Production and parasitological responses of lambs exposed to differing low levels of trichostrongylid larvae on pasture

Abstract

Differing numbers of trichostrongylid nematode infective larvae were established on pasture by differential seeding of 4 suites of paddocks, in order to ascertain the effect of various levels of larval exposure during autumn and winter on the parasitological and production responses of young sheep. A fifth suite of paddocks was maintained uncontaminated prior to stocking by experimental lambs. Significant differences in liveweight gain and wool production (maximum means 5.8 kg and 0.57 kg respectively) resulted from relatively small differences in the levels of larvae recorded on pasture, although numbers were exceptionally low (maximum 177 larvae/kg herbage). Neither the attainment nor timing of ‘self-cure’ by the animals on the 4 contaminated suites of paddocks appeared to be affected by the low levels of larvae available. The levels of larvae (maxima between 69 and 177 larvae/kg herbage) appeared to be above the threshold required to stimulate or permit the normal development and expression of host resistance in young sheep which had previously experienced untreated infection in spring and summer. © 1982 Taylor & Francis Group, LLC.