A yearling is a young horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

 of either sex that is between one and two years old. Yearlings are comparable in development to a very early adolescent, they are not fully mature physically, and while they may be in the earliest stages of sexual maturity, they are considered too young to be breeding stock.

In addition, the word colt

Colt (horse)

A colt is a young male horse, under the age of four. The term "colt" is often confused with foal, which refers to a horse of either sex under one year of age....

 may also be used to describe a male horse, and the term filly

Filly

A filly is a young female horse too young to be called a mare. There are several specific definitions in use.*In most cases filly is a female horse under the age of four years old....

 is used to describe a female horse. Both "colt" and "filly" describe not only yearlings, but any other young horse under the age of four.

Development and training

Generally, the training

Horse training

Horse training refers to a variety of practices that teach horses to perform certain behaviors when asked to do so by humans. Horses are trained to be manageable by humans for everyday care as well as for equestrian activities from horse racing to therapeutic horseback riding for people with...

 of yearlings consists of basic gentling on the ground; most are too young to be ridden or driven. Yearlings are often full of energy and quite unpredictable. Even though they are not fully mature, they are heavier and stronger than a human and require knowledgeable handling. Many colts who are not going to be used as breeding stallions

Stallion (horse)

A stallion is a male horse that has not been gelded .Stallions will follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone may give stallions a thicker, "cresty" neck, as well as a somewhat more muscular physique as compared to...

 are gelded

Gelding

A gelding is a castrated horse or other equine such as a donkey or a mule. Castration, and the elimination of hormonally driven behavior associated with a stallion, allows a male horse to be calmer and better-behaved, making the animal quieter, gentler and potentially more suitable as an everyday...

 at this age—in part to improve their behavior.

Under ideal conditions, a yearling will have already been trained as a suckling or weanling foal

Foal

A foal is an equine, particularly a horse, that is one year old or younger. More specific terms are colt for a male foal and filly for a female foal, but these terms are used until the horse is age three or four. When the foal is nursing from its dam , it may also be called a suckling...

 to lead, to have its hooves

Horse hoof

A horse hoof is a structure surrounding the distal phalanx of the 3rd digit of each of the four limbs of Equus species, which is covered by complex soft tissue and keratinised structures...

 handled, to be groomed

Horse grooming

Horse grooming is hygienic care given to a horse, or a process by which the horse's physical appearance is enhanced for horse shows or other types of competition.-Reasons for grooming:...

, clipped, blanketed

Horse blanket

A horse blanket or rug is a blanket or animal coat intended for keeping a horse or other equine warm or otherwise protected from wind or other elements. They are tailored to fit around a horse's body from chest to rump, with straps crossing underneath the belly to secure the blanket yet allowing...

 and loaded into a horse trailer

Horse trailer

A horse trailer or horse van is used to transport horses...

. If these tasks have not been accomplished, the yearling year is a time they are often done, in part to get the horse used to human handling before it reaches its full adult strength.

Other than basic gentling, training and management of yearlings has many areas of dispute, mainly because some yearlings look very mature and strong, even though they do not yet have the skeletal

Skeletal system of the horse

The skeletal system of the horse has three major functions in the body. It protects vital organs, provides framework, and supports soft parts of the body. Horses typically have 205 bones...

 structure to support hard work. Yearlings grow at different rates and some horse breeds mature faster than others. For example, some people teach longeing

Longeing

Longeing or lungeing is a technique for training horses, where a horse is asked to work at the end of a long line and respond to commands from a handler on the ground who holds the line. It is also a critical component of the sport of equestrian vaulting...

 or roundpenning to yearlings, others avoid it, arguing that work in small circles stresses the joints of the young horse, which are still "soft," and not fully developed. Thoroughbred

Thoroughbred

The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...

 and American Quarter Horse

American Quarter Horse

The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...

 race horses are often "backed", or put under saddle, during the autumn of their yearling year, after the age of 18 months, though the riders are generally very light in weight and the young horses are not actually raced at this age. Likewise, some draft horse

Draft horse

A draft horse , draught horse or dray horse , less often called a work horse or heavy horse, is a large horse bred for hard, heavy tasks such as ploughing and farm labour...

 breeds and yearling Standardbreds are introduced to a harness

Horse harness

A horse harness is a type of horse tack that allows a horse or other equine to pull various horse-drawn vehicles such as a carriage, wagon or sleigh. Harnesses may also be used to hitch animals to other loads such as a plow or canal boat....

 and the concept of pulling an object, though they are not asked to handle any significant amount of weight. Conversely, breeds such as the Lipizzan

Lipizzan

The Lipizzan or Lipizzaner , is a breed of horse closely associated with the Spanish Riding School of Vienna, Austria, where the finest representatives demonstrate the haute école or "high school" movements of classical dressage, including the highly controlled, stylized jumps and other movements...

 do not even consider putting a young horse under saddle until it is four years old.

Some breeding farms tend to leave yearlings alone to grow in pastures and natural settings, others keep them stabled and condition them intensively for show or sale. For business purposes, the yearling year is considered a good time for breeders to sell young horses. One of the most famous horse auctions in the world is the Keeneland yearling sale

Keeneland Sales

The Keeneland Sales is an American Thoroughbred auction house in Lexington, Kentucky founded in 1935 as a nonprofit racing/auction entity on 147 acres of farmland west of Lexington, which had been owned by Jack O. Keene...

 in Kentucky

Kentucky

The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...

, where young Thoroughbred

Thoroughbred

The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...

 yearlings are put up for sale to the highest bidder, generally selling for prices in the five and six figures, but sometimes bringing prices in the millions.

The world of halter

Halter (horse show)

"Halter" is a term used to describe a type of horse show class where horses are shown "in hand," meaning that they are led, not ridden, and are judged on their conformation and suitability as breeding stock...

 exhibition is another area of controversy. Because larger, more mature yearlings place better in halter (or in-hand) classes at horse show

Horse show

A Horse show is a judged exhibition of horses and ponies. Many different horse breeds and equestrian disciplines hold competitions worldwide, from local to the international levels. Most horse shows run from one to three days, sometimes longer for major, all-breed events or national and...

s, and hence sell sooner and for better prices, there is a temptation to over-feed young horses and provide supplemental products, such as steroid

Steroid

A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...

s, to promote rapid growth. Such practices may have long-term health implications for the future athletic career of the young animal and may put it at risk for growth disorders.