Legume addition to alfalfa-based mixtures improves the forage energy to protein ratio

Alfalfa (Medicago sativa L., AL)-based forage mixtures are a major constituent of ruminant rations, and optimizing their energy-to-protein ratio has been identified as a way to improve N use efficiency. This study aimed to determine whether the energy-to-protein ratio could be improved by adding red clover (Trifolium pratense L., RC) or birdsfoot trefoil (Lotus corniculatus L., BT) at different seeding proportions, and/or one grass species [timothy, Phleum pratense L., or tall fescue, Schedonorus arundinaceus (Schreb.) Dumort] to AL. Annual forage yield, species proportion in botanical composition, and nutritive value of forage were measured at three sites in Canada for 2 post-seeding years. The addition of RC or BT did not affect the annual forage yield but it increased the concentration of forage nonfiber carbohydrates (NFCs), particularly of soluble sugars, and decreased concentrations of crude protein (CP), nonprotein nitrogen (NPN), and rapidly degradable protein (PB1) of AL-based mixtures. The addition of one percentage unit of RC or BT to forage botanical composition improved the NFC/CP ratio by 0.005, and the NFC/(NPN + PB1) ratio by 0.024. The addition of either grass species to AL mixtures also increased the two ratios, but it was related to a CP decrease with no increase in NFC concentrations. Adding RC or BT to AL-based mixtures is therefore a valuable strategy to increase the forage energy to protein ratio.