Well, I stated that my ISA Brown could be a bit aggressive towards the other birds in the flock. But they are all the same age and can take of themselves. I think I would get rid of any bird that went out of its way to kill chicks. But I don't have a mixed aged flock. Too bad the ISA Brown is aggressive towards other birds, because it is by far the most people friendly hen in my flock.I think they're fine layers but because of their aggresion I will never buy more of them. My production blues lay just as well and actually lay bigger eggs and they are so docile and friendly. One of my ISA browns not only was attacking the other hens but went on a mission to kill the new chicks and started attacking me. She was gone real quick.
I'll have to check out your Production Blue suggestion. I never heard of them. We have Production Red listed as available locally. Would they be similar only different colored?
FWIW, last week I talked to a lady that has 60 hens. She sells eggs. She told me that her next flock was going to be all ISA Browns because she had the best luck with them in terms of egg production and hardiness for our area (northern Minnesota). Our biggest concern for our birds is how well they handle our harsh winters. Some breeds may be great egg layers, but if they cannot handle our cold and die off in the winter, then other options need to be considered.