Consider yourself lucky. My girl's beautiful, thick, touch-the-ground, black-and-white tail was ruined when she got it stuck in something and yanked the black part out from the roots on the tip of her dock. You got off easy. =]
I tried to keep up on trimming, so her tail wasn't constantly trying to nourish dead hair. I also used MTG and kept her tail in a bag. It seems to have helped.
A good diet helps. Also, use MTG, as it helps regenerate hair growth. I keep my horse's tail up during the winter so it doesn't get caught in anything, and you also must be diligent about keeping the tail clean and healthy.