Pteridium aquilinum (king fern, eagle fern); Pteris aquilina. Pteridium ferns belongs to the family POLYPODIACEA. Large, dark green, pinnate leaves grow up from a rhizome. Fixed spore cases form a brown line underside of the pinnules of the leaves, ripening to release thousands of small round spores. Common in woods and on heaths and moorlands mainly on light acid soils and often the dominant flora in these areas.
Animals most affected
Cattle, (sheep, horses).
Ingestion of the green plant, during periods of food shortage, or when dried plant material is mixed in with hay or straw. Ingestion over a prolonged period (15 - 30 days) causes toxicity. Poisoning is frequent in areas where the fern grows naturally. Bracken poisoning is termed pteridism.
Drying the plant does not reduce its toxicity. Toxic doses not fully known, however large quantities of the plant need to be eaten continuously to cause toxicity. (The effects upon the bone marrow appear to be cumulative, though they have been reported after ingestion of bracken by ruminants over a short period.)
Important note: The latent period between ingestion of bracken and the appearance of symptoms is generally long, from several weeks to several months:
The clinical signs of bracken poisoning have a characteristic pattern of presentation:
These latter symptoms are often absent or minimal in particular breeds of cattle (e.g. Charolais).
Disturbances of nerve function associated with thiamin (vitamin B1) deficiency:
Lesions indicative of a general haemorrhagic syndrome:
No treatment found to be fully effective:
|for calves||0.4 1|
|for adult cattle||1-4 1 administered with 3% sodium citrate, 100 ml for every 400 ml blood;|
Antidote: thiamin (vitamin B1), 100 mg/day im.