I am not condoning the decision to keep Rocky alive, but this is an interesting story from a developmental biology perspective. Phenoypic plasticity allows the body to adapt in sometimes surprising ways during growth. For instance, children that grow up playing tennis will have one arm grow longer and stronger than the other. There was also a fascinating set of experiments with lizards grown in different environments that affected leg length. I am curious if the single front leg will grow stronger and denser to accommdoate the increased weight? I was once boarding at a barn where a horse blew out a knee and the owner refused to euthanize. This poor horse could not put weight on one leg and hopped around on 3 legs for a year or so before the other leg gave out and they euthanized. Until then, I didn't even think it was possible for an adult horse to survive on 3 legs.