Bracken Fern is found throughout the world in open pasture and woodland. It’s one of the top 10 most toxic plants for horses in the United States.
Bracken fern has broad, triangular fronds that grow up directly from stout, black, horizontal root stalks and is the only fern that develops side branches. It’s bright green in the spring and in late summer the leaves turn golden and then brown, never completely dying but in this “dead stage” through the winter until new shoots come up the next spring where the old growth is. These new young shoots are single un-branched stalks with fronds coming off the stem at intervals. The very top, the fiddlehead, is curled up and will gradually unroll as it grows to approximately 2 to 4 feet high. Bracken Fern prefers moist, acidic soils and reproduces by spores produced on the back of the fronds. Young shoots are relatively palatable in early growth stages. Both fresh and dried bracken fern are toxic if ingested. Some horses will develop a taste for bracken fern and seek it out in the pasture and hay.
Bracken Fern contains ptalquiloside, a carcinogen. It also contains a type I thiaminase enzyme that degrades or destroys thiamine (Vitamin B1) and creates a thiamine analog (fake thiamine) that interferes with nerve function and other bodily processes.
The primary problem with low thiamine in horses is the development of neurological disease. Signs of neurologic dysfunction include depression, blindness, gait abnormalities, muscle twitching, in-coordination tremors and seizures. Your horse may also show signs of weight loss, a weak, fast pulse and lethargy. Death will occur in several days to a week.
Horses must consume quite large amounts of bracken fern for days to weeks before signs will develop. If the plant composes 20 to 25 percent of their diet, signs develop in about three weeks. If it composes 100 percent of their diet, signs occur in seven to 10 days.
If you suspect your horse has ingested Bracken Fern or is showing any signs of neurological dysfunction call your Equine Veterinarian immediately.
Prognosis is generally very good if treatment is begun before neurological problems develop. The onset of seizures and blindness is associated with a poor prognosis.
The best treatment is prevention. Remove all Bracken Fern from where horses are kept. Your local Ag Extension should be able to help guide you on how to identify and eliminate Bracken Fern and other toxic plants in your grazing areas. Do not overgraze pastures and make sure your horses have sufficient healthy forage available at all times in infested areas. Do not feed hay contaminated with bracken fern.
Once your horse is through the crisis and been cleared by the vet for the next stage of recovery, you may want to consider Massage therapy as a unique way to improve your horse’s overall health and well-being. Massage stimulates circulation to bring nourishment to tissues, speeds healing, boosts the immune system, improves digestion, reduces physical and mental tension, and releases endorphins that reduce pain and leave your horse with a sense of well-being.
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