Bracken fern (Pteridium esculentum) is a native perennial fern found worldwide including most temperate areas of Australia. In New South Wales it is distributed along the coast and throughout the tablelands and slopes. Bracken fern causes two distinct diseases in cattle: an acute haemorrhagic syndrome associated with leukopaenia, thrombocytopaenia and anaemia; and a syndrome of multiple urinary bladder tumours known as bovine enzootic haematuria .
This report describes a case of bovine enzootic haematuria (BEH).
A producer in the Cowra area purchased an eight-year-old Angus cow from the Central Tablelands Livestock Exchange at Carcoar in June 2016. The cow calved at the saleyard and delivered a live bull calf. A 5:1 vaccination and benzimidazole drench was administered on arrival in accordance with standard farm protocols. Blood was observed in the urine soon after calving but appeared to resolve. Over the next 11 weeks the producer observed profuse, watery diarrhoea and estimated the cow had lost 150kg body weight despite a good appetite. No response to an ivermectin backline or combined antibiotic and non-steroidal anti-inflammatory treatment was observed, and the cow became progressively weaker. The producer consulted Central Tablelands Local Land Services concerned about the possibility of bovine Johne’s disease.
The cow attempted to stand when approached but immediately collapsed to sternal recumbency. Her BCS was 1.5/5. She had moderately sunken eyes and prolonged skin tenting, and her temperature was 38.4°C. She was tachypnoeic and tachycardic, mucous membranes were pink, and capillary refill time was approximately 2 seconds. She had profuse, watery greenish black diarrhoea; no abnormalities were detected on vaginal or rectal examination.
Blood was collected for a ruminant general biochemistry profile, pestivirus antigen capture ELISA (PACE), liver fluke ELISA and BJD ELISA. Faeces were sent to the State Veterinary Diagnostic Laboratory (SVDL) and held for further testing pending preliminary results.
The cow died 24 hours after initial examination and before test results were available for any of the requested diagnostics.
The urinary bladder was markedly distended with dark red urine (Figure 1). A firm, raised, dark reddish purple mass with an ulcerated surface measuring 60mm diameter was present in the neck region (Figure 2). An adjacent area of the bladder wall was markedly haemorrhagic and thickened (Figure 2).
The kidneys were white with multifocal, brown, circular, depressed, well-demarcated lesions ranging from 2-20mm diameter. These lesions were wedge-shaped on cut section consistent with renal infarction (Figure 3).
The uterus was non-gravid. White, circular, flat, plaque-like lesions measuring 2-3mm diameter were present on the mesometrial surface of the uterine horns.
The colon and rectum were filled with watery, greenish black faeces.
Significant findings of the ruminant general biochemistry profile are summarised in Table 1.
|Calcium (uncorrected)||1.84||2.0-3.0 mmol/L|
The cow was PACE, liver fluke ELISA and BJD ELISA negative.
Histological examination of the urinary bladder indicated the presence of at least two neoplasms, likely secondary to bracken fern toxicity. The thickened, haemorrhagic area of bladder wall was identified as a haemangiosarcoma. The urinary bladder mass was more difficult to classify. The SVDL considered a transitional cell carcinoma or metastasis from a uterine adenocarcinoma the most likely differentials. The latter could be possible if one of the plaque-like lesions visualised on the mesometrium progressed from dysplastic (primary uterine adenoma in situ) to neoplastic (uterine adenocarcinoma) and metastasised to distant sites. This hypothesis was not pursued with further laboratory testing.
Evidence of prior renal infarction from tumour emboli and chronic, diffuse interstitial fibrosis further supported the end-stage kidney disease detected on biochemistry. The submitted tissue sections also showed neoplastic cells in the renal medulla. This finding is reasonably common and often an incidental finding in older cattle. However in this case it was considered suggestive of a tubular carcinoma with different cell morphology to the urinary bladder mass.
The SVDL commented that it would be uncommon for one animal to have three distinct neoplastic processes occurring at once, but not impossible.
Whilst the grazing history of this cow was unknown, she originated from the Lithgow area where bracken fern is widely distributed. It is important to note that mulga or rock fern (Cheilanthes sieberi) is also capable of producing BEH in cattle in Australia .
Bracken fern contains ptaquiloside, which has proven carcinogenic properties. Although bracken fern is ubiquitous in temperate areas, BEH has a more localised occurrence that is most likely related to plant strain . A New Zealand study found that concentrations of ptaquiloside varied greatly between geographic areas and a high proportion of stands (63%) did not contain the toxic agent. A higher percentage of bracken ferns contained ptaquiloside (42%) in areas where BEH was known to occur compared to those areas where the disease is not recognised (6%) .
The toxicity of bracken fern varies with the stage of growth with newly sprouted young fronds being more toxic. The rhizomes that become exposed after cultivating bracken fern-infested pasture are considered the most palatable and dangerous part of the plant. There is no loss of toxicity when bracken fern is dried or unintentionally incorporated in hay .
Although cattle will usually only consume bracken fern when pasture is sparse, the ingestion of only relatively small amounts of the plant over prolonged periods of time is sufficient to cause BEH . Clinical disease is therefore often observed in mature animals as was the case in this 8-year-old cow.
A significant number of cattle affected by BEH develop multiple tumours within the same bladder as evidenced by the haemangiosarcoma and probable transitional cell carcinoma detected in this case. One study investigating BEH lesions found epithelial tumours alone in 51.2%, mesenchymal tumours alone in 17.4%, and both epithelial and mesenchymal tumours in the remaining 31.4% of affected bladders . Epithelial malignancies may invade locally and about 10% metastasise to the medial iliac lymph nodes or lungs .
The persistent haematuria that characterises BEH occurs due to the existence of haemorrhagic cystitis, bleeding urinary bladder tumours or a combination of these conditions. Although a full blood count was not performed in this case, a non-regenerative anaemia is often detected in affected animals. Normal leukocyte and platelet numbers are present. Recent studies indicate a monocytosis can be detected in 31% of younger animals in response to initial consumption of bracken fern. This finding may therefore act as an early haematological marker for BEH .
There is no effective treatment for BEH so preventing access to bracken fern is imperative, especially if pasture availability is poor. It is particularly important to avoid recently cultivated land where rhizomes have become exposed. Where limited areas are overgrown by bracken fern, producers may elect to fence off the stands. Spraying with herbicides, burning, ploughing and reseeding will reduce the degree of bracken fern infestation .