Leghorn chicks back pecked

[The ChickInn egg supply]

So I have 28 3 week old chicks and I’ve notice that as the white leghorns feathers have come in the chicks have pecked at them. So 4 of my white leghorns have bloody backs. I will attach a pic. What can I do to stop this and let the feathers grow back in?

 

[Poultrybonkers]

To crowded and lack of protien is why that happens