Age

Depending on breed, management and environment, the domestic horse today has a life expectancy of 25 to 30 years. It is uncommon, but a few animals live into their 40s and, occasionally, beyond. The oldest verifiable record was "Old Billy", a 19th-century horse that lived to the age of 62. In modern times, Sugar Puff, who had been listed in the Guinness Book of World Records as the world's oldest living pony, died in 2007, aged 56.

Regardless of a horse's actual birth date, for most competition purposes an animal is considered a year older on January 1 of each year in the northern hemisphere and August 1 in the southern hemisphere. The exception is in endurance riding, where the minimum age to compete is based on the animal's calendar age.A very rough estimate of a horse's age can be made from looking at its teeth.

The following terminology is used to describe horses of various ages:

* Foal: a horse of either sex less than one year old. A nursing foal is sometimes called a suckling and a foal that has been weaned is called a weanling.Most domesticated foals are weaned at 5 to 7 months of age, although foals can be weaned at 4 months with no adverse effects.
* Yearling: a horse of either sex that is between one and two years old.
* Colt: a male horse under the age of four. A common terminology error is to call any young horse a "colt", when the term actually only refers to young male horses.[citation needed]
* Filly: a female horse under the age of four.
* Mare: a female horse four years old and older.
* Stallion: a non-castrated male horse four years old and older. Some people, particularly in the UK, refer to a stallion as a "horse".
* A ridgling or "rig" is a male horse which has an undescended testicle or is improperly castrated. If both testicles are not descended, the horse may appear to be a gelding, but will still behave like a stallion.
* Gelding: a castrated male horse of any age, though for convenience sake, many people also refer to a young gelding under the age of four as a "colt".

In horse racing, the definitions of colt, filly, mare, and stallion may differ from those given above. In the UK, Thoroughbred horse racing defines a colt as a male less than five years old, and a filly as a female less than five years old. In the USA, both Thoroughbred racing and harness racing defines colts and fillies as four years old and younger.

Size

The English-speaking world measures the height of horses in hands, abbreviated "h" or "hh", for "hands high", measured at the highest point of an animal's withers, where the neck meets the back, chosen as a stable point of the anatomy, unlike the head or neck, which move up and down; one hand is 4 inches (10 cm). Intermediate heights are defined by hands and inches, rounding to the lower measurement in hands, followed by a decimal point and the number of additional inches between 1 and 3. Thus a horse described as "15.2 h", is 15 hands, 2 inches (62 in/160 cm) in height.[22] The size of horses varies by breed, but can also be influenced by nutrition.

The general rule for cutoff in height between what is considered a horse and a pony at maturity is 14.2 hands (58 in/150 cm). An animal 14.2 h or over is usually considered to be a horse and one less than 14.2 h a pony.[23] However, there are exceptions to the general rule. Some breeds which typically produce individuals both under and over 14.2 h are considered horses regardless of their height.[24] Conversely, some pony breeds may have features in common with horses, and individual animals may occasionally mature at over 14.2 h, but are still considered to be ponies.[25]

The distinction between a horse and pony is not simply a difference in height, but takes account of other aspects of phenotype or appearance, such as conformation and temperament. Ponies often exhibit thicker manes, tails and overall coat. They also have proportionally shorter legs, wider barrels, heavier bone, shorter and thicker necks, and short heads with broad foreheads. They often have calmer temperaments than horses and also a high level of equine intelligence that may or may not be used to cooperate with human handlers.[23] In fact, small size, by itself, is sometimes not a factor at all. While the Shetland pony stands on average 10 hands high (40 in/100 cm),[26] the Falabella and other miniature horses, which can be no taller than 30 inches (76 cm), the size of a medium-sized dog, are classified by their respective registries as very small horses rather than as ponies.[27]

Light riding horses such as Arabians, Morgans, or Quarter Horses usually range in height from 14 to 16 hands (56 to 64 in/140 to 160 cm) and can weigh from 850 to 1,200 pounds (390 to 540 kg). Larger riding horses such as Thoroughbreds, American Saddlebreds or Warmbloods usually start at about 15.2 hands (62 in/160 cm) and often are as tall as 17 hands (68 in/170 cm), weighing from 1,100 to 1,500 pounds (500 to 680 kg). Heavy or draft horses such as the Clydesdale, Belgian, Percheron, and Shire are usually at least 16 to 18 hands (64 to 72 in/160 to 180 cm) high and can weigh from about 1,500 to 2,000 pounds (680 to 910 kg).

The largest horse in recorded history was probably a Shire horse named Sampson, who lived during the late 1800s. He stood 21.2½ hands high (86.5 in/220 cm), and his peak weight was estimated at 3,360 pounds (1,520 kg).[28] The current record holder for the world's smallest horse is Thumbelina, a fully mature miniature horse affected by dwarfism. She is 17 inches (43 cm) tall and weighs 60 pounds (27 kg).[29]

Colors and markings

Horses exhibit a diverse array of coat colors and distinctive markings, described with a specialized vocabulary. Often, a horse is classified first by its coat color, before breed or sex. Flashy or unusual colors are sometimes very popular, as are horses with particularly attractive markings. Horses of the same color may be distinguished from one another by their markings.

The genetics that create many horse coat colors have been identified, although research continues on specific genes and mutations that result in specific color traits. Essentially, all horse colors begin with a genetic base of "red" (chestnut) or "black", with the addition of alleles for spotting, graying, suppression or dilution of color, or other effects acting upon the base colors to create the dozens of possible coat colors found in horses.

Horses which are light in color are often misnamed as being "white" horses. A horse that looks pure white is, in most cases, actually a middle-aged or older gray. Grays have black skin underneath their white hair coat (with the exception of small amounts of pink skin under white markings). The only horses properly called white are those with pink skin under a white hair coat, a fairly rare occurrence. There are no truly albino horses, with pink skin and red eyes, as albinism is a lethal condition in horses.