Natural Variation in Methane Emissions among Progeny of Angus Bulls
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.