CASE NOTES

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A large-scale poisoning event in cattle caused by Cape Tulip

Daniel Reiner, Willunga Veterinary Services, Mount Compass, SA, Julie Wayne, Gribbles VETLAB and Jeremy Rogers, PIRSA, SA

Introduction

Both one-leafed cape tulip (Moraea flaccida) and two-leaf cape tulip (Moraea miniate) are serious pasture weeds in WA, SA and Victoria. All parts of cape tulip contain toxic levels of cardiac glycosides of the bufadienolide type, with cattle being the most affected species.¹ Additionally, the plant is difficult to manage as it reproduces through both corms and seeds. Corms are the underground storage organ that provides resistance to unfavourable weather conditions and makes identification of the plant difficult.²

A producer in the Fleurieu Peninsula of SA lost over 100 of 200 cattle that had been grazing in a neighbour's 'bush block' during stormy weather in June. The cattle, due to calve in a few weeks in good body condition, were poisoned by cape tulip.

History

A group of approximately 200 springer cows six weeks off calving and of mixed ages were moved into a neighbour's paddock, as severe weather was expected. This block had bush and shelter but poor grass availability and a large amount of mature bracken fern. The block had been grazed each year, but in summer to manage fire risk. On Saturday 24th June, four days after moving cattle to this block, the owner found approximately 30 dead cattle and on Sunday 25th June approximately another 30 dead. The dead cattle appeared to have epistaxis. Prior to death affected cows walked slowly before collapsing and dying, and looked very uncomfortable and in pain.

Necropsy findings

Necropsy was performed on two dead cows. Findings included myoglobinuria, excessive rumen fluid, severe small intestine and abomasum inflammation with dark blood, haemorrhagic kidney and lungs, cardiomegaly and hepatomegaly.

Further autopsies were performed on Monday 26th June and the suspected diagnosis at this point was cape tulip (Moraea sp.) poisoning.

Although rumen contents were closely examined no plant material that resembled cape tulip was seen. There were large stands of cape tulip in the bush block area, on swampy land, and there was evidence of grazing by cattle. It was noted that cattle had also been chewing on the bark of trees in the same location. Most dead cattle appeared to have died without struggling, many had aborted and most were found dead amongst the trees/shrub, rather than in the cape-tulip-infested area.

It was estimated that more than 100 cows died in this event.

Subsequent action

Bracken fern poisoning was suspected initially. The remaining cattle were immediately moved out of the bush block onto adjacent paddocks. Deaths continued after the remaining cattle were relocated to adjacent paddocks. Some became recumbent and were treated for metabolic conditions, but most did not respond to treatment.

Laboratory findings

Cape tulip poisoning was confirmed from characteristic post-mortem changes that typically affect heart muscle and abomasum. Serum pepsinogen (an indicator of abomasum damage) was very high. Salmonella spp. were not detected in tests and an Anthrax ICT conducted on one cow was negative.

Histopathology revealed moderate multifocal to coalescing acute myocardial degeneration, segmental acute small intestinal mucosal haemorrhage and moderate multifocal lymphocytic abomasitis. The main finding was within the myocardium. In these sections, lesions were widespread but subtle.

Multifocal myocardial degeneration is described in cases of cape tulip poisoning and may cause death by affecting conductivity throughout the heart. Cardiac lesions such as these can also cause death by cardiac arrhythmia. This finding is a non-specific but well recognised in cases of poisoning by plants containing cardiac glycosides, including cape tulip.

Other possible causes included nutritional deficiencies (potentially copper, but unlikely with this history) and other toxins including 1080 or plants containing fluoroacetate. Changes in liver and kidney were non-specific but suggestive of sublethal toxic cellular injury. In the kidney, there was likely myoglobulinuric nephrosis.

Figure 1. Thickening and haemorrhage in large bowel

Figure 2. Severe inflammation of the abomasum in a freshly dead cow

Figure 3. A dense sward of Cape tulip and grass

Figure 4. A freshly dead cow that aborted

Figure 5. Multiple cows found dead in shrub paddock

Figure 6. Multiple cows found dead in shrub paddock

Discussion

This tragic event occurred as an inadvertent consequence of hungry cattle exposed to a very toxic plant previously unknown to the owner. It is not unusual for producers to be unaware of the dangers of cape tulip as livestock raised in areas that have it rarely ingest it. In this case, hungry cattle in late-stage pregnancy were moved into a sheltered area that contained some large stands of cape tulip, and limited available good quality pasture.

Rapidly removing the cattle from exposure to this plant undoubtably saved many lives in this case. As little as 1 kg of cape tulip can kill adult cattle and the time until death is dose dependent. Some poisoned cattle will survive but develop diarrhoea - presumably because of gut irritation. The toxin that is a cardiac glycoside (bufadienolide) acts on heart muscle and produces nausea, blurred vision, dizziness and diarrhoea.³ The post-mortem changes described in this case; haemorrhage in heart muscle, gut irritation, particularly fourth stomach and large bowel, were typical of cape tulip poisoning.

Affected cattle have a very inflamed abomasum and die rapidly, often without struggling. Due to the amount of inflammation present, toxicity is likely to be very painful.

Unfortunately, there is no treatment, and eradicating the plant can be difficult. Table 1 (below) describes the lifecycle and strategy for control of the plant. In this infestation, no flowers were visible, but the plants tend not to flower until 2-3 years old.⁴ The plants observed were between 300-400mm high, with no flowers, so they could have been immature plants.

Table 1. Cape tulip calendar

References

1. One-leaf Cape tulip: declared pest WA Agriculture and Food, 2020
2. Cape tulip - how and when to control Landscape South Australia & PIRSA
3. Poisonous plants of Australia Selwyn Everest, Revised edition (1981)
4. Cape Tulip - what you should know WA Department of Agriculture factsheet2023.html">2023 Conference