Walk into any stable or spend a morning at the rail of a Triple Crown workout, and you’ll hear the same old arguments. People love to talk about "colt power." There is this long-standing assumption in the equestrian world that the boys just have another gear that the girls can't reach. But is it actually true? Are male horses faster than female horses, or have we just been looking at the data through a skewed lens for the last century?
It’s complicated. Honestly, if you just look at the raw speed figures from the Kentucky Derby or the Breeders’ Cup Classic, you might think the case is closed. Males win most of the "open" Grade 1 races. But that doesn’t tell the whole story. Genetics, hormones, and—perhaps most importantly—how we train and race these animals play massive roles in who crosses the wire first.
The Biological Reality of Horse Speed
Biology doesn't lie, but it also doesn't care about our assumptions. When we talk about male horses, we’re usually talking about "entire" males (stallions/colts) or geldings (castrated males). Females are fillies (under five) or mares.
Physiologically, colts tend to be larger. They often have more muscle mass, particularly in the hindquarters, which is the engine of the horse. This is largely thanks to testosterone. It’s the same reason male human sprinters generally have faster world records than female sprinters. A bigger engine usually means more raw horsepower.
However, horses aren't machines.
Female horses often have a higher "heart-to-weight" ratio. Some of the greatest runners in history, like the legendary Secretariat, had an abnormally large heart (a condition called the "X-factor" often passed down through the female line), but mares like Zenyatta and Rachel Alexandra proved that a female's cardiovascular system can be every bit as efficient as a male's. In fact, many trainers will tell you that fillies are often more "economical" in their stride. They might not have the raw, explosive bulk of a stallion, but they can be incredibly efficient over distance.
Why the Data is Kinda Messy
If you look at the history of the Kentucky Derby, only three fillies have ever won: Regret (1915), Genuine Risk (1980), and Winning Colors (1988). That looks like a slam dunk for the males.
But wait.
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We rarely run fillies against colts. In the racing world, most "classic" races are technically open to both sexes, but there is a massive parallel system of "fillies-only" races. Owners and trainers usually prefer to run their fast females against other females because it’s "safer" for their breeding value. If a filly loses to a colt, people might think she’s not elite. If she dominates other fillies, she stays a superstar.
This creates a massive selection bias. The best females are often kept away from the best males. When they do meet, it’s usually because the female is so freakishly fast that her owners have no choice but to let her run with the boys. And guess what? When they do, they often win.
Think about Enable. Or Black Caviar.
Black Caviar, the Australian sprinting queen, went 25-0. She didn't just beat females; she humiliated the best male sprinters in the world. She had a stride length that defied logic. When she moved, it looked like she was playing with them. In those moments, the "are male horses faster than female horses" debate feels pretty silly.
The Testosterone Factor and the Gelding Wildcard
Testosterone makes colts aggressive. That can be a good thing on the track—it gives them that "will to win" or the "grit" to push through a tight gap between horses. But it’s a double-edged sword. Stallions can be distracted. They get heavy in the neck. They lose focus because they’re thinking about, well, being stallions.
This is why we have geldings.
Geldings are often the most consistent racers. They have the skeletal frame of a male but none of the hormonal distractions. Some of the fastest speed ratings in history belong to geldings like Wise Dan, who won back-to-back Breeders’ Cup Mile titles.
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Mares, on the other hand, deal with estrus cycles. A filly might be the fastest thing on four legs in April, but if she’s "in heat" on race day in May, her performance might dip. It’s a variable that trainers of male horses simply don't have to manage. This isn't about "weakness"—it's about biological cycles that affect focus and comfort.
What Science Says About the Gap
A study published in The Veterinary Journal analyzed decades of racing data to see if the gap between male and female performance was closing. Interestingly, while male horses generally clock times about 1% to 1.5% faster than females at the elite level, that gap is much smaller than the gap found in human athletics (where men are often 10-12% faster).
Why is the gap so small in horses?
Selective breeding.
For 300 years, we have bred Thoroughbreds for one thing: speed. We don't just breed fast stallions; we breed them to the fastest mares. Because the "speed genes" are so concentrated in the population, the biological differences between the sexes have been compressed. A "slow" colt is still way slower than an "elite" filly.
The Weight Allowance: Evening the Odds
In most races where males and females compete together, the females are given a "weight allowance." They usually carry 3 to 5 pounds less than the males. This is the industry's way of acknowledging that, on average, a male horse might have a slight muscular advantage.
Does it work?
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Usually, yes. It levels the playing field just enough that a truly talented mare can look a stallion in the eye at the top of the stretch and out-kick him. We saw this perfectly in the 2009 Breeders’ Cup Classic. Zenyatta, carrying 123 pounds, hunted down the best males in the world (carrying 126 pounds) and blew past them. It remains one of the most iconic moments in sports history. She wasn't "fast for a girl." She was just the fastest horse on the planet that day. Period.
Quarter Horses vs. Thoroughbreds
It’s worth noting that this debate changes depending on the breed. In Quarter Horse racing, which is all about raw, explosive power over a short distance (usually 440 yards), the males tend to hold a slightly firmer grip on the records. The sheer muscle mass required to hit 55 mph in a matter of seconds favors the heavier-muscled colts.
In Endurance racing, however, the tables often turn. Over 50 or 100 miles, the smaller, lighter frame of a mare can be an advantage. They dissipate heat better. They often carry less "useless" bulk, making them incredibly efficient over long distances. In the endurance world, nobody asks if the boys are faster. They just try to keep up with the mares.
Misconceptions That Just Won't Die
- "Mares are too moody to be fast." Total nonsense. Some of the toughest, most consistent "war horses" in racing history have been mares.
- "Colts have bigger lungs." While lung capacity scales with size, the limiting factor in horse speed is usually oxygen uptake and the spleen’s ability to "dump" red blood cells into the system. Both sexes do this incredibly well.
- "The records prove males are faster." Records prove that more males are entered into the fastest races. If 90% of the entrants in a race are male, a male will probably win. It’s basic math, not necessarily biological destiny.
Actionable Insights for Horse Enthusiasts and Bettors
If you're looking at a race card or deciding which horse is "better," don't let the sex of the horse be your primary filter. Instead, look at these specific factors:
- Speed Figures (Beyer or Timeform): These are sex-neutral. A 105 Beyer is a 105 Beyer, whether it was earned by a filly or a colt. If a filly is posting higher numbers than the boys in the race, she is the faster horse.
- The "Shipping" Factor: Fillies are sometimes more sensitive to traveling and changing environments than geldings. Check if she has won away from her home track.
- Pedigree: Look for "speed" influencers. If a mare is sired by a known speed-ball like Into Mischief, she's likely to have more raw early speed than a plodding colt.
- The Weight Break: In "Allowance" or "Stakes" races, check the weight. A 5-pound difference over a mile and a quarter is roughly two to three lengths. That is a massive advantage for a high-quality female.
At the end of the day, a fast horse is a fast horse. While the "average" male might be slightly faster than the "average" female due to muscle mass and testosterone, the elite level of the sport proves that these differences are marginal. When the gates open, the dirt doesn't care if the hooves hitting it belong to a king or a queen.
Focus on the individual’s biomechanics and past performances. The stopwatch doesn't have a gender bias, and neither should your evaluation of a horse's talent.
To accurately assess speed, always compare times on the same track surface under similar weather conditions. Track variants can change by the hour. A filly running on a "fast" track at noon might look faster than a colt running on a "deep" or "tiring" track at 4:00 PM. Always adjust for the track surface speed before making a final judgment on who holds the upper hand.
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