We started see red urine in a new gelding. What is causing this?
Horses often have quite a bit of sediment and occasionally some dark pigment in their urine. In addition, a dehydrated horse will produce very concentrated urine, resulting in a darker looking fluid (and often a stronger smell), a common situation in the wintertime due to reduce voluntary intake. Even perfectly normal, well-hydrated horses can produce very dark urine, particularly during the end of the stream when voiding the “dregs” at the bottom of the bladder.
This is usually not an indication of serious problems, but occasionally very dark urine can be a signal of health issues. Muscle damage, typically tying-up, releases pigment called myoglobin into the bloodstream that is subsequently filtered by the kidney and excreted in urine. Excessive levels of myoglobin will cause the urine to look like Coke and can cause serious damage to the kidney, which is why we will put a severely affected horse on IV fluids to help dilute and flush out this toxin. Blood in the urine, from trauma, infection, kidney/bladders stones, or invasive tumours can also appear quite dark. Even components of normal coloured urine will metabolize into a dark rusty coloured substance after voiding, which can look like blood when they pee on something light coloured like snow. This phenomenon causes lots of phone calls to the vet the day after a good snowfall.
If your horse seems healthy and normal otherwise, I would keep an eye on things but not worry too much. If you have any suspicion of a health problem, a physical exam with bloodwork and urinalysis can determine the source of the unusual colouring.
Melissa McKee DVM