Increasing the proportion of <i>Leucaena leucocephala</i> in hay-fed beef steers reduces methane yield

Context Leucaena leucocephala (leucaena) is a leguminous shrub adapted to higher rainfall (>600mm) in frost-free areas of Australia. It can be a source of high-quality forage for cattle grazing tropical grass-based pastures that are seasonally deficient in the nitrogen content required for adequate levels of performance. Leucaena contains bioactive compounds that may reduce methanogenesis in the rumen, helping to achieve Australia's goal to make red meat production carbon neutral by 2030. Aim A study was undertaken to evaluate the response in animal performance and methane production to increasing percentages of leucaena in a hay-based diet. Methods Growing steers were fed diets containing 0%, 18%, 36% and 48% leucaena. Intake, liveweight gain, methane production and yield were measured in a cross-over trial with two modern cultivars of leucaena (Redlands and Wondergraze). Methane was measured in open-circuit respiration chambers. Key results There were no effects of cultivar on most parameters. Increasing leucaena percentage in the diet increased dry matter intake, animal performance and methane production (g/day) but reduced methane yield (g/kg dry matter intake) according to the equation: methane yield=19.8&#x2212;0.09&#xd7;leucaena percentage in the diet. The inclusion of polyethylene glycol to nullify potential antimethanogenic activity of tannins restored methane yield by 67%, indicating that tannins were responsible for most of the observed reduction in methane yield. Conclusion The results demonstrate that leucaena can improve animal performance and reduce methane yield in steers fed low-quality grasses. Implications Leucaena can be included in diets of grazing cattle in areas agronomically suited to its production, as a means to reduce enteric methane emissions.