Why do Only 3yr Old Horses Race in the Kentucky Derby?

Written by Beulah Martin
Mare and foal together in field

I have been asked before why only 3 year old thoroughbreds can race in the Kentucky Derby and honestly there is not really a clear answer. There are some speculations why this rule exists and I will share them with you here.

So why do only 3 year olds run in the Kentucky Derby? Likely it’s just tradition. In the past, racing in England had three races that compare to our Triple Crown and they limited the entrants to 3 year old competitors. When America began their organized thoroughbred racing they followed suit with the English tradition in some of their most competitive races.

Well that makes sense, but that still leaves a good question. Why did England and America think racing 3 year olds against 3 year olds was a good idea.

A matter of maturity

Most of our races like the Kentucky Derby, are Graded Stakes Races where there are fees assigned for an entry fee. This is where most of the runners purse money comes from.

These Stake Races are usually run with horses that are alike. The same class or ability, same gender or age of the horse.

The Kentucky Derby is a Grade 1 Stakes Race. Since a horse is usually fully mature around the age of 4 and a horse of 2 years old is not quite known for his ability, a 3 year old is the perfect age to see what they can do.

A 4 year old and older can usually run faster than a 3 year old. A 3 year old  horse will usually mature around 3 ½ to 4 years old, and so he is like the junior team compared to the senior team.

The competitive nature of the thoroughbred owners and trainers made them eager to see what their young prospects would do when matched against the colts or fillies in the other stud farms barn.

So the race of the year, The Kentucky Derby, was designed to watch the 3 year old compete against his peer group of other 3 year olds.

They added two other races to the event, the Preakness and the Belmont, and called it The Triple Crown.

The Spoils go to the winner

It is such a tremendous accomplishment to even get to run in the Kentucky Derby. The owners and trainers have been working toward getting their horse nominated and then qualified and finally entered into the race since the breeding of the mare to the stallion 4 years earlier. It’s the goal and dream of every horseman in the country.

It’s impossible to name all the awards and fame that this proven 3 year old will win if he wins the Kentucky Derby.

Then if he goes on to win the other two races and is crowned the winner of the Triple Crown he has just tripled his worth and desirability.

Even though he is only 3 years old, he is usually retired at the end of the racing season.

He will be retired and used for breeding, where his breeding fee will probably be the highest around.

Some owners have been known to make $80 million in a year just for breeding their champion horses.

Are race horses always male?

Mares, or fillies as they are called, are just as capable of being a great race horse as a male. However, they are not normally entered into the same races. There are always races scheduled on different tracks race cards that are just for the female horses. They can be entered into The Kentucky Derby by earning points the same way the males have to qualified. You can read all about this points process of how horses earn their way into the Kentucky Derby here on our article of the road to the Derby.

In fact, at Churchill Downs on the day before the Kentucky Derby there is a race for 3 year old fillies called The Kentucky Oaks. This is a 1 million Dollar Graded 1 race that the filly has to qualify for. They have even matched “the run for the roses” slogan with “the lilies for the fillies.”

One reason the owners don’t worry so much about campaigning their mares against the males is there is not as much money to be made when a mare wins the big races.

In fact only 3 fillies have ever won the Kentucky Derby and none have won the Triple Crown. When a mare is retired from racing, she usually becomes a broodmare. It is nature’s design that they can only have one foal a year. Whereas, a Stud can sire 150 to over 200 foals in one year.

Related Questions

Why do horses race for only one year? Horses can race from a 2 year old until the age of 10 or so, as long as they are sound. It seems like they might just race 1 year if you only follow the Kentucky Derby. A winner of that race does usually retire at the end of the year.

Was there a Triple Crown winner in 2018? The horse Justify, trained by Bob Baffert and ridden by Mike Smith won the Triple Crown in 2018. He was the 13th horse to ever win. American Pharaoh won the Triple Crown in 2015 after 37 years of no one being able to win it. These two horses are the only living winners of The Triple Crown.