Read through all of these:
https://www.merckvetmanual.com/poultry?_gl=1*1f5hio7*_up*MQ..&gclid=CjwKCAiAxvGfBhB-EiwAMPakqsdd_MCNxWtiDzjkojUpBQUCxevGZYuOfOSFknQdY7z2JqLUa2R0vBoCgh8QAvD_BwE&gclsrc=aw.ds
Full not so squishy bellies can be internal layers or salpingitis. While reading pay close...