I don't think there are any studies specifically on chickens, tuna and mercury content, or if the mercury which is in the canned tuna goes into the egg or stays in the chicken. Because there is no info, I'd use the same guidelines as I do for my kids, not more than one can a month, but my kids are bigger than chickens, so I'd feed them a little less. Heck, feed them flounder or cod instead, it's safer. . .