The impact of season and vegetation on the survival and development of Oesophagostomum dentatum larvae in pasture plots

Pats of pig faeces containing known numbers of Oesophagostomum dentatum egg s were placed on plots with bare soil, short or tall herbage on 8 occasions during 1 year. The number of eggs and larvae and the relative distribution of larvae in faeces, soil and herbage was monitored for I year after depos ition. On 2 occasions soil from 8 selected plots was given to pigs, which w ere later slaughtered and examined for the presence of adult O. dentatum. L ess than 1% of the deposited eggs could be recovered as infective larvae. T he highest recoveries were generally made on tall herbage plots. The majori ty of infective larvae was found within the faecal pats, which indicates th at infective 0. dentatum larvae, to a large extent, do not disperse onto th e herbage or into soil. The infective larval stage was reached only when th e mean temperature in the weeks post-deposition was above 10 degreesC. This stage was reached within I week when the mean weekly temperature was above 13 degreesC. After the winter period no infective larvae could be recovere d from any plots and no parasitic worms could be isolated from pigs fed soi l from 8 selected plots.