Farmers in Otago and Southland are dealing with one of the worst outbreaks of salmonella hindmarsh in more than a decade. Veterinarians say hundreds of sheep have died.
The outbreak began in January and farmers are not sure why it has taken such a deadly turn.
The disease is present within the soil of all farms, but farmers do not usually vaccinate their animals against it.
It takes up to five days for infected sheep to show signs of the disease and once signs are apparent, they usually die within 48 hours.
Vet South veterinarian Donna Hamilton said farmers must begin a vaccination programme if the disease strikes. She said it's a particularly painful disease for livestock.