Reducing Carbon Dioxide Equivalent Emissions By Finishing Beef Yearlings on Birdsfoot Trefoil Perennial Legume Pastures.

The conclusion from life cycle assessments (LCA) of beef finished on grass pastures compared with feedlot finishing is that the carbon dioxide equivalent (CO₂ eq.) footprint per kg of meat is lower for grain-based feedlot finishing than for pasture-based finishing. However, the lower CO₂ eq. footprint of feedlot systems in these studies was due to the relatively low average daily gains (ADG) of cattle on grass pastures (e.g., 0.6 kg d^-1) compared with feedlot ADG (e.g., 1.4 kg d^-1). Birdsfoot trefoil (Lotus corniculatus L.; BFT) is a nitrogen-fixing, deep-rooted perennial legume that performs well under irrigation in the dry, high-elevation climate of the northern Mountain West USA. The fiber content of legumes is less than that of grasses, and digestion and intake are greater than for grasses, resulting in higher rates of ruminant gain. Birdsfoot trefoil has a low concentration (10-40 g kg^-1 dry matter) of a unique condensed tannin that binds reversibly with proteins in the rumen, preventing bloat, but releasing proteins in the abomasum. Birdsfoot trefoil tannins allow protein digestion and amino acid absorption in the small intestine. Yearling Angus steers with an average initial weight of 451 kg were assigned to one of three treatments: meadow bromegrass (Bromus riparius Rehmann) pasture, BFT pasture, or a concentrate-based feedlot finishing diet. Steers gained 0.88, 1.03 and 1.42 kg d^-1, respectively, during 84 days on these diets. The use of BFT pasture finishing would reduce the LCA CO₂ eq. footprint per kg of meat compared to grass pasture finishing due to more rapid gain and biological nitrogen fixation, and is more sustainable than nitrogen-fertilized, annual cereal grain-based feedlot finishing systems. Future LCA of beef production on pasture should include the finishing of cattle on high-quality, well managed perennial legume pastures as well as grass pasture finishing.