I have a 2 year old English orpingtons hen who is losing condition. She's always had a problem with a messy butt, but she has incredibly long feathers and fluff and I assumed that this was the reason. She is a really big bird, but she is losing weight now. They're all eating soaked organic whole grain feed (and have been for ages) and she seems to have an insatiable appetite. My daughter said she had a nasty burp yesterday. Is it sour crop, or something else? How can I tell?