My wife has a large mix breed rabbit that stays in a pen with a tray on the bottom. I noticed today that it has blood inn the urine. What could cause this? He always has plenty of water and he spends all day in the yard munching on grass nd clover as long as it isn't raining. When it starts to get dark, I put him back and give him some rabbit food and a little bit of Timothy hay. Other than the blood he seems healthy.