Unexplained deaths of 10 weaner cattle from a mob of 70 over 4-6 weeks.
Time and location: The Pilbara, Sep-Oct 2018.
Case definition: 12-month old weaner cattle with gradual weight loss and inappetence, then weakness, collapse and death.
Gross post mortem findings: Two post mortems were conducted five days apart. The first was by the producer (using one of the producer kits!) and the second under the supervision of a field veterinary officer and local practitioner.
The producer noted a prominent gall bladder, soft kidneys full of fluid, and a large amount of black watery contents in the rumen. He sent fixed sections of lung, liver, heart, kidney and reticulum to the laboratory. At the second post mortem they found a large amount of fluid and some grass/hay in the rumen, an empty large intestine and rectum, yellow-tinged omentum, pale lungs and kidneys, a friable liver and urine the colour of water.
Fresh and fixed lung, liver, heart, kidney, rumen, intestine and brain samples were sent, as well as blood, urine, rumen contents, vitreous and samples of an unusual green plant that the owner had seen the cattle eating.
Laboratory findings: Both animals had nephrosis and histopathological changes in the liver:
- The first had mild patchy interstitial fibrosis of the kidney with distension and sloughing of epithelial cells in the renal tubules, and mild, multifocal hepatocellular necrosis.
- The second had moderate, multifocal renal tubular necrosis, this time with visible oxalate crystals in the lesions, and mild, multifocal, subacute periacinar lipidosis of the liver. The blood chemistry was consistent with renal compromise (increases in phosphorous, urea and creatinine). The hepatic lipidosis fits with fat mobilisation after a period of starvation or inappetence.
The oxalate crystals seen in the second animal could be responsible for the nephrotoxicity OR secondary to kidney damage.
The plant sample was identified as Clerodendrum tomentosum, a shrub/small tree that occurs in areas across the north and is also commonly known as the hairy lolly bush or downy chance (to name a few). An oxalate assay on the plant sample revealed very low levels of oxalate and is thought unlikely to cause oxalate nephrosis. However the plant had been associated with cattle deaths previously but the toxin unidentified (Ross McKenzie).
Animal / management / environment risk factors: Both animals were part of a mob of 12-month old weaners who had not been in this paddock before. The paddock had been previously used for adult cattle only.
Recommendations to the producer: As both of the autopsied animals had kidney damage most likely caused by plant poisoning, the owners were advised to search the paddock for unusual plants. The pathologists listed a number of common plants that have been known to cause nephrotoxicity (such as Lesser Loosestrife, scarlet pimpernel, lamb poison and a couple of types of amaranth).
Obtaining a definitive diagnosis of plant poisoning can be challenging
The key bases to cover for diagnosis are:
- A very thorough disease mapping – to establish where animals have been, where the cases have occurred over time, with a case definition that builds to accurately describe the clinical syndrome and animals at risk
- Confirm and describe pathology in affected animals
- Shortlist the suspect plants and their stage of growth – CSIRO has great Australian reference for this is by Ross McKenzie in 2012
- Send the lab photos of the plants and the environment and good plant specimens (with all the bits) for accurate identification and further testing if indicated.