The series of experiments which form the basis of the present study concentrated on evaluations of: (i) diet selection, grazing behaviour, herbage intake, and sheep performance between Holcus lanatus (Yorkshire fog) and Lolium spp. (perennial or annual ryegrass) swards both associated with Trifolium repens (White clover), and in one study with the presence or absence of Lotus comiculatus (Birdsfoot trefoil), and (ii) the effects of condensed tannins (CT) on the behaviour and performance of sheep grazing those swards. The effects of CT on sheep production were assessed by twice daily oral administration of polyethylene glycol (PEG; Molecular weight 4,000) to half of the lambs on each sward combination.