A common question that always seems to come up in winter months is why a horse’s urine looks red. People usually notice red, orange or brown spots in the snow where their horses have urinated. Normal horse urine sometimes turns red or brown after standing for a while. This is due to the presence of plant metabolites called pyrocatechines. These oxidizing agents cause the urine to change color when mixed with oxygen. It can happen year round (the same process can turn stall shavings red), but it is especially obvious against the white snow.
Normal horse urine appears clear, yellow or cloudy yellow in color, and doesn’t turn red until after it is voided. The color and cloudiness change as the bladder is fully emptied. If the urine appears a red, orange or brown in color as it is being passed than it can indicate a problem. Things that cause a change in urine color before it is passed include whole blood, the breakdown of blood cells and/or the breakdown of muscle cells.
If an abnormal color of urine is observed while your horse is urinating, your veterinarian should examine the horse. If your horse is passing normal yellow colored urine, rest easy, as this is normal.