Prof. Megan Ryan1, Dr Gereltsetseg Enkhbat1, Dr Kevin Foster2, Dr Caitlin Wyrwoll1, Dr Tim Watts1
1The University of Western Australia, Perth, Australia, 2Department of Primary Industries and Regional Development, Perth, Australia
Biography:
Dr Megan Ryan has worked on a range of pasture-related projects since arriving at The University of Western Australia over 20 years ago. Recently Megan has been focussed on the ecology and breeding of annual pasture legumes, particularly subterranean clover.
Abstract:
Old cultivars or ecotypes of subterranean clover (Trifolium subterraneum) with concentrations of the isoflavone formononetin in leaves greater than 0.20% of dry weight may reduce fertility and cause other health issues in sheep. In long-term pastures, diverse populations of subterranean clover often develop. There is little knowledge about the isoflavone concentrations in the subclover ecotypes and cultivars present in such pastures. In this study, we investigated two permanent pastures on adjacent farms near Pingelly, Western Australia. Both pastures contained a mixture of self-regenerating subterranean clover, grasses and broad-leaved weeds. The pastures were grazed by sheep during the study. Pasture cages were installed, and pastures sampled within and outside the cages in early winter and late winter and shoot dry mass and botanical composition determined. Subterranean clover cultivars and ecotypes were grouped based on leaf marks and other morphological characters. The rod-point technique was used to assess the proportion of each cultivar/ecotype and leaf samples were assessed for the concentrations of formononetin, as well as for genistein, and biochanin A. The pastures contained a mixture of subterranean clover with high, medium and low formononetin concentrations. High concentrations of formononetin reached over 1% of dry weight. The isoflavone results suggested that cultivars and ecotypes were correctly grouped even though some could not be confidently identified. However, concentrations of formononetin, genistein and biochanin A sometimes varied greatly between sampling times and paddocks. We conclude that accurate prediction of livestock isoflavone intake and associated risk of infertility for pastures with a diverse population of subterranean clover will require comprehensive assessment of each paddock and can be influenced by the growing environment.