For rabbit constipation there is a solution but you MUST be careful. Lettuce in large amounts can give rabbits diarrhea which may lead to death. However, if you are careful to give your rabbit a small amount of fresh lettuce (NOT ICEBERG) every day or so along with it's everyday fresh mixed greens, your bun should be back to normal in no time. But again, please be careful. Their systems are so delicate.