Police are investigating the incident after it was discovered that the dog had died from an banned pesticide.
They are warning that humans out walking in the Tanat Valley could be at risk if they come into contact with the pesticide and say they think birds of prey are being targeted.
The incident happened in May with the dog dying within minutes. Laboratory tests just published have revealed that the animal had been poisoned by a substance called Aldicarb.
Evidence showed that the dog had ingested the remains of a black feathered bird, which was suspected of having the poison on it.
Sergeant Matthew Howells, a Wildlife Crime Liaison Officer for Dyfed Powys Police, is concerned that someone in the community is targeting wildlife and setting down poison baits with an aim to kill birds of prey.
"In March 2013, NEAT had a similar report of poisoning when another local resident saw a dead Red Kite on a footpath in the area. Post mortem results from that incident also tested positive for Aldicarb. Although this incident happened 12 months ago and was about a mile away, we believe that these two incidents are connected and that someone in the area is targeting wildlife, in particular birds of prey," he said.
"However, the indiscriminate nature of such a poison and its illegal use poses a significant risk of death to other creatures. Also there is an increased risk of the pesticide coming into contact with humans. The Tanat valley in this area is very attractive for local residents to walk their dogs. Children and their parents on such walks are also at risk of serious illness should they come into contact with the substance."
"In the interest of safety if anyone comes across any dead birds or other wildlife in the countryside then do not touch them but contact the police if you suspect foul play."
The police are asking that should anyone have old stocks of the pesticide on their farms to please contact their farming union and seek advice on the safe disposal of it.
Anyone who has information on any person who has access to this substance or where and how it is being used illegally is asked to contact Dyfed Powys Police on 101 and ask for the information to be passed on to Sergeant Howells or alternatively contact Crime Stoppers anonymously on 0800 555 111.