Dealing with plant poisoning of livestock: the challenge in Queensland

Poisonous Plants of the Genus Pimelea: A Menace for the Australian Livestock Industry

Pimelea is a genus of about 140 plant species, some of which are well-known for causing animal poisoning resulting in significant economic losses to the Australian livestock industry. The main poisonous species/subspecies include Pimelea simplex (subsp. simplex and subsp. continua), P. trichostachya and P. elongata (generally referred to as Pimelea). These plants contain a diterpenoid orthoester toxin, called simplexin. Pimelea poisoning is known to cause the death of cattle (Bos taurus and B. indicus) or weaken surviving animals. Pimelea species are well-adapted native plants, and their diaspores (single seeded fruits) possess variable degrees of dormancy. Hence, the diaspores do not generally germinate in the same recruitment event, which makes management difficult, necessitating the development of integrated management strategies based on infestation circumstances (e.g., size and density). For example, the integration of herbicides with physical control techniques, competitive pasture establishment and tactical grazing could be effective in some situations. However, such options have not been widely adopted at the field level to mitigate ongoing management challenges. This systematic review provides a valuable synthesis of the current knowledge on the biology, ecology, and management of poisonous Pimelea species with a focus on the Australian livestock industry while identifying potential avenues for future research.

A review on Pimelea poisoning of livestock

Pimelea poisoning of cattle, historically known as St. George Disease or Marree Disease, is a prevailing issue in arid grazing regions of inland Australia. Ingestion of the toxic native Pimelea species that contain the secondary metabolite simplexin, a diterpene orthoester with potent protein kinase C activity, induces diarrhoea, characteristic oedema and potentially fatal right-sided heart failure in cattle. Outbreaks of toxic Pimelea in the grazing field depend on seasonal prevalence. However, all stages of the plant carry the toxin, from seeds, juvenile plants to dead plant material. Livestock generally avoid consuming green Pimelea plants and only consume toxic Pimelea when pasture is minimal or where Pimelea growing through grass tussocks results in inadvertent ingestion. Our knowledge base of Pimelea poisoning has greatly improved with past research, yet the health hazards for livestock grazing in Pimelea affected pastures remains a significant issue whilst the ongoing search to develop effective strategies to mitigate poisoning continues. The goal of this review is to collate historical and recent research giving an overview of the current understandings of Pimelea poisoning, the toxin, its toxic effects and progress made towards remedies to alleviate the effects of Pimelea intoxication.