Many years ago a flock of greylag strayed too close to me. Their leader was nearly all white. Anxious to keep the strain pure I selected it as the one to go for. I managed a clean kill, and was really pleased with myself, until I went to cook it. The farmer said they crossed with his farmyard geese 20 years before, and I thoroughly believe it. I could not get a chainsaw to cut it, let alone a knife.