If you feed kelp as a staple, your birds will hatch with their future leg color already strongly present, and old birds do not lose leg color. It's a complete vitamin and mineral supplement that is a powerful endocrine regulator. It will start old non layers laying again and put a stop to hens moulting until bare or losing feathers from mating. You don't get 'overmated' hens if they're kept on kelp, no matter how many roosters are around. It makes their feathers too strong and well attached to fall like autumn leaves just because another chook jumped on them.
But if you think you're breeding pure white chooks, or any purebreds, kelp will cause their actual phenotype to show. They can be a few years old already and perfectly true to the breed standard, but after being on kelp for about a year, will show you what they're really made of. I highly recommend all breeders at least test this, it's amazing. Birds look like a paler version of their true coloration when not on kelp.
I've had many examples of this but here's the strongest one, visually clearer because they were pure white to strt with. (Mostly I don't keep pure white anythings). I bought some 2-year-old hens which were raised on the susual pellets, which I then switched onto my diet which has kelp. They went from being pure white with white legs, very pale irises, pure white feathers, white beaks etc, to being mottled red and black, 'smutty' greyish reddish, and yellow legged, yellow beaked, orange eyed, etc. Their eggs went from white to brownish. Offspring before and after kelp was added to the diet are as different as night and day.
If these birds had never been fed kelp they would have died white as snow, and all offspring they produced with white males would also have remained white as snow, but it's deceptive. It's just the color they are when not on a complete diet. The feeds marketed as complete are often actually better described as 'survival rations' and are not as broad spectrum as they would need to be to provide true health to such a high degree.
