Abstract
Greenhouse gas emissions from ruminant livestock production systems contribute significantly to the environmental footprint of agriculture. Emissions are lower for feedlot systems than for grass-based systems primarily because of the extra time required for grass-finished cattle to reach slaughter weight. In contrast, legume forages are of greater quality than grasses, which enhances intake and food conversion efficiencies, leading to improvements in production and reductions in environmental impacts compared with forage grasses. In addition, the presence of certain bioactives in legumes such as condensed tannins (CT) enhance the efficiency of energy and protein use in ruminants relative to grasses and other feeds and forages. Grazing tannin-containing legumes also reduce the incidence of bloat and improve meat quality. Synergies among nutrients and bioactives when animals graze diverse legume pastures have the potential to enhance these benefits. Thus, a diversity of legumes in feeding systems may lead to more economically, environmentally, and socially sustainable beef production than grass monocultures or feedlot rations.
Highlights
Emissions of greenhouse gases (GHG) from ruminants include methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) [1]
142 Tg CO2eq are directly emitted from cattle systems (CH4 and N2O from enteric fermentation and manure management), which is nearly 60% of the total GHG emitted for beef cattle production [1], or 2.1% of the total US anthropogenic GHG emissions [2]
This study demonstrated that the partial replacement of alfalfa by sainfoin and birdsfoot trefoil in 2-way or 3-way choices was effective in reducing the urinary N concentrations of beef heifers
Summary
Emissions of greenhouse gases (GHG) from ruminants include methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) [1]. Many ruminants consume forages as their sole diet in pasture-based livestock systems, and the need to supply feed additives in meals might constrain their practical implementation [21] In this case, CH4 emissions may be reduced by using highly digestible forage species with a low concentration of fiber [30,31], because forages such as grasses with high fiber concentration reduce passage rate and increase ruminal retention time [32,33], which enhances CH4 production per unit of forage intake (CH4 yield). It has been estimated that the number of cattle required to produce 1 billion kg of beef when finished on pure birdsfoot trefoil pastures is approximately 15% lower than when finished on grass (2.9 vs. 3.4 million animals, respectively; [48]), suggesting that legume-finishing systems represent a realistic strategy to reduce enteric CH4 emissions
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