Last Updated on February 23, 2022 by Allison Price
Q: My Quarter Horse mare of 11 years has been healthy. However, I noticed that lately he seems to be more active in urinating than usual. Although I don’t see him emptying his bladder as often, I notice that I am removing more of his bedding from his stall. This is something that should be considered? The rest of his life seems normal.
A: The excessive urination condition is known as polyuria (PU). A horse suffering from PU must also have polydipsia, which is an increased intake of water. PU/PD may be caused by a problem in diet, behavior or disease.
The kidneys remove waste products from blood and filter them out of urine. The kidneys regulate the amount of water in the body, producing urine that is more concentrated than blood (deep-yellow urine) or less dilute than blood. Clear urine looks almost like water. The kidneys absorb more than 99 percent of blood water and allow for excretion at a 100-fold or greater concentration of nitrogenous waste products in urine.The kidneys filter out waste products from blood and remove them in the urine.
A small decrease in the kidney tubules’ reabsorption can lead to a significant increase in daily urine production. If the daily urine volume drops from 99 percent to 98%, it can lead to a dry stall.
A newborn foal that drinks mom’s milk is the best example of how diet influences urine output. A foal consumes five times the amount of water that an adult horse does on a per-pound basis. A healthy foal will wake up after a nap and drink a few glasses of milk before producing a clear, very dilute stream 10-12 times per day. A mature horse who eats all-hay may have to void concentrated (deeply yellow) urine up to three times per day.
Horses can have a lower urine output depending on the type of hay they are fed. A legume hay, such as clover or alfalfa, is richer in calcium and protein than grass hay and is easier to digest. Horses who are fed alfalfa have a higher urine volume and less manure piles. Stalls for horses that have been fed alfalfa are more wet than those that were raised on grass hay.
To answer your question, you should have your horse evaluated for early chronic kidney disease (CKD). This is a condition in which the kidneys no longer produce concentrated urine. Your veterinarian should first collect a blood sample from your horse to determine the concentrations of creatinine and urea nitrogen. These are waste products that can increase in CKD patients. To evaluate the size of the kidneys and any changes in appearance, kidney ultrasonography may be done if bloodwork indicates early CKD. CKD is a progressive disease. A good diet is important to keep the body in good health. Horses are not suited for kidney transplants or dialysis.
If your blood tests are normal, you can withhold water overnight to see if your horse is able to produce more concentrated urine without mild dehydration. This test can be done by placing a plastic milk container upside down with the bottom cut and padding to collect urine samples at the beginning and end of the water deprivation.
Psychogenic polydipsia is a condition in which your horse drinks excessive amounts of water. This behavior is often caused by boredom when horses are kept in stalls for long periods of time. This could be solved by increasing turnout and limiting the amount of water in the stall to just two five-gallon buckets per day, which is twice the daily requirement for horses. Psychogenic polydipsia usually disappears within a few weeks of these management changes.
Even if your horse has normal blood values, CKD could be suspected if he produces more concentrated urine after water deprivation. The management would be similar to the one described above. Early CKD is best managed with non-steroidal anti-inflammatory drugs such as flunixin meglumine, Banamine, and phenylbutazone (“bute”) that can worsen kidney dama