The SSPCA is investigating reports of poison being left in a field at a north Bute farm.
Strathclyde Police were contacted after a dog belonging to the tenants of Lower Ettrick farm, near Ettrick Bay, fell ill and was taken to a Rothesay vet for treatment.
There it was found the dog had eaten fresh meat which had been contaminated by blue pellets, thought to be either slug or rat poison.
Several more pieces of similarly contaminated meat were found in the vicinity, while a local horse owner, who rents one of the Lower Ettrick fields, discovered several piles of the blue pellets near where she keeps her horse.
Police brought the matter to the attention of the SSPCA, who have greater expertise in the area of animal poisoning and who also have the power to submit reports to the procurator fiscal.
Enquiries into the matter are continuing; in the meantime, anyone with information about those responsible can contact Strathclyde Police on (01700) 894000 and ask for Rothesay police office.