The racehorse's extraordinary peeing power.

Previously published Slate articles made new.
April 30 2010 7:04 AM

How Much Do Racehorses Pee?

Horses really do possess great powers of urination.

See a Magnum Photos gallery of horses.

Twenty horses are scheduled to compete in Saturday's Kentucky Derby. The question everyone is dying to have answered before the Run for the Roses: How much are those racehorses going to pee? Thankfully, Slate's Explainer tackled this question back in 2007. The original piece is reprinted below.

Illustration by Mark Alan Stamaty.

The third leg of horse racing's Triple Crown takes place on Saturday, with the running of the Belmont Stakes. Around 60,000 fans will be watching in Elmont, N.Y., as they put down beer and the track's signature cocktails. Needless to say, they'll probably be peeing as much as the racehorses. Wait, how much does a racehorse pee?

Advertisement

A lot. Horses typically produce several quarts of urine every four hours, for a total of about 1.5 to 2 gallons per day. (By contrast, an adult male human pees 1 or 2 quarts per day.) The stream, usually one-third to a half-inch in diameter, can last up to 30 seconds. In general, the larger the animal, the more it pees. A Clydesdale, for example, weighs twice as much as a Thoroughbred and produces urine in greater volume (and with a more pungent smell). An average pasture horse that spends its day grazing might also beat a racehorse in a peeing match: Pasture grass contains a lot more water than the carefully prepared grains and pellets fed to racehorses.

The popular notion of incontinent racehorses seems to have roots in the late 1970s, when trainers began the widespread use of diuretics like Lasix (furosemide). Lasix inhibits the absorption of sodium and draws water into the bladder. This causes the horse to excrete more fluids, which could, in theory, make a horse lighter on its feet and faster on the track. Depending on the dose, a Lasix treatment could cause a horse to move several gallons of urine within an hour, which could translate to a quick drop of 10 pounds from a horse's body weight before a race.

It's not against the rules to dose a racehorse with Lasix, but its use is carefully regulated and abuse will result in a penalty. (In general, you're only allowed to use the drug to prevent internal bleeding during a race. You're not supposed to use it strictly as a diuretic.) Racing officials have run drug tests on competitors since 1903, and today they take blood and urine samples before every race. At the Kentucky Derby and most other major races, competitors using Lasix are allowed to compete, but they're marked with an L on the programs.

Got a question about today's news? Ask the Explainer.

Explainer thanks Sue McDonnell at the University of Pennsylvania School of Veterinary Medicine, Hal Schott at Michigan State University's Department of Large Animal Clinical Sciences, and Thomas Tobin at the University of Kentucky's Gluck Equine Research Center.

Like  Slate  and the Explainer  on Facebook. Follow us on Twitter.

David Sessions is a former Slate intern. He is currently a blogger at Politics Daily.

TODAY IN SLATE

The World

The Budget Disaster that Sabotaged the WHO’s Response to Ebola

Are the Attacks in Canada a Sign of ISIS on the Rise in the West?

PowerPoint Is the Worst, and Now It’s the Latest Way to Hack Into Your Computer

Is It Offensive When Kids Use Bad Words for Good Causes?

Fascinating Maps Based on Reddit, Craigslist, and OkCupid Data

Culturebox

The Real Secret of Serial

What reporter Sarah Koenig actually believes.

Culturebox

The Actual World

“Mount Thoreau” and the naming of things in the wilderness.

In Praise of 13th Grade: Why a Fifth Year of High School Is a Great Idea

Can Democratic Sen. Mary Landrieu Pull Off One More Louisiana Miracle?

  News & Politics
Politics
Oct. 23 2014 3:55 PM Panda Sluggers Democrats are in trouble. Time to bash China.
  Business
Business Insider
Oct. 23 2014 2:36 PM Take a Rare Peek Inside the Massive Data Centers That Power Google
  Life
Atlas Obscura
Oct. 23 2014 1:34 PM Leave Me Be Beneath a Tree: Trunyan Cemetery in Bali
  Double X
The XX Factor
Oct. 23 2014 11:33 AM Watch Little Princesses Curse for the Feminist Cause
  Slate Plus
Working
Oct. 23 2014 11:28 AM Slate’s Working Podcast: Episode 2 Transcript Read what David Plotz asked Dr. Meri Kolbrener about her workday.
  Arts
Brow Beat
Oct. 23 2014 4:03 PM You’re Doing It Wrong: Puttanesca Sauce
  Technology
Technology
Oct. 23 2014 4:36 PM Vampire Porn Mindgeek is a cautionary tale of consolidating production and distribution in a single, monopolistic owner.
  Health & Science
Bad Astronomy
Oct. 23 2014 7:30 AM Our Solar System and Galaxy … Seen by an Astronaut
  Sports
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.