Usually tearing the ass off means doing something very difficult.
Talking about chicken, eggs, and colorful sayings as Jay put it reminds me of this dialogue:Two chicken were having a talk around a barn corner and bragging about their eggs. The first said my eggs are sold at 45 cents a piece, the other laughed and said mine are bigger and are priced at 50 cents. The First sneered and barked that she wont be tearing her ass off for 5 cents.Usually tearing the ass off means doing something very difficult.