Investigating livestock production with the pasture legume Biserrula pelecinus: aetiology and pathogenesis of photosensitivity.

Biserrula pelecinus if a legume recently introduced to Australia as a sustainable pasture legume species, with the ability to thrive in Mediterranean climates. Biserrula has been implicated as a cause of sporadic and unexplained photosensitivity in livestock grazing Biserrula pastures. To maximize the utility of Biserrula as a pasture plant, more needs to be understood about the induced photosensitivity syndrome. This study explored epidemiological and pathological factors of affected animals. A farmer survey was used to establish the context for this study. To validate results, modern laboratory techniques were used to establish hematological and biochemistry reference intervals for mixed breed weaned lambs. An on-farm case series of photosensitized animals grazing biserrula cv. Cashbah was conducted followed by an experimental photosensitivity trial. on two proportions of biserrula cv 'Mauro' (50% and 100%) as well as a subclover control group. From the survey, most affected livestock are sheep, despite cattle occassionaly grazing the pasture. Reference intervals were similar to previously published values. There were no consistent and clinically relevant remarkable haematological or biochemical findings in biserrula photosensitized sheep on either Casbah or Mauro cultivars. Histologically, the only consistent, clinically relevant abnormalities were epithelial defects. importantly, there was no indication of hepatocyte injury or death. These results add furher evidencet that the toxin(s) involved in biserrula photosensitivity are primary toxins that occur sporadically in the plant, and do not interfere with liver function in the animal. This study provides important foundations to build upon with further research aiming to identify the toxic principle.