to faecal pats, but this contamination decreases regularly during the season. The sampling of four areas (four "hectares") in each paddock was found to be a very valuable method. The variation of the mean was low and found mainly when the number of larvae was high (6-19% only for the spring sampling). This technique could have some merit in parallel or concurrently with tracer calves which are always difficult and expensive to use.