I think my girls got into a fight!!
Featured Stories on BackYard Chickens
I've had this happen before, so it isn't anything to worry about. Just stop the bleeding and maybe rub some antibiotics on it to prevent infection. Because her comb is already red, the other hens likely won't peck at the wound.
The causes for this in our flock include fighting (usually among roosters), a rooster trying to breed with a hen (he holds onto the comb with his beak) or burning their comb on a heat light during the winter.
If you don't have any roosters, then likely it was a fight. There are great ways to stop aggression in birds including more space or perches, places to hide, hidden treats or treats hung on string to distract them, and other such things.
Also, a predator may have been the cause of this. Watch for signs of aggression among the hens to see who is the one causing it and to determine that it wasn't anything trying to eat them.
I hope this helps and I hope she gets better soon.
Clean her up with some disinfectant (Vetericyn, Betadine, Peroxide, etc) and put some bluekote on to prevent the other hens from picking at the injury. She should recover just fine with that.
As far as preventing it in the future, how many hens do you have in how big of a space? Usually fighting is minimized with ample room for them to run away if they want. You could help them a bit by giving them places for individual hens to hide. If you can free range them for the whole day, that is best but I know it's not always feasible.
Fights happen in flocks no matter what you do so I wouldn't fret if this is just a one time occurrence. It becomes a problem if it happens on a regular basis. Then I would find the aggressor and separate her for a week to bring her down in the pecking order. Or, if they aren't pets, you could cull her so those aggressive traits aren't passed on...