I have had three birds with impacted crops this year...all of them cockerels. What causes a chicken to get an impacted crop? Is there anything I can do to keep this from happening to my chickens. Just so you know, two of them died already and the third is on his last legs. It is very discouraging, as these are all purebreds and they do not seem to have the same ability to fight off infections as my barnyard chickens.