My rabbits behind is getting "dirty" everyday?

ok.. i know lots about rabbits but my rabbit, Lilly, is getting "dirty" everyday
my parents said it happened to one of the rabbits before and they cutted down the hair on the behind area...
is this a good idea?
if you have any other ideas plz tell
Answers:
trimming the area is a very good idea.rabbit poop generaly wont leave the rabbits hiny dirty...feed only good quality food...

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Is it from urine or feces? Are you cleaning her cage and litter box every day?
If it's urine, take her to a vet. She might have a urine infection that is causing her pain, making her unable to keep the urine from getting on her fur when she pees.
If it's feces, what is her diet like? I'm assuming she has normal looking hard round bunny poops, not general diarrhea. Eliminate all treats. Do not feed pellets with treats in them, and make sure her pellets have at least 18% fiber, the more the better. Make sure she eats lots of grass hay, no alfalfa. If she's an adult and no longer growing, switch to low-protein timothy pellets such as Oxbow Bunny Basics/T or Kaytee Timothy Complete. Is she getting veggies, and which types? Maybe they are upsetting her stomach, especially if you are giving her things she is not used to. Always add new foods slowly so her stomach can adjust to them and to make sure she can tolerate them.
If this doesn't help, or if she has diarrhea (all poops are soft or runny) take her to a vet as she may have an infection or a parasite called coccidea.
Here is how to safely clean your rabbit's behind:
http://www.bio.miami.edu/hare/buttbath.h...