Sarah nailed this one. A lot of high-strung PSDs (usually Mals...) get so spun out at work that they spin circles and repeatedly strike their tails against the car insert. They break the tail open and begin to bleed. Even if you bandage it or stop the bleeding, it is hard to keep the dog calm long enough to heal completely. What ends up happening is one injury being repeatedly opened. Amputation is often the final option in order to keep the dog healthy and able to work.