If you think you see blood in your horse's urine this winter, don't panic. Finding bloody-looking urine in the snow under your horse may send you racing to call the veterinarian, but chances are what you're seeing perfectly normal.
The red spots that you see are a result of your horse's urine reacting with the cold snow. Proteins in the urine, called pyrocatechines, oxidize in low temperatures, which produces colors ranging from a light pink to red, orange or brown. The same thing can occur when a sample of urine is refrigerated.
When in doubt, collect a fresh urine sample from your horse---a process that involves a large can duct-taped to a long stick and a lot of patience. If the collected sample isn't red, your horse is probably just fine.