Methane and carbon dioxide emissions from crossbred beef cattle grazing native pastures
Citation
Behrouzi A., Fitzsimmons C., McKeown L., Basarab J., Bork E. 2022. Methane and carbon dioxide emissions from crossbred beef cattle grazing native pastures. Poster and talk at the 8th International Greenhouse Gas & Animal Agriculture Conference, Orlando, FL, USA. June 2022.
Plain language summary
Enteric methane from ruminants accounts for about 6% of global man-made greenhouse gas
emissions, which vary with feed efficiency. Past studies measuring methane emissions in beef cattle
have often used drylot conditions with uniform diets. To better understand methane production from
cattle grazing diverse diets on open-range, we quantified methane and carbon dioxide production from
beef cattle previously measured for feed efficiency in drylot. In addition, cattle were measured while grazing two different pasture conditions. Crossbred beef cows and heifers were monitored using the GreenFeed emissions monitoring (GEM) system for 26 ± 12 days in each pasture to collect their methane and carbon dioxide emissions (g/day). Cows had higher average methane and carbon dioxide yield than heifers during the day. Cattle emitted less daily methane and carbon dioxide when grazed on summer pasture compared with fall pasture. A positive relationship was evident between cow methane emission and feed efficiency during fall grazing. Similarly, carbon dioxide emission was positively related to cow feed efficiency in both pastures. In conclusion, beef cattle methane emissions increased from summer to fall with older vegetation. Although other factors might also influence enteric methane emissions of cattle grazed on higher quantity-lower quality pasture,
feed efficiency, measured in a feedlot setting, can explain a small but significant proportion of this variance.
Abstract
Enteric methane (CH 4 ) from ruminants accounts for about 6% of global anthropogenic greenhouse gas
emissions, which vary with feed efficiency. Past studies measuring methane emissions in beef cattle
have often used drylot conditions with uniform diets. To better understand methane production from
cattle grazing diverse diets on open-range, we quantified CH 4 and carbon dioxide (CO 2 ) production from
beef cattle previously measured for residual feed intake, adjusted for off-test backfat thickness (RFI fat ), in
drylot. In addition, cattle were measured while grazing two different pasture conditions (SUM: higher
quantity and quality in summer, vs. FAL: higher quantity but lower quality in fall). Crossbred beef cows
(n=34) and replacement heifers (n=19) were monitored using the GreenFeed emissions monitoring
(GEM) system for 26 ± 12 days in each pasture to collect their CH 4 and CO 2 emissions (g/day). Cows had
higher average diurnal CH 4 (SUM: 260.1 ± 3.1 vs. 193.3 ± 4.3; FAL: 290.4 ± 3.0 vs. 230.0 ± 4.0) and CO 2
yield (SUM: 9297.6 ± 92.3 vs.7010.7 ± 124.9; FAL: 9250.5 ± 90.8 vs. 7327.5 ± 121.9) than heifers (P<0.01). Cattle emitted less daily CH 4 (-16% for heifers; -10.4% for cows) and CO 2 (-4.3% for heifers) when
grazed on summer pasture compared with fall pasture (P<0.01). A positive relationship was evident
between cow CH 4 emission and RFI fat (R 2 = 0.008; P<0.05) during fall grazing. Similarly, CO 2 emission was positively related to cow RFI fat in both pastures (R 2 = 0.015; P<0.01). In conclusion, beef cattle CH 4
emissions increased from summer to fall with advancing vegetation senescence. Although other factors
might also influence enteric CH 4 emissions of cattle grazed on higher quantity-lower quality pasture,
RFI fat , measured in a feedlot setting, can explain a small but significant proportion of this variance.