A longitudinal study of methane emissions by cattle grazing buffel grass or buffel grass/Desmanthus pastures.

Context. Reducing methane emissions from grazing cattle is important to reduce the environmental impact of Australia’s beef industry. Aim. A 16-month grazing study was completed on a commercial property in central Queensland, to determine the animal production and methane emission response to including Desmanthus in buffel grass (Cenchrus ciliaris) pastures. Methods. There were two treatments (Control (~ 95% buffel grass) and Desmanthus (~ 70% buffel grass/30% Desmanthus). A group of 400 tropical composite yearling heifers were divided according to LW to four 300 ha paddocks. Of these, 98 self-selected to use in-field methane monitoring units throughout the study. Pastures were evaluated for biomass and botanical composition, and cattle were weighed and sampled for faeces every 2 to 4 months. Pasture and faecal samples were analysed for nutritive value by near infrared analysis. Spatial variation in pasture and animal activity was observed using global positioning system (GPS) technology. The data were analysed as a 2 x 3 factorial with two treatments assessed over three seasons, wet season 1 (15/12/2023 to 16/04/2024), dry season (16/04/2024 to 09/10/2024) and wet season 2 (09/10/2024 to 30/04/2025). Key results. Overall Desmanthus tended to increase LW gain (P = 0.05) and increased hot half carcase weight (P < 0.01). When season was included in the analysis there were treatment by season interactions for LW gain (P < 0.01), and methane production (g/head.d), yield (g/kg DM intake) and intensity ( g/kg LW; P < 0.05). In wet seasons Desmanthus increased LW gain (P < 0.1) and reduced methane yield (g/kg DM intake), and intensity (g/kg LW) by 8 and 9%, respectively (P < 0.05), whereas in the dry season there was no treatment effect. There was a treatment by season interaction for diet nutritive value and the percentage of non-grass (predominantly Desmanthus; P < 0.001). Conclusion. It was concluded that the response in animal performance and methane emissions was due to the presence of Desmanthus in the diet of cattle in the wet seasons. Implications. The inclusion of legumes such as Desmanthus in tropical pastures is an available option to reduce methane emissions from grazing cattle.