I have a 3 year old California White chicken that has always been healthy up to this point. I found her hunched in the corner of the coop a month ago and with past experiences, I knew right away something was wrong. I brought her into the basement to isolate her and could feel immediately that she had sour crop. I was able to purge the contents out by dipping her head down and gently massaging her crop while holding her over the sink. I have had good success with this in the past with other chickens. I hold food and water for 24hrs until I am certain her crop is empty. Then start introducing small amounts of scrambled eggs with meal worms twice a day along with providing water with either apple cider vinegar have even tried water with copper sulfate. Each time I am able to get her back to health within a few days on that diet. I then slowly start introducing her normal food into the eggs and mealworms and have no issues until she starts getting 100% normal food. Then the sour crop immediately comes back. It will not come back with any ratio of eggs or meal worms in the mix, its only when she is on 100% normal food. I've even tried switching food with no avail. This has been going on for over a month now. I am now wondering at this point if she has developed some kind of food allergy? Any help would be greatly appreciated.