One week after Grangeville rancher Ed Stuivenga began feeding oat silage to 86 newly weaned calves, the first three fell to the ground and refused to arise. "I blamed the silage right away," recalled Stuivenga, who took the calves off the feed.

Stuivenga figured the calves had succumbed to nitrate poisoning, but veterianarian Virgil Frei ruled that out and referred the case to Washington State University's School of Veterinary Medicine.

Over the next weeks, more cattle refused to eat or developed a staggering gait. "If you scared them, they tipped over," Stuivenga said.

University of Idaho veterinary toxicologist Patricia Talcott remembers attending a meeting of diagnosticians at WSU where the case was being discussed. No one at that point had suggested botulism, which is unusual in cattle, as the possible cause, but the case reminded Talcott and others of a recent botulism incident in Washington, also involving cattle fed silage.

"It seemed like a carbon copy of the previous case," she said.

Silage samples sent to the University of Pennsylvania confirmed the presence of Clostridium botulinum, the bacterium whose toxin causes paralysis of the smooth muscles.

Dick Heimsch, director of the Idaho Agricultural Experiment Station and a botulism specialist, explained that dormant spores of the bacterium are widespread in soil. Under moist, oxygen-free, and acid-neutral conditions, the otherwise harmless spores can come to life and produce their killing toxin.

Stuivenga's silage must have developed these favorable conditions. Normally, in a process akin to pickling, silage becomes too acidic to support the botulism bacteria. Likewise, pickled green beans rarely cause botulism, but those canned in water, if insufficiently treated with heat, provide ideal conditions for the bacteria to thrive.

Victims, human and bovine, face a discouraging prognosis, said Heimsch. "By the time you see the symptoms, it's really too late to do anything." Two months after Stuivenga's outbreak began, 14 cattle were dead. Jim Church, UI extension educator in Grangeville, has since held a meeting to inform local ranchers about the incident and the possible perils of silage.