Investigating photosensitisation in livestock resulting from ingestion of the pasture legume Biserrula pelecinus L.

Biserrula pelecinus L. is an annual legume native to the southern Mediterranean. It was first introduced to Australia in 1991 as a potentially valuable rotational pasture species for livestock production. It produces large quantities of biomass, exhibits drought tolerance and is effective for weed suppression in pasture rotations. However, despite proving to be a valuable addition to the pasture toolbox, producers in NSW and WA have reported a limiting factor to uptake: incidence of severe photosensitization when grazing sheep on biserrula pastures. Biserrula photosensitivity, anecdotally, appears to be associated with non-senescent foliage and shows an increased severity of clinical signs in young animals grazing green tissues; however, the pathogenesis of this photosensitization and the metabolite(s) responsible are, as yet, unknown. Studies reported in this project have identified that both commercially available cultivars of biserrula, ‘Casbah’ and ‘Mauro’ can cause outbreaks of primary photosensitization. This work identified that fresh foliar extracts were photosensitizing, and that this activity diminished greatly with drying. Both cultivars were found to be equally bioactive, and photocytotoxic activity was associated with extracts from field-grown biserrula at all stages of plant growth until senescence. Biochemical analysis using fractionated extracts, bioactivity-guided metabolic profiling is described as an experimental approach.