Differences in the nutrient concentrations, in vitro methanogenic potential and other fermentative traits of tropical grasses and legumes for beef production systems in northern Australia.

BACKGROUND

In northern Australia, beef cattle grazed extensively on tropical rangelands are responsible for 5% of the nation's total greenhouse gas emissions. Methane (CH ) is a potent greenhouse gas and in grazing ruminants might be mitigated by selecting forages that, when consumed, produce less CH when fermented by rumen microbes. This study examined variability in the in vitro fermentation patterns, including CH production of selected tropical grasses and legumes, to identify candidates for CH mitigation in grazing livestock in northern Australia.

RESULTS

Nutritive values and fermentation parameters varied between plant species and across seasons. Grasses with a relatively low methanogenic potential were Urochloa mosambicensis (wet summer), Bothriochloa decipiens (autumn), Sorghum plumosum (winter) and Andropogon gayanus (spring), while the legumes were Calliandra calothyrsus (wet summer and autumn), Stylosanthes scabra (winter) and Desmanthus leptophyllus (spring). There was some correlation between CH production and overall fermentation (volatile fatty acid concentrations) in grasses (R = 0.67), but not in legumes (R = 0.01) and there were multiple plants that had lower CH not associated with reduction in microbial activity.

CONCLUSION

Differences in nutrient concentrations of tropical grasses and legumes may provide opportunities for productive grazing on these pastures, while offering some CH mitigation options in the context of northern Australian extensive beef farming systems. © 2017 Society of Chemical Industry.