α-Tocopherol and β-carotene concentrations were measured in herbage of birdsfoot trefoil (Bft), red clover (Rc), white clover (Wc), timothy (Ti) and perennial ryegrass (Pr) grown in four mixtures (Bft+Ti, Rc+Ti, Rc+Pr and Wc+Pr) in a small-plot field experiment at Foulum, Denmark, over 2 years. Plots were fertilized with cattle slurry and harvested in a four-cut system: 30 May/7 June, 5 July/12 July, 22 August/21 August and 24 October/9 October in 2005/2006. Bft was the legume with the highest α-tocopherol concentration in most harvests [86 mg kg−1 dry matter (DM) averaged over all harvests of 2 years], whereas mean α-tocopherol concentrations in Wc and Rc were 37 and 34 mg kg−1 DM respectively. Bft and Wc had higher β-carotene concentrations than Rc when averaged over harvests and years (80, 67 and 44 mg kg−1 DM in Bft, Wc and Rc, respectively; P < 0·0001). Vitamin concentrations were similar in harvests 1–3, but in most sward treatments they were considerably higher in harvest 4. No clear differences were found between years. Averaged over years and harvests, mean α-tocopherol concentrations in timothy and perennial ryegrass were 46 and 50 mg kg−1 DM, respectively, and mean β-carotene concentrations were 54 and 62 mg kg−1 DM. In conclusion, herbage of birdsfoot trefoil generally had higher vitamin concentrations than white or red clover, but differences between the two grass species were small and inconsistent.