Methane yields from Brahman cattle fed tropical grasses and legumes

Abstract

<jats:p>In the national greenhouse inventory, methane emissions from the Australian tropical beef herd are derived from cattle fed two diets. In the experiments reported here, methane production was measured by open-circuit gas exchange from 13 Brahman cattle offered 22 diets from combinations of five tropical grass species and five legumes, with a minimum of three steers per diet. All diets were offered daily ad libitum, with the exception of three legume diets fed without grass and leucaena (Leucaena leucocephala) mixed with grass, which were offered at 15 g dry matter per kg liveweight. Diets were fed as long-chopped dried hay, with the exception of leucaena, which was harvested and fed within 2 days. For the data from cattle fed diets of grass and grass mixed with legumes, methane production could be predicted as 19.6 g/kg forage dry matter intake (residual standard deviation 12.3). Observed methane yields were not predictable from a stoichiometry, which used volatile fatty acid proportions in rumen fluid. Mean methane emission rates across all diets were equivalent to 8.6–13.4% of digestible energy intake, and 5.0–7.2% of gross energy intake. The latter values are comparable to IPCC (2006) recommendations (5.5–7.5%) for large ruminants fed low-quality crop residues and by-products. Methane yields per unit of ingested dry matter or digested organic matter were variable across diets but were related to digestibility and contents of fibre and protein. These results constitute a significant downward revision of the methane emissions attributable to the northern Australian beef herd grazing tropical pastures.</jats:p>

Herd-scale measurements of methane emissions from cattle grazing extensive sub-tropical grasslands using the open-path laser technique

“…The mean emission value for the Lansdown site was 0.90 g/kg BW, which is outside the expected range. Kennedy and Charmley (2012) where DMI is in g/kg BW and CH 4 emission is in g/head per day. These values were then compared with predicted DMI using the equation of Minson and McDonald (1987); DMI ¼ ð1:185 + 0:00454BW À 0:0000026BW 2 + 0:315BWGÞ 2 where BWG is BW gain in kg/head per day.…”

A universal equation to predict methane production of forage-fed cattle in Australia

“…For tropical diets, gross energy (GE) concentration of the diets was also provided. This was necessitated as the mean GE concentration of tropical diets used by Kennedy and Charmley (2012) was lower than the standard value of 18.4 MJ/kg DM used for temperate forages in the present paper and in current accounting methods. For all data, a constant energy value for methane of 55.22 MJ/kg methane (Brouwer 1965) was adopted.…”

“…The tropical beef data collected on growing Bos indicus steers were previously published by Kennedy and Charmley (2012). In total, 23 diets were evaluated that included the tropical grasses black speargrass (Heteropogon contortus), buffel grass (Cenchrus ciliaris) bisset creeping bluegrass (Bothriochloa insculpta), mitchell grass (mixture of Astrebla lappacea, Astrebla elymoides) and rhodes grass (Chloris gayana).…”

“…Full details were provided by Kennedy and Charmley (2012) and Tomkins et al (2011). Briefly, in each of two chambers, animals were fed once daily in the morning at a level equivalent to the feeding level established in the previous 5 days during pen feeding.…”

“…All diets were fed ad libitum as hays and no concentrate feeds were given. Data for diets containing leucaena, presented in the original paper (Kennedy and Charmley 2012) were excluded because leucaena was shown to reduce methane emissions. Data from a further three grasses (mitchell grass hay, rhodes grass hay and a mixed Urochloa, rhodes, buffel pasture) from trials conducted in Townsville were included to expand the dataset (N. W. Tomkins, unpubl.…”