A Dairy UP research project, in collaboration with University of Sydney and NSW Department of Primary Industries and Regional Development (DPIRD), is investigating how Kikuyu grass (Cenchrus clandestinus) becomes toxic to help develop safe grazing management practices for dairy farmers.
Project lead, NSW DPIRD Plant Biosecurity R&D manager, Krista Plett, said providing clarity around Kikuyu toxicity aims to support dairy farmers so they can avoid rare cases of Kikuyu poisoning, which can cause cattle deaths and illness following heavy rainfall after prolonged dry conditions.
"Ultimately, project findings could be used to develop new Kikuyu varieties that are less susceptible to toxicity, diagnostic tests to evaluate pasture safety, in-field preventative treatments and treatments for affected cattle," Dr Plett said.
"Research has identified seven compounds consistently at high levels in toxic leaf and stem samples, yet at low levels or absent in the baseline samples.
"Five fungi were more abundant in the toxic samples, with two fungal species now under investigation as potential causes of Kikuyu toxicity."
Kikuyu is a perennial pasture species adapted to warm or hot conditions and commonly grown in NSW for livestock production. It is fast growing and produces more high-quality dry matter than other C4 grass varieties.
The research team collected and analysed grass and soil samples from properties across NSW and visited farms affected by suspected Kikuyu poisoning from 2018 to 2019, and in March and April 2024.
Samples were collected from reference and affected farms and analysed for fungal and bacterial communities.
Metabolomics, a technology which can identify the fingerprint of compounds within a sample, was used to identify potentially toxic compounds by comparing baseline samples with those from affected farms.
University of Sydney PhD student, Vivien Tan, ran a greenhouse trial to create the environmental conditions that are understood to precede Kikuyu toxicity, including drought and wet conditions.
Ms Tan examined the response of three genotypes, or varieties, of Kikuyu, which were inoculated with soil and their associated microorganisms collected from farms with a history of toxicity.
The fungal community composition, or microbiome, was significantly impacted after re-watering, suggesting the microbiome is more responsive to extreme wet conditions than dry conditions.
There was little to no detectable influence of genotype or control versus drought treatments on the overall fungal community composition.
DPIRD veterinary research officer, Barbara Brito Rodriguez said Kikuyu toxicity was rare, yet the risk of poisoning from the grass could deter dairy farmers and beef cattle producers from unlocking all its benefits.
"Understanding the underlying reason for Kikuyu poisoning would inform ways to address the risks and enable farmers to manage their herds and pastures with increased confidence," Dr Brito Rodriguez said.
"Giving farmers more assurance and confidence in using Kikuyu pasture would potentially deliver more year-round feed options for their livestock."
