Migration of gastrointestinal nematode larvae from cattle faecal pats onto grazable herbage

This study investigated the effect of successive harvests of grazable herbage around cattle faecal pats on the population dynamics of infective gastrointestinal nematode larvae (L3). Faecal material, collected from naturally infected calves, was deposited as pats during summer, autumn and winter on three different topographical aspects within a moist, temperate region of New Zealand. Herbage was harvested four times (22–248 days) from around the faecal pats to a height of 2 cm in three radial zones (0–20 cm, 20–35 cm and 35–45 cm from the centre of the faecal pat) and L3 extracted. Harvest date was determined by herbage mass to simulate grazing events.L3 extracted from herbage were predominantly Cooperia spp. More L3 were recovered from faeces deposited in summer and autumn, than those deposited during winter. L3 concentration on herbage was highest (P < 0.001) in the zone nearest the pat for all except the fourth harvest. Mean concentrations of L3 on herbage were 11,447, 3154, 337 and 102 L3/kg dry matter herbage, for the four successive harvests, respectively. Microclimate differences as affected by aspect had a marked effect on herbage growth, but did not significantly affect L3 concentration on herbage.In this study, L3 remained aggregated close to the faecal pats they emerged from even after two successive harvests and significant rainfall. Successive harvests simulated the effect of repeated grazing events by a non-infective stock class. Two such grazings and the associated time, reduced L3 presence on grazable herbage to <3% of the original population. Grazing strategies to generate clean pasture for vulnerable cattle are discussed in relation to these results.