Bracken fern poisoning

From Cow
Bracken fern, commonly seen around farmlands
Pale mucous membranes associated with bracken toxicity
Vulval haemorrhage in a six-year old cow with suspected bracken fern poisoning
Haemorrhages in the mesentery of a six-year old cow with suspected bracken fern poisoning

Bracken fern (Pteridium aquilinum) is a common form of intoxication in cattle known as enzootic bovine haematuria.

Brack fern is an ornamental plant that cattle eat when normal food supplies are limited. Poisoning by this plant causes a variety of skin and circul[1].

Bracken fern toxicity occurs as a result of ingesting toxins contained within the plant. These toxins have been identified as three unstable norsesquiterpene glycosides: ptaquiloside, ptesculentoside, and caudatoside, in variable proportions[2]. The primary acute effect of these toxins is myelopthistic anaemia, retinal degeneration and thiamine deficiency[3].

Clinical signs

In mild cases of intoxication, acute dermatitis on the nasal bridge is a tell-tale sign.

In more severely affected cattle, two distinct syndromes may be seen; an acute haemorrhagic syndrome where bone marrow suppression leads to leukopaenia, thrombocytopaenia and anaemia and urinary tumours.

Presenting linical signs include dermatitis, anaemia, petechial hemorrhages, haematochezia, bright blindness and haematuria due to urinary tumours[4]. Severity of symptoms appear to be related to dose and duration (over many weeks) of exposure to the toxic glycosides. In chronic cases, cattle are often lethargic, inappetant and feverish.

Affected cattle often have delayed clotting time and bruise easily. This disease appears to be more fatal in young and weak cattle.

Long term exposure to bracken is usually carcinogenic to cattle, resulting in neoplasia of the pharynx, oesophagus, rumen and urinary bladder[5][6][7].

Diagnosis

Diagnosis is based on history of exposure to bracken, supported by presenting clinical signs and supportive blood tests which confirm a non-regenerative anaemia and markedly reduced platelet cell count.

On post-mortem of cattle which have died, the carcase is generally pale and blood clots poorly. There is usually widespread evidence of haemorrhage throughout the body.

Treatment

Treatment consists on limiting access by cattle to the offending plant.

Supportive medications such as broad-spectrum antibiotics and multivitamins may assist recovery.

In severely affected cattle, mortality is usually >90%. Measurement of the platelet count is recommended as it is the best prognostic indicator for poisoned animals[8].

Blood or even platelet transfusions may be appropriate but require large volumes (2–4 L blood) to effectively treat cattle.

References

  1. Vetter J (2009) A biological hazard of our age: bracken fern [Pteridium aquilinum (L.) Kuhn]--a review. Acta Vet Hung 57(1):183-196
  2. Fletcher MT et al (2011) Norsesquiterpene glycosides in bracken ferns (Pteridium esculentum and Pteridium aquilinum subsp. wightianum) from Eastern Australia: reassessed poisoning risk to animals. J Agric Food Chem 59(9):5133-5138
  3. Wilson D et al (1998) Should we be frightened of bracken? A review of the evidence. J Epidemiol Community Health 52(12):812-817
  4. Karimuribo ED et al (2008) Investigation of a syndrome characterised by passage of red urine in smallholder dairy cattle in East Usambara Mountains, Tanzania. J S Afr Vet Assoc 79(2):89-94
  5. Corteggio A et al (2011) Expression of gap junction protein connexin 43 in bovine urinary bladder tumours. J Comp Pathol 144(1):86-90
  6. Gava A et al (2002) Bracken fern (Pteridium aquilinum) poisoning in cattle in southern Brazil. Vet Hum Toxicol 44(6):362-365
  7. Marrero E et al (2001) Pteridium aquilinum (bracken fern) toxicity in cattle in the humid Chaco of Tarija, Bolivia. Vet Hum Toxicol 43(3):156-158
  8. Merck Vet Manual