South Wales Police are urging walkers living in rural areas who are using the countryside on their doorstep to take their daily exercise to stick to public footpaths.
The plea comes as farmers report seeing a rise in the number of people walking on their land with dogs let off their lead.
The main concern for farmers is for their sheep which are especially vulnerable at this time of year due to the start of lambing season.
Dogs being let of their leads can chase the pregnant sheep and the mere stress of a chase from a dog can result in a pregnant sheep losing its lamb.
Even well behaved dogs have also been known to attack sheep causing serious injury or death.
PCSO Rhodri Mason said: “In recent weeks we have had reports of sheep and other livestock being attacked by dogs on the hills of Pontarddulais and the surrounding rural area.
“It is a very worrying time for farmers and we would urge everyone to please be sensible and keep your dogs on leads when around farm animals.
“It is important to remember that those who let their dogs loose on farm land at this time of year face the real prospect of their dog being killed, as farmers are legally entitled to shoot a dog if it is threatening the welfare of their livestock.
“Please, be mindful when you take your run or walk, don’t trespass – use public footpaths, and always keep your dog on a lead.”