The English-speaking world measures the height of horses in hands, abbreviated "h" or "hh"; one hand is equivalent to 4 inches. Horses are measured at the highest point of an animal's withers (at the base of the neck). A horse described as 15.2 hh tall is 15 hands, 2 inches (62 inches).
A horse can rest and even doze while standing by locking one of its hind legs at the stifle joint (basically, the knee). A group of ligaments and tendons called the stay apparatus holds the leg in place with minimal muscle involvement. Horses will switch from leg to leg to prevent fatigue in the locked leg.
A female horse is called a mare and a male horse is called a stallion. In the wild, the mare decides when the herd moves on and usually only one stallion will stay with a herd.
Horses live in well-structured groups with clear followers and leaders. Without any human training, horses will line up behind a lead mare according to their rank in the herd, usually with a stallion guarding the rear.
A person who makes horse shoes and fits them onto the horses is called a farrier. Farriers also clip hooves, which grow like fingernails, to keep them from getting overgrown, as well as caring for hooves more generally.
The famous mustangs of the American West, like many other "wild" populations, are actually considered feral, descended from escaped domesticated horses. The only truly wild horses live in Mongolia: the Przewalski.
The Przewalski horse of Mongolia was declared extinct in the wild in the late 1960s. Thanks to an existing captive breeding program, a group was reintroduced to the wild in 1992, and has now successfully reproduced.
The Origin of Horses
The horse evolved 55 million years ago. A close, early relative of the horse is Hyracotherium, also known as an eohippus. The size of a large fox, Hyracotherium stood 10 inches high at its shoulders and had four toes on its front feet and three on its back.
The only surviving branch of the horse family is the genus Equus, which includes zebras, asses, and donkeys along with the horse.
Rhinoceroses and tapirs are the horse's closest living relatives outside the horse family.
As horses adapted to eating tough grasses, their teeth became tougher too. Longer teeth evolved that could wear down without wearing out.
The first domesticated horses were probably kept primarily as a source of food, rather than for work or for riding.
During the Han dynasty, the Chinese mounted an expedition to Fergana, in present-day Uzbekistan, to acquire superior horses. Fergana horses were famous for sweating blood--a mystery now thought to be caused by parasites under their skin.
Kazakh horse herders milk mares and ferment the milk to make koumiss, a mildly alcoholic drink thought to have healthful properties.
Horses At Work
In 1532, 168 Spanish soldiers, 62 on horseback, faced off against 80,000 Inca on foot in western South America and captured the emperor, Atahuallpa.
To protect against the poison gases used in World War I, both soldiers and horses wore gas masks. Horses' noses were covered but their eyes were not, since they could tolerate the poisons better than humans.
Though cavalry charges are now a thing of the past, there are still places where a horse is more useful than a truck. In 2002, for example, during the war in Afghanistan, some U.S. Special Forces rode horses in areas where the rugged terrain and lack of fuel made auto transport impractical.
In 1900, around 130,000 horses worked in Manhattan--more than ten times the number of yellow cabs on the streets of New York City today. A typical city horse produced up to 45 pounds (20 kilograms) of manure and 2 gallons (7.5 liters) of urine a day.
In April 1860, a new postal service called the Pony Express was launched. With railroads handling the eastern leg and horsemen racing day and night across the west, from Missouri to California, the Pony Express could get a letter from coast to coast in just 10 days for just five dollars, later reduced to one dollar. Prior to this, the fastest way to get a letter cross-country was still by horse-drawn stagecoach, which took 25 days or more.