Tackling sheep worms in dry summer environments

摘要

Nematode parasites of sheep (worms) have two stages to their life cycle, a parasitic stage - the worms inside the sheep, and a free-living stage - the eggs and larvae on the ground. There is a constant movement between the two stages, with eggs fromthe parasitic stage moving in faeces to the ground and infective larvae from the free-living stage on grazed pastures moving into the sheep. At different times of the year the proportion of the overall worm population in each stage will vary. The numberof free-living worms will depend on: the number of eggs coming from the sheep; the hatching and development of the eggs; and the survival of the eggs and larvae. The number of parasitic worms will depend on: the number of available infective larvae on the pasture; and the resistance of the sheep to the parasites.