Ruminants emit methane, a potent greenhouse gas, as a by-product of microbial fermentation of plant material in their rumen. The objective of this study was to investigate the existence of natural genetic variation in methane yield (methane production per unit feed intake) among beef cattle in Australia. Two pedigreed, performance-recording research herds of Angus cattle were used. Methane production (MP) was measured on individual yearling-age cattle in two animal houses in different years. Each animal had MP measured while being fed a fixe d daily allowance of a roughage diet of approximately 9 MJ ME/kg dry matter (DM). The amount offered was calculated to provide 1.2-times the estimated energy requirement for maintenance based on the animal's bodyweight. In 2010, MP was measured using the SF6 tracer dilution method, while in 2011 MP was measured in individual-animal respiratory chambers. A total of 339 cattle comprising 62 bulls and 73 heifers in 2010, and 139 bulls and 65 heifers in 2011, were assessed for MP. Methane yield was calculated as MP per unit dry matter intake (DMI). There was variation in both traits, with an almost 3-fold range in methane yield being observed. Phenotypically, MP was moderately correlated with DMI (r = 0.33) and with animal bodyweight (r = 0.40). In contrast, the phenotypic correlation of methane yield with DMI (r = -0.26) and with animal bodyweight (r = -0.15) were negative and weak. There was a large range in the mean for methane yield by progeny of the sires of the cattle tested. Compared to the sires whose progeny had the lowest average methane yield, there were sires whose progeny had average methane yield that were 24%, 24%, 16%, 19% and 11% higher across the five groups of cattle tested. This study has provided preliminary evidence that naturally occurring genetic variation exists in methane yield in cattle.

The aim of this experiment is to investigate and demonstrate genetic variation in daily methane production (MP; g/d), methane intensity (MI; MP per unit bodyweight; g/kg) and methane yield (MY; MP per unit feed intake; g/kg). Angus cows in pedigree- and performance-recorded research herds at Industry & Investment NSW research centres at Grafton and Trangie NSW were mated in 2007 to Angus bulls that had previously been recorded for MY. Bulls that had been identified as either phenotypically high or low for MY were used as sires in the Grafton herd; unselected sires were used in the Trangie herd. In 2010 the near 2-year-old bull progeny from Trangie and heifer progeny from Grafton were measured for MP, MI and MY. There were 8 sires with progeny represented in the Trangie bull data (n=63 progeny). A wide range in least-squares (LS) sire means was observed for MP (191g/d to 233g/d), MI (0.26g/kg to 0.63g/kg) and MY (24.3g/kg to 30.2g/kg). There were 6 sires with progeny represented in the Grafton heifer data (n=79 progeny). A wide range in LS sire means was observed for MP (133g/d to 165g/d), MP (0.15g/kg to 0.55g/kg) and MY (21.5g/kg to 27.0g/kg). The differences between sires for these traits that indicate that there may be genetic variation present and provide preliminary evidence that selection on a methane production trait may be possible.

Ruminants contribute up to 80% of greenhouse gas (GHG) emissions from livestock, and enteric methane production by ruminants is the main source of these GHG emissions. Hence, reducing enteric methane production is essential in any GHG emissions reduction strategy in livestock. Data from 2 performance-recording research herds of Angus cattle were used to evaluate a number of methane measures that target methane production (MPR) independent of feed intake and to examine their phenotypic relationships with growth and body composition. The data comprised 777 young bulls and heifers that were fed a roughage diet (ME of 9 MJ/kg DM) at 1.2 times their maintenance energy requirements and measured for MP in open circuit respiration chambers for 48 h. Methane traits evaluated included DMI during the methane measurement period, MPR, and methane yield (MY; MPR/DMI), with means (±SD) of 6.2 ± 1.4 kg/d, 187 ± 38 L/d, and 30.4 ± 3.5 L/kg, respectively. Four forms of residual MPR (RMP), which is a measure of actual minus predicted MPR, were evaluated. For the first 3 forms, predicted MPR was calculated using published equations. For the fourth (RMPR), predicted MPR was obtained by regression of MPR on DMI. Growth traits evaluated were BW at birth, weaning (200 d of age), yearling age (400 d of age), and 600 d of age, with means (±SD) of 34 ± 4.6, 238 ± 37, 357 ± 45, and 471 ± 53 kg, respectively. Body composition traits included ultrasound measures (600 d of age) of rib fat, rump fat, and eye muscle area, with means (±SD) of 3.8 ± 2.6 mm, 5.4 ± 3.8 mm, and 61 ± 7.7 cm2, respectively. Methane production was positively correlated (r ± SE) with DMI (0.65 ± 0.02), MY (0.72 ± 0.02), the RMP traits (r from 0.65 to 0.79), the growth traits (r from 0.19 to 0.57), and the body composition traits (r from 0.13 to 0.29). Methane yield was, however, not correlated (r ± SE) with DMI (-0.02 ± 0.04) as well as the growth (r from -0.03 to 0.11) and body composition (r from 0.01 to 0.06) traits. All the RMP traits were strongly correlated to MY (r from 0.82 to 0.95). These results indicate that reducing MPR per se can have a negative impact on growth and body composition of cattle. Reducing MY, however, will likely have the effect of reducing MPR without impacting productivity. Where a ratio trait is undesirable, as in animal breeding, any of the RMP traits can be used instead of MY. However, where independence from DMI is desired, RMPR should be a trait worth considering.

In Australia emissions from the livestock industries represent 10.9% of the net national greenhouse gas (GHG) emissions in 2006, and most of these were from sheep and cattle. With the government signalling its commitment to reduce emissions, industries need to develop emissions reduction strategies. This paper identifies some of the current genetic improvement practices in beef cattle that reduce GHG emissions and also identifies new areas for further research with potential for GHG reductions. Current GHG emission reduction strategies in beef cattle are reliant on improving productivity of cattle in order to reduce emissions per unit of product. Hence emissions reduction at the national level is largely reliant on there being a cap or reduction in animal numbers. In the long term it is important that strategies that directly reduce GHG emissions per unit of feed intake be developed.