Susan Keller says river floodwaters can contain anthrax spores and can expose spores that are present in the soil. She says that can increase the risk of anthrax on pasture and range land.

Animals that aren't vaccinated often die quickly after being exposed to anthrax bacteria. Animals that are vaccinated rarely die.

Keller also is encouraging ranchers to monitor their herds for unexpected deaths and report them immediately to their veterinarians.

North Dakota usually has a few anthrax cases every year. In 2005, there was a bad outbreak, with about 1,000 animals dying. They included cattle, bison, horses, sheep, llamas and farmed deer and elk.