Birdsfoot trefoil and white clover were tested in pastures to see if they could help young lambs fight off worm infections. Lambs were given either trefoil or clover in their diets and were exposed to worm larvae. The study found that neither trefoil nor clover had a significant impact on controlling worm infections in the lambs. This could be because the trefoil used had low levels of tannins, the amount of trefoil in the diet was too small, or the specific type of trefoil used didn't help with worm control.