Abstract
This study determined methane emissions from enteric fermentation in Alberta’s beef cattle population by using three methodologies: (1) Intergovernmental Panel on Climate Change (IPCC), Tier 2 guidelines for cattle, (2) actual methane emission factors, expressed as a percentage of gross energy intake, from Canadian research trials and; (3) CowBytes© plus the basic equation developed by Blaxter and Clapperton (1965). Methane emissions, in carbon dioxide equivalents (CO2-E), from Alberta’s beef cattle were determined for 1990, 1996 and 2001. Census of Agriculture numbers for Alberta (Statistics Canada; www.statcan.com) were used and beef cattle were subdivided into 31 distinct categories based on animal type, physiological status, gender, weight, growth rate, activity level and age. Emission of greenhouse gases (GHG) from Alberta ’s beef cattle population, based on IPCC Tier 2 guidelines, were 4.93, 6.57 and 7.01 Mt CO2-E yr-1 in 1990, 1996 and 2001, respectively. Emissions based on methane emission factors from Canadian research trials were 6.23, 8.26 and 8.77 Mt CO2-E yr-1 in 1990, 1996 and 2001, respectively. Estimated methane emissions based on CowBytes© and Blaxter and Clapperton’s (1965) equation were 6.24, 8.35 and 8.94 Mt CO2-E yr-1 in 1990, 1996 and 2001, respectively. The IPCC Tier 2 values were 25.2–26.5% lower than the GHG emissions calculated using emission factors from western Canadian research and 26.7–27.6% lower than GHG emissions calculated from CowBytes© and Blaxter and Clapperton’s equation. IPCC Tier 1 values, which were calculated by multiplying total beef cattle in Alberta by four single value emission factors (beef cows = 72 kg CH4 yr-1; bulls = 75 kg CH4 yr-1; replacement heifers = 56 kg CH4 yr-1; calves, steer and heifer calves for slaughter = 47 kg CH4 yr-1), were 4.83, 6.40 and 6.83 Mt CO2-E in 1990, 1996 and 2001, respectively. Thus, IPCC Tier 1 GHG emissions from enteric fermentation in beef cattle were 2.0–2.7, 28.6–29.1 and 29.2–31.0% lower than those calculated from IPCC Tier 2, western Canadian research trials, and CowBytes© plus Blaxter and Clapperton’s equation, respectively. These results reflect the uncertainty associated with estimating methane emissions from enteric fermentation in cattle and suggest that further research is required to improve the accuracy of methane emissions, particularly for beef cows in their second and third trimester of pregnancy and fed in confinement. They also indicate that a more robust methodology may be to combine CowBytes© predicted dry matter intake with regional specific methane emission factors, where methane loss is expressed as a percentage of gross energy intake. Key words: Cattle, enteric fermentation, greenhouse gas, methane