The origin and overwintering survival of the free living stages of cattle parasites in Sweden

During the 1997 Swedish grazing season, faeces were collected every 3 weeks on 7 occasions from young grazing cattle with moderate nematode parasite i nfections. From this source 12, 400 g dung pats were set up on each samplin g occasion on a specially designated area of pasture. Half of these pats we re placed on pasture where it was aimed to prevent snow cover during the su bsequent winter. During the grazing season, herbage growth was kept at reas onably uniform height by clipping and the dung pats were protected from des truction by animals and birds. At the time of animal turn-out the following year (7(th) April 1998), it was observed that all dung pats had disappeare d. Assessments of the survival of infective larvae, both on pasture and in soil, were made in a circular area encompassing the location of each pat. T hese sampling procedures were completed within a 3 week period. All faecal deposits yielded infective larvae at turnout the following year, with propo rtionally greater numbers developing from nematode eggs deposited in cattle dung during the mid third of the previous grazing season. The surface laye r of soil was found to be an important reservoir for infective larvae, with numbers recovered being approximately half those found in the overlying pa sture samples. No significant differences were found between the normal pas ture and snow excluded pasture in the number of infective larvae recovered from both pasture and soil samples. The epidemiological consequences of the se findings are discussed.