01/24/2025
❄️🩸Reddish Brown Urine in the Snow – Is my horse ok!?
I remember the first winter I began working with horses - I walked out into the snowy pasture to catch my horse but was taken aback when I saw blood in the snow! I immediately began following these pools of blood around the pasture in an attempt to find which horse was injured. It wasn’t until I noticed a pattern, or really a lack thereof, that I realized it wasn’t blood and everybody was fine (I was also young and clearly didn't know what blood should look like 😂). But I was confused, what caused these red, orange, or brown stains in the snow. After watching for awhile, I realized it was their urine that came out as a normal color, but it would change colors in the snow. And as an inquisitive soul, I was bound and determined to get to the bottom of why this happened and I am certain I was not the only one!
Well, it turns out the color change observed in the urine is caused by a plant metabolite known as pyrocatechines. When this metabolite is oxidized (exposed to air), it loses electrons which can lead to a change in the chemical structure and consequently, the color. This is a similar process to what we see when iron rusts. Iron is exposed to air and moisture and is oxidized to form iron oxide, commonly known as rust. Copper can also go through a similar process in which the shiny and metallic copper can become a green patina (think the Statue of Liberty).
While this process happens year-round for horse urine, it tends to be more noticeable in contrast to the white snow. These colors in oxidized urine are acceptable, however, if urine is red or brown when it is passed, that is reason for concern. Red and brown urine may indicate concerns with the urinary tract, liver, or muscles, and often necessitate veterinary attention. However, if the urine is a colorless to tan or yellow color when it leaves the body, colored urine in the snow is not a concern.
What did you think the first time you saw red or brown stained snow? Did anyone get as freaked out as me?
Cheers!
Dr. DeBoer