I've got 21 cornish x and I noticed this morning that only one of them has yellow feet, the rest are kind of a light brown, is this an issue?
Chicken feet color
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Pretty sure it's not an issue, unless the birds look drastically different otherwise. In other words, just make sure that they are all meat chickens.
My cornish X's from Townline have legs that range from white to yellow. Plus, one of my Buff Orpingtons has yellow legs, and they're supposed to be white!
Anyway, don't worry about their feet. It's very likely just a natural variation.