Pet mince from the butchers are basically just left over offcuts/offal/internal organs all minced up together, so that's why they smell a bit funny, they also add sausage mince to the mix, all of these combined can often cause dogs to have a permanently upset tummy from the different mixture ratio of each meat. Butchers also throw in a bit of garlic to mask the smell of sometimes a bit 'off' meat.

I never buy pet mince from the butchers, have tried various butchers over the years on emergency occasions that my usual beef orders ran late and I was out of meat for my dogs, however got sick of the same cr*ppy stuff they tried to sell cheap and called it pet mince. I would rather buy fresh chicken mince than pet mince from butchers.