Please ring,
some sheep dogs do kill sheep, some go next door to do so, he will want to know, it may not be a working dog,
oh and ring 101 and get them to log it, as the farmer may of reported lambs being killed, then they can add a description to log.
I was up walking across the fields very early one morning, checking for iced over water supply) a couple of years back, spotted a pair of dogs (labs)going for the sheep and lambs on the opposite hillside, by the time I and my dogs had got over there they had killed a couple lambs and injured a few, legged it as we arrived,
went on up to the farm the sheep belong to, informed them, phoned back to ours, by the time we(farmer and I) came back out all of five minutes later, one of his dogs arrived with a dead lamb, it had gone down and picked it up. my dogs don't chase sheep, unless you make them, but some do.
they spend a lot of time with them, but they will go and pick up a dead lamb and bring it to me,
so tell the farmer he needs to know what is going on, it could be anything,
It is amazing how many people let their dogs out to wander, mind you I've been stood in a field inspecting the sheep, and had people walk in and just let their dogs off, and look astonished when you go ape shit as their dogs attack the sheep.
I've had people tell me that because they are on a public footpath, their dogs are allowed to run free and attack livestock.
my mate who has sheep on the coast, each year she has lambs and sheep, chased off the cliffs, by people walking the coastal path, who when entering a part of the south west coastal path, which has open grazing, don't put their dogs on leads, usually because the they haven't trained the dog not to pull, so they can't be bothered.
A dog is only as good as it owner chooses to allow it to be.