Plant-associated metabolites and ruminant toxicity in south eastern Australia

Submission note: I, Elizabeth Read, submit this thesis as a total fulfilment of my requirements for the award of Doctor of Philosophy to the School of Applied Systems Biology, College of Science, Health, and Engineering, La Trobe University, Victoria.

Thesis with publications.

Plants and their associated microbial communities are a major source of poisonings for both humans and animals. The most common type of toxins are low molecular weight secondary metabolites that usually need to be ingested to cause toxicity. In grazing systems these toxins can have a profound effect on the health and production efficiency of livestock grazing on natural or supplemented pastures. This thesis comprises three case studies of different plant-associated poisonings of ruminants. The first study investigates suspected poisoning of cattle fed pomegranates (Punica granatum L.) as a supplement during limited feed availability. Pomegranates are a known source of punicalagin, a tannin, which was found to be cytotoxic to bovine kidney cells at high doses. However, degradation of punicalagin results in gallic acid, which was shown to be significantly more cytotoxic than punicalagin. The second case study involves outbreaks of phalaris toxicity. Phalaris grass (Phalaris aquatica) was investigated for the presence of key alkaloids that are thought to be associated with toxicity. The concentration of these alkaloids was determined throughout a growing season and related back to the amount present during outbreaks of toxicity on-farm. There was no clear association with alkaloid concentration and environmental factors, thus the stimuli for production of alkaloids in phalaris grass is likely complex. However, toxicity is generally associated with new phalaris growth when livestock are particularly hungry. The third study focused on a reoccurring toxicity, acute bovine liver disease (ABLD). The cause of ABLD has not been identified and is currently diagnosed by liver histology. Several metabolites were found that could indicate the presence of a toxin in liver and urine from affected animals. Additionally, there were a number of endogenous metabolites that could be used to provide clues about the possible biochemical effects of toxicity. Moreover, there were several metabolites found in seed heads of rough dog’s tail (Cynosurus echinatus) that are significantly up or down regulated during periods of ABLD toxicity. The common factor in these poisonings is that they are all associated with reduced or limited feed availability, or the overabundance of a single food source. Therefore, this thesis concludes with a discussion of strategies to manage and minimise plant-associated poisonings from pasture by increasing the diversity of feed available.