New to backyard chickens. One of our chickens came out the coop fine this morning. But wife found it on its back 2 hours latter not breathing. Nothing new to diet or yard. Rescued baby chicks from a pet store after Easter this past spring. Learning as we go. Any thoughts on preveting other chickens from same fate. The 2 yellow chicks turned white but got huge fast. This is one of the ones that passed today. Pet store knew nothing about type of chickens that they were. In researching online it is apparently common for bigger birds to suffer heart attacks? Any insights?