In late June 2021 a farmer from southwest Sydney contacted the District Veterinarian to report the sudden death of a yearling heifer that had been moved from a nearby property with 11 other heifers just two weeks prior to the incident. Two months prior to moving the animals the owner excavated a small dam on the property to facilitate access to water for the livestock. Cattle were grazing mixed native pasture (Danthonia, Microlaena, Red grass etc). Annual vaccination and drenching status were up to date.
On arrival at the property the carcase appeared bloated and bloody discharge was oozing from the anus and nostril. Given the history and appearance of the carcase an anthrax immunochromatographic (ICT) test was performed, which was negative. Anthrax was considered as an unlikely differential diagnosis as the property is situated outside of the Anthrax belt. A necropsy examination was performed and samples (fresh and fixed) for laboratory examination were collected from most of the internal organs. The major post-mortem findings were severe ulceration on the abomasal wall with signs of internal bleeding and epicardial haemorrhages. Given the postmortem lesions, cardiac glycoside toxicosis was added to the differentials. A paddock walk revealed a large number of Mother of Millions (Bryophyllum spp.) plants next to the dam. There was evidence that the plants had been eaten by the cattle.
Histopathology revealed a subacute cardiomyopathy, acute periacinar hepatic necrosis and severe abomasal mucosal haemorrhages. Heart muscle damage and gastrointestinal irritation are primary effects of cardiac glycosides, with periacinar hepatic necrosis occurring secondary to heart failure-related hypoxia. Following a discussion with the pathologist a diagnosis of cardiac glycoside toxicity was made. The source of the cardiac glycoside was flowering Bryophyllum spp. (Mother of Millions).
Bryophyllum spp. are serious weeds introduced from Africa that grow on the coast and north-west slopes and plains of NSW. The plant flowers between May and October (depending on species) when most intoxications occur as the flower heads are more toxic than leaves and stems (McKenzie, 2012). There is usually a mucoid, black, moderate diarrhoea. Sudden death on moving due to a cardiac episode is commonly reported. Affected cattle are often staggering, perhaps due to low blood pressure. Cattle can die up to three weeks post removal (two weeks mostly) due to the rumen becoming atonic and then functioning again as toxin wears off. Gastrointestinal ulcers are seen, especially in the abomasum and on the leaves of the omasum. Ulcers on the omasal pillars into the abomasum are considered pathognomonic.
Microscopic lesions can vary depending on the species of the plant involved (composition of toxins varies between Bryophyllum spp.), amount of toxic plant material eaten, and time period of ingestion, amongst other factors. Effects on the heart are considered the most important (McKenzie et al. 1986), however histological lesions may not be seen in all cases (Reppas, 1994). Affected animals may die very acutely before damage to myofibres becomes histologically evident. The lesions can be localised and can be missed if only limited heart tissue is available for examination. In an incident reported in the Greater Sydney area in 1994, cattle were fed four wheelbarrow loads of flowering Bryophyllum pinnatum plant material, most of which was eaten by two cattle, leaving only thick stems and roots. The cattle died within 48 hours. A severe rumenitis was the most significant histopathological lesion, but no heart lesions were seen in the sample of interventricular septum submitted (Reppas ,1994).
Naïve cattle are attracted to the flowers of Bryophyllum spp., but not the plant. Pastures that have been seriously overgrazed or overstocked can predispose livestock to eating anything they can, especially if they are hungry. Several factors can lead to livestock becoming poisoned from eating toxic plants. In this case several contributing factors were suspected, including newly introduced young cattle that may not be familiar with the plant and dry pasture with a lack of palatability. Producers should evaluate their pastures to determine if adequate pasture is present before introducing livestock onto the paddock. If there is a lack of adequate pasture, livestock may be more likely to eat poisonous plants.