Enteric methane emissions from backgrounded cattle consuming all-forage diets

To quantify enteric methane (CH 4 ) emissions of growing cattle consuming allforage diets, a field study utilizing 144 British × Continental crossbred steers (262 ± 4 kg) was conducted during an 84-d overwintering period followed by a 56-d grazing period in one of two, grass-based pastures. Enteric CH 4 emissions were quantified using the sulphur hexaflouride (SF 6 ) tracer gas technique. During the overwintering period, four qualities of chopped alfalfa-grass silage, ranging in NDF content from 46.4 to 60.8%, DM basis, were utilized. Steers fed the lowest quality forage (60.8% NDF) had lower DMI, (6.8 ± 0.4 kg head -1 , P = 0.0075) and lower ADG (0.83 ± 0.03 kg d -1 , P = 0.0028) compared with those fed higher quality forage whose intake ranged from 8.2 to 9.1 ± 0.4 kg d -1 , with gains ranging from 1.00 to 1.06 ± 0.03 kg d -1 . Enteric emissions (% GE intake) were not influenced by forage quality across this range of NDF values; however, CH 4 losses did decrease from 6.8 to 4.7 ± 0.3% GE intake as the winter period progressed. Increased DMI, accompanied by a decrease in the proportion of feed energy lost as enteric CH 4 emissions, suggests that utilization of the lower-quality forage improved as steers reached higher body weights. Emissions were influenced by pasture quality and availability, as highest CH 4 emissions (11.3% GE intake, P = 0.0005) were observed when quality was low and DM availability was limited (738 kg ha -1 ). This study demonstrates that growing cattle consuming all-forage diets typical of those utilized in Western Canada during the winter feeding period will lose 5.1 to 5.9% of feed energy as CH 4 . Further, it has shown that emissions from growing cattle on grass-based pastures may exceed 10% GE intake – a value that is greater than those previously reported for growing cattle grazing legume-based pastures.