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

Abstract

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.

Cutting schedule and species composition to improve energy‐to‐protein ratios in alfalfa‐based mixtures

“…In studies of the effect of binary and complex legume-grass mixtures on the energy-to-protein ratio, the WSC/CP and NFC/(NPN + PB1) ratios were closely related and resulted in similar rankings of the different forage mixtures (Simili da Silva et al, 2013Silva et al, , 2014. In a recent study, NFC/CP and NFC/(NPN + PB1) ratios were both increased by the addition of red clover or birdsfoot trefoil to alfalfa-based mixtures (Tremblay et al, 2023). In our study, the two ratios generally varied in the same direction but the significance of the treatment effects varied among experiments.…”

“…In two previous studies of legume-grass mixtures in eastern Canada, the WSC/CP and NFC/(NPN + PB1) ratios varied among 18 legume-grass binary mixtures (Simili da Silva et al, 2013) and eight legume-grass complex mixtures (Simili da Silva et al, 2014). In a recent study, the addition of red clover (Trifolium pratense L.) or birdsfoot trefoil (Lotus corniculatus L.) to alfalfa-based mixtures increased the NFC/CP and NFC/(NPN + PB1) ratios (Tremblay et al, 2023). These results provided useful and novel information on the possibility of using forage mixtures and their species composition to improve the balance between forage energy and proteins.…”

“…The initial research on the relationship between energy-toprotein ratios and N use efficiency by ruminants used the WSC/CP ratio mostly in forage grasses. The use of the WSC/CP ratio in forage legumes and forage mixtures could be misleading as it does not take into account all the readily fermentable energy, such as starch and pectin, mostly found in these species (Tremblay et al, 2023). As well, CP consists in several fractions varying in their degradability in the rumen and using the CP concentration in the energy-toprotein ratio calculation may not reflect well the effect on the N use efficiency by dairy cows.…”