Cheilanthes sieberi
Small fern up to 50cm high. Stiff erect fronds elongated, triangular in outline, 2-5cm wide, dark green on upper surface, paler underneath and divided into small segments. Stipes are thin, dark brown to black, glossy and grooved on the upper surface.
Other ferns.
Native to New Zealand. Widely distributed, mainly in dry situations especially amongst rocks in North and South Islands especially central volcanic region of North Island.
Contains ptaquiloside, a carcinogen that also depresses haematopoiesis, and thiaminase, a poisonous enzyme present in some ferns which inactivates Vitamin B1. It is primarily toxic to cattle but also more rarely sheep, pigs and horses. Clinically, haematologically and pathologically indistinguishable from bracken poisoning (ptaquiloside). Throughout the year but mainly April to September.
Cattle and less commonly sheep, goats, pigs and horses.
Animals show weakness and staggering. When driven animals may become paralysed with heads bent back and death follows. In cattle deaths occur over a period of weeks and up to three weeks after removal from the fern. In sheep death can occur within three days of grazing the fern. Warning signs are staggering, drooling saliva, dyspnoea, loss of coordination, hyper excitability and sometimes epistaxis, heads outstretched and inconstant scouring sometimes with malaena.
Multiple subcutaneous, intramuscular and subserosal haemorrhages. Haemorrhage in lungs, myocardium and lower intestinal tract with ulceration over Peyers patches. Thin watery blood and black contents in the large intestine due to malaena.
Clinical signs, post mortem findings, as well as the animal having access to the plant.
Other plants that cause CNS signs eg bracken and ryegrass staggers. Other thiaminase and ptaquiloside containing plants eg bracken.
Horses and pigs - give thiamine daily (0.25-0.5 mg/kg iv or im). Prognosis is good if treated early. As with bracken ingestion, in ruminants early treatment is essential. Blood transfusions (4-5 litres) may be necessary and antibiotic therapy if secondary bacterial infections are present. Symptomatic treatment is indicated.
Avoid grazing areas infested with Cheilanthes to the stage where all other edible plants have been eaten out. Avoid stress eg driving, yarding for at least three weeks after stock have been removed from infested pasture.
Conner H.E. The Poisonous Plants In New Zealand. 1992. GP Publications Ltd, Wellington
Parton K, Bruere A.N. and Chambers J.P. Veterinary Clinical Toxicology, 2nd ed. 2001. Veterinary Continuing Education Publication No. 208
13 October, 2008