Outbreaks of early-season trichostrongylosis in calves in Denmark.

This paper describes clinically manifest infections occurring as early as June and early July in first-season grazing calves in Denmark during the period 1972-1987. Two severe outbreaks in 1976, included in our experiments, were studied in detail. Herbage infectivity was particularly high in grass tufts surrounding cow pats that were present in high numbers around the time of turnout. It is hypothesized that the preceding extremely dry summer followed by a hard winter had indirectly retarded degradation of dung pats and thereby favoured the overwintering of the larval populations in the dung reservoirs. In a third experiment, conducted in the same year, the epidemiological pattern was more normal; presumably due to artificial irrigation of the pasture during the drought. Early-season cases that were recorded in 1980 and 1987 could possibly be related to cold winters and/or very early turnout. The findings are discussed in the light of ecological factors responsible for the breakdown of cow pats. The clinical implications are seen in relation to current control methods.