There are lots of bad reasons why a horses urine is red. It can mean there is blood present, breakdown products from muscle, or even due to toxicity. However, one very common reason is due to a pigment called pyrocatechin.
Pyrocatechin is a break down product of plants and is commonly found in horse urine. When a horse urinates the pyrocatechin present in the urine contacts oxygen in the air and it turns red or orange in colour.
The staining is commonly seen on white hair on the back legs of mares, or sometimes clients report noticing the concrete pad at a tie up has turned red the next day.
If you see a horse urinating and it’s is a different colour to yellow then this is abnormal. However, if you see urine on the floor or urine staining on the hair coat change colour after a time period, then this is just due to science and nothing to worry about.