References
Bracken and horsetail poisoning
Abstract
Bracken (Pteridium spp.) and horsetail (Equisetum spp.) are ancient plants that contain thiaminase. Chronic grazing by monogastric animals, such as horses, results in an induced deficiency of thiamine (vitamin B1). This manifests as ataxia, lack of co-ordination (‘bracken staggers’), loss of condition and stumbling. As the disease progresses, there is weakness, inability to stand, muscle tremors, coma and convulsions. In addition, haemolytic anaemia and haemoglobinuria may occur. Diagnosis of bracken or horsetail toxicosis is based on clinical signs and history of exposure. Post-mortem findings are generally non-specific. Treatment is supportive with prompt removal of the plants, and provision of good quality forage and nursing care. Supplementation with thiamine can be effective. Prevention of poisoning involves ensuring adequate forage is available, and preventing access to the plants. Clearing the bracken or horsetail can be difficult and in the case of bracken, specialist advice should be sought.
Bracken and horsetail are both ancient plants that have long been recognised as poisonous, causing induced avitaminosis B1 in horses. This has multiple effects, as vitamin B1 (thiamine) is an essential vitamin involved in metabolism and in maintaining the myelin of peripheral nerves. This article discusses bracken and horsetail poisoning in horses.
Bracken (Pteridium spp., Figure 1) is a genus of ancient, large, coarse ferns. It is one of the worlds most abundant plants, growing throughout the world (except where it is very cold or very dry). It is found in woods, heaths, sand dunes, neglected pastures, hedgerows, moors and even in walls, and is often dominant over large areas, mainly on light, well-drained acid soils. It is found throughout Britain and Ireland, and is occasionally cultivated in gardens and parks. Bracken has large, highly divided leaves with rhizomes from which the fronds arise at intervals. In the past, the genus was commonly treated as a single species, Pteridium aquilinum, but it is now generally subdivided into about ten species.
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