Figure 1. Bracken in a fern and is one of the world's most abundant plants. It produces lush green growth, a) Courtesy of Elizabeth Dauncey), but is also toxic when dried (b).

Bracken and horsetail poisoning

As stated, poisoning only occurs after ingestion of bracken for several weeks (Hadwen and Bruce, 1917); with horsetail, clinical signs occur after grazing for 2-5 weeks (younger, growing animals...