Sudden death of six heifers due to a hepatotoxin

Above: A map of the water square showing locations of cases and other findings of note​.

Case definition: Brahman-cross heifers found dead, no previous clinical signs, no signs of paddling or struggle. Cases within close proximity (eg 50 metres).

Disease mapping: At time of visit 3 were dead from of a mob of about 240 heifers in mid-late pregnancy (calving Oct-Jan). All had died in a gully within 50 meters of each other. One had died beside a very stagnant puddle of water. The other animals looked healthy. A paddock walk found the boundary paddock has a good cover of feed, about 30 cm high, clean water in the trough and tank, and green couch grass and 2-leaf/ 4-leaf stage seedlings growing around the waterway. A timeline was created showing stock movements, mustering and vaccinations, and dates of deaths.

Gross findings: A post mortem of a heifer was conducted at the first visit 16-24 hrs after death. Autolysis was evident in all organs. A full set of fresh and fixed samples taken. The list of differential diagnoses was Noogoora Burr, botulism, clostridial disease, urea, other plant toxicity, lead or arsenic (no access), anthrax (blood discharge from nose -highly unlikely). A fourth heifer, found dead four days after the farm visit, was examined within a few hours of death. Gross findings included jaundice of fatty tissue; ecchymosis and petechial haemorrhages on the omentum, rumen, lungs and heart; excessive fluid in abdominal, thoracic and pericardial spaces; thickened, oedematous omentum; small, even white spots on the liver; and infarction in the medullar of the kidney. A full set of fresh and fixed samples taken.

Laboratory findings: Samples from the first post mortem were too autolysed for examination. There was no evidence of anthrax in spleen or liver, or cyanobacteria (blue-green algae) in the water sample. Liver lesions in the second animal were consistent with hepatotoxins of plant origin including green cestrum (Cestrum parqui), poison peach (Trema tomentosa), the cotyledonary stages of Xanthium species (Noogoora burr and Bathurst burr) to name a few.

Animal / management / environment risk factors: A final diagnosis of Noogoora burr toxicity was made. The clinic had seen cases in the area many years ago.

Recommendations: The owner was advised to fence off the green areas and gully with water to eliminate exposure to potential toxin (stock were unable to be moved because of feed requirements). In the longer-term, managers should be aware that this paddock produces Noogoora burr and control appropriately.

Above: (1) Haemorrhages were evident in multiple organs; (2) Young seedlings were growing in the waterway.