Anthrax has killed a third of a bison herd in southern Saskatchewan, provincial officials confirmed Tuesday.

As of Friday, 30 bison from the 90-animal herd at a Weyburn-area farm were dead, officials said.

Greg Douglas, the chief veterinary officer with the agriculture ministry, is warning livestock producers to consider vaccinating their herds against the disease. While anthrax is rarely a problem for humans, it can be deadly for animals.

"What we see is sudden-death loss," Douglas said.

"The animals are absolutely normal-looking and two hours later they're dead. They don't give any warning, it's not a situation where an animal will be off feed or just won't be right for a while. They are fine one moment and they are dead the next."

The cost of vaccinating is much less than the cost of replacing an animal, Douglas said.

Following widespread flooding in May and June, conditions are ideal for the anthrax spores that are naturally present in prairie soil to infect more animals this year, he said.

"As the animals start to chew off the grass in … low-lying areas that could have been flooded, they're going to be exposed to anthrax spores," he said.

"If they have no immunity then we could end up with more anthrax cases through August and September."

The worst year for anthrax in Saskatchewan was 2006, when more than 800 cattle and bison died.