Yes, we've found this true also. So...can we infer from this that something about concentrated FM genes may be bad for their health? If so...I sort of compare it to breeding dogs that can only deliver puppies surgically (English Bulldogs) and cats that frankly can't breathe normally (some Persian types). We want birds that meet a standard we have created, but I myself would far rather have chicks that hatch with white wingtips and are vigorous, than solid black ones that never make it out of the egg, or die within days. I'm just saying. If crossing bloodlines creates more vigor (I wouldn't know - still looking for a roo of a different bloodline), then the more of that, the better.