CALDWELL, Idaho (AP) — Fourteen stock and guard dogs in southwestern Idaho have been poisoned and 12 have died as a result of the same type of chemical.

The Capital Press reports that the Canyon County dogs have all been sickened by strychnine, which is often used to kill gophers and other rodents. The most recent dog died Monday, adding to the string of deaths that started in early April.

A veterinarian who inspected three of the dogs says they all had green dyed grain in their stomachs, which appeared to be gopher bait that contained strychnine. The vet says it is likely the poisonings were intentional.

All of the dogs were owned by Casey Echevarria and used to guard and shepherd sheep and goats.