I would eliminate as much of the weed as you can. For ruminants, bracken fern will cause bruising, excessive bleeding, causing anemia and possibility of death.
From Purdue University Vet hospital:
In ruminants: Bleeding disorders (bruising, hemorrhaging, anemia), breathing difficulties, weight loss, death
However, other toxins in bracken affect ruminants, most notably ptaquiloside, a lactone toxin that affects the bone marrow. The toxin is present in all parts of the plant, but is concentrated in the rhizomes, and is toxic in fresh as well as dried plants. Consumption of bracken results in the depression of bone marrow (and thus red and white blood cell and platelet production), and the plant has a direct or indirect anti-coagulant property. Cattle show signs after grazing bracken for 1 to 2 months, although death may occur within this time frame as well. Affected cattle have an increased temperature, weight loss, and exhibit increased bruising and bleeding. From the excessive bleeding, cattle are anemic, and can die within a week of showing signs. Young cattle may develop swelling in the larynx and have difficulty breathing. Sheep may be poisoned in a similar manner, but are apparently more reluctant to consume bracken.
For ruminants: Immediately remove cattle from bracken pastures, or fence off the bracken areas to limit access. Do not feed hay or bed animals on straw that contains bracken. A veterinarian can assist with treatment of affected animals, but this may be cost prohibitive. Evacuation of the rumen and intestinal tract is usually not of value, since the poison accumulates in the system for many days, and there may be little or no toxin remaining in the digestive tract to be removed once clinical signs appear. Treatment is concerned with alleviating the clinical signs and providing supportive care. Blood transfusions may be attempted, but the prognosis is poor for clinically affected animals.
SAFETY IN PREPARED FEEDS: Bracken remains toxic when dry, and is never safe for consumption.
PREVENTION: Grazing animals should not be allowed access to bracken fern, especially if they have developed a taste for it.
Here is a link to the whole article:
http://www.vet.purdue.edu/depts/addl/toxic/plant23.htm
Keep your goaties healthy - get rid of toxins they may be tempted to ingest.
