http://www.extension.umn.edu/distribution/livestocksystems/DI5567.html
http://www.canr.msu.edu/vanburen/aghoarya.htm
Hoary Alyssum: Toxicity to Horses,
Forage Quality, and Control
R. L. Becker, N. P. Martin and M. J. Murphy
The possible toxicity of hoary alyssum (Berteroa incana) to horses has recently become an issue of local concern. The following summarizes the current knowledge and recommendations concerning this issue.
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Clinical Signs and Toxicity
The toxicity of hoary alyssum to any species of animal has not previously been reported. Therefore, our current understanding is based on field reports and recent feeding studies. No cases of hoary alyssum toxicity in ruminants (dairy, beef, sheep or goats) have been reported to date. Some horses, however, have shown a response to hoary alyssum.
Clinical signs
Horses experience depression and a "stocking up," or swelling of the lower legs, 12 to 24 hours following ingestion of hoary alyssum in hay or on pasture. A fever and occasionally short term diarrhea have also been observed. These clinical signs normally subside 2 to 4 days following removal of the alyssum source. In more severe cases, an apparent founder with a stiffness of joints and reluctance of the animal to move has been observed. Recovery of animals with clinical evidence of founder may take several additional days.
In very rare cases, where hoary alyssum comprised extremely high percentages of the hay (30 to 70%), circumstantial evidence exists associating the plant with the death of a few horses. To date, death has not occurred in horses fed hay containing hoary alyssum under experimental conditions.
Toxicity
Definitive statements about the toxicity of hoary alyssum when eaten by horses are difficult to make, considering the fact that many horses do not appear to be affected by it.
In field cases where a large number of horses were known to be involved, only approximately 50% of the animals ingesting hay containing 30 to 70% hoary alyssum demonstrated any of the clinical signs of toxicity. The cases of severe "stocking up," apparent founder, and death have only been observed in horses ingesting hay containing 30 to 70% hoary alyssum. Only mild "stocking up" has been observed in horses on pasture or those ingesting hay with low percentages of alyssum.
