Condensed tannins and gastro-intestinal parasites in sheep

Abstract

As the effectiveness of current anthelmintic drenches is being reduced by the emergence of drench resistance and significant production losses may still occur as a result of continuing larval challenge, strategies for nematode control should focus on preventing the build-up of infective larvae on pasture rather than treating the infection. This paper reports the effects of condensed tannins (CT) extracted from Lotus pedunculatus, Lotus corniculatus, sulla (Hedysarum coronarium) and sainfoin (Onobrychus viciifolia) on in vitro viability of eggs, first stage larvae (L1) and third stage larvae (L3) of the sheep nematode, Trichostrongylus colubriformis. When in vitro assays contained CT in a similar concentrations to that in the digestive tract of sheep fed these forages, the CT reduced the development of eggs to L3 larvae as well as the proportion of eggs hatching. The CT also reduced the development of L1 larvae to L3 larvae and decreased the motility of L3 larvae when assessed by the larval migration inhibition assay and this may reduce their infective capacity in vivo. If these forages are fed to grazing sheep, then it may be possible to reduce contamination of pasture with infective larvae and reduce our dependence on anthelmintics as the principal method for controlling internal parasites. Keywords: condensed tannins, drench resistance, egg hatching, larval development, Lotus, parasites, sainfoin, sulla, Trichostrongylus colubriformis