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SUMMARYProtein in forage legumes is often poorly utilized by ruminants and high nitrogen (N) losses are expected. The objective of the present study was to investigate the effects of forage legumes (white clover, WC; red clover, RC; lucerne, LG; and birdsfoot trefoil, BT) in binary mixtures with perennial ryegrass (G) under different defoliation systems (silage, simulated grazing and grazing) on agronomic performance and forage quality. A high proportion of legumes may favour dry matter (DM) yield and the defoliation system may reduce the persistence of certain forage legumes, with a negative influence on the energy and N yield. Annual DM yield under grazing was highest for WC mixtures (WC+G, 1059·2 g DM/m²) compared to all other mixtures, confirming its adaptation to grazing. Mixtures with RC (RC+G) and LG (LG+G) performed similarly to WC+G, whereas BT mixtures (BT+G) were less competitive under more intensively used systems. Analyses of crude protein, cell wall characterization and protein fractionation showed a three-way interaction between year, mixture and defoliation system. RC and BT resulted in a positive protein quality of the mixtures, probably due to their content of secondary plant compounds. In conclusion, different forage legumes did not perform equally in the cutting and grazing systems, and both legume species and defoliation systems interacted in the production of forage of high protein quality for ruminant nutrition.

Only a few previous studies have analysed the crude protein (CP) fractions of the Cornell Net Carbohydrate and Protein System during the growth period of forage legumes. The objective of the present study was to investigate the changes in CP fractions during the spring growth and summer-autumn regrowth period of five forage legume species (alfalfa (also known as lucerne, Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), kura clover (Trifolium ambiguum M.B.), red clover (Trifolium pratense L.) and white clover (Trifolium repens L.)) grown in binary mixtures with perennial ryegrass (Lolium perenne L.) and also in pure stands (two red clover cultivars). Additionally, the specific polyphenol oxidase (PPO) activity was measured photometrically in the leaves of pure red clover swards. In both pure and mixed cropping, CP fraction A increased with advancing maturity, except for the legumes from mixed cropping in the summer-autumn growth period 2004 and 2005. The variation of CP fraction A was mostly positively related to the N yield and the amount of dinitrogen fixation. Although CP fraction A of pure red clover was negatively correlated with the specific PPO activity in the spring growth period, the specific PPO activity was less relevant for the variation of CP fraction A with respect to the whole growing season. CP fraction B generally made up the largest proportion of the CP. Pure red clover stands showed reducing amounts of CP fraction C during the growth period, whereas in legumes grown with ryegrass an increase was usually observed. Despite these differences, there was generally an increase of CP fraction C when the content of nonstructural carbohydrates decreased. Red clover and birdsfoot trefoil herbage contained the highest proportions of CP fraction C in the CP, regardless of growth period and year. In conclusion, red clover and birdsfoot trefoil had a more favourable CP composition for ruminant nutrition compared to the other legume species, and in red clover this could not be clearly attributed to the specific PPO activity.

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