We have 50 Cornish x-rock chicks. This is our first time raising these. I also have 25 RIRs which we've raised in the past successfully. I'm using the same bedding for both and the x-rocks brooder box is plenty big enough for them but for some reason only the x-rocks are losing their feathers on their chest. It almost looks like they've been laying or rubbing against something rough. The x-rocks are outside in a building with a heat lamp to keep them warm and they are spread out, some under the light, some not so I don't think they are too cold or too hot. I am feeding them higher protein feed than what I'm feeding the RIRs. What could be causing them to lose their chest/stomach feathers? Also, since they grow a lot faster than RIRs can I drop the temp of their brooder box a little quicker than say the recommended for normal chicks?