Moldy corn may have killed five horses and four foals last year, according to a UC Davis veterinarian. Samples of corn and mixed feed revealed high levels of a fungus-produced toxin called fumonisins B-1, says Frank Galey, assistant professor of clinical toxicology at the UC Davis-based California Veterinary Diagnostic Laboratory Systems. Affected horses exhibit disorientation, delirium, head-pressing and other central nervous system abnormalities about seven days after exposure to the toxin, and death often resulted, Galey reports. The most definitive diagnostic evidence of moldy corn poisoning is destruction of the white matter in the brains of the poisoned horses. Some may also have liver tissue that has been destroyed. Although difficult to prevent, the incidence of moldy corn poisoning can be decreased by not feeding damaged corn or corn screenings to horses, says Galey. He notes that swine are also affected by fumonisin, but ruminants are thought to be less sensitive.