This is a really common question that we hear every year during winter in the Midwest! People usually notice red, orange or brown spots in the snow and ice where their horses have urinated. Normal horse urine can change color after standing for a while. This is due to the presence of plant metabolites (pyrocatechines) in the urine that change color when mixed with oxygen. When they oxidize they turn a red or orange color. It can happen year round (the same process can turn stall shavings red), but is especially obvious against the white snow!
Normal horse urine appears colorless, yellow or even cloudy yellow as it is voided. The color and cloudiness change as the bladder is fully emptied. If the urine appears a red, brown or orange color as it is being passed that can indicate a significant problem. Things that change the color of the urine before it is passed include blood, the breakdown of blood cells and the breakdown of muscle cells.
If you notice your horse urinating an abnormal color, call for an exam right away! If your horse is passing yellow urine that is turning red in the snow, you can breathe easy – that is normal!