Options for parasite control using tanniferous forages in livestock in Northern temperate areas

Summary

Leguminous forages with a relatively high level of condensed tannins (CT)(4-8 % of DM) fed to sheep may lead to lower faecal nematode egg counts and worm burdens. Scottish studies using a CT, quebracho in the diet have con-firmed this effect in Trichostrongylus colubriformis infections, and Danish in vitro studies have indicated a direct effect of purified CTs on preparasitic sta-ges of ovine nematodes. The legumes greater trefoil (Lotus pedunculatus), sulla (Hedysarum coronarium), sainfoin (Onybrychus viciifolia) and birdsfoot trefoil (L. corniculatus) are presently of major interest. In Denmark, nematode infected lambs grazing pure stands of sulla and sainfoin for 5 weeks have shown up to 50% reductions in egg counts compared to grazing clover. A Swedish study in lambs found no effect on worm counts of 15% (DM) birds-foot trefoil in the diet. Preliminary results have thus been promising but the fol-lowing problems have to be addressed for a future, successful application of tanniferous forages in nematode control in Northern temperate areas:
1. Species better suited locally should be found. Sainfoin is not competitive in leys, and weeds dominate, particularly in organic farming without herbicidal use. Sulla, a Mediterranean plant, do not overwinter.
2. Efficacy relatively low. Knowledge of the mechanism of action may indicate ways of improving the efficacy. Selection of appropriate cultivars or growing conditions is needed.
3. The activity in cattle and goats needs to be investigated.
4. The forages need to be integrated in other systems of control, most likely repeated moves or biological control. The implementation is governed by the seasonality of the forages and the epidemiology of the infections.