Welsh Corgi x shedding his undercoat?

You should brush the dead hair out so the dog won't get matted. Double-coated dogs shed twice a year; spring and fall. Your dog may be losing the summer coat or it may be shedding in response to the longer hours of light and increased heat we artificially provide in our homes in the colder months, fooling the dog's system into thinking it is summer again. A good slicker type brush should do the job. Brush daily while the dog is shedding.