About Horses:
Horse is a common name for hoofed, herbivorous mammals that include the domestic
horse and three groups of undomesticated species. One group comprises the zebra, native to Africa; another consists of the ass, including
the kiang and onager of Asia and the wild ass of Africa. The third group contains
Przewalski’s wild horse, which is now found only in captivity. The only extant true
wild horse, it produces fertile offspring when crossed with the domestic horse. Other
so-called wild horses in various parts of the world, such as the mustang in
North America, are descendants of domestic horses that have reverted to a wild state.
Prehistoric Horses:
The evolution of the horse can
be traced through fossil remains to the Hyracotherium, originally identified as the
Eohippus: a small, leaf-browsing mammal of the Eocene Epoch, 55
million to 38 million years ago. Hyracotherium, about the size of a fox, had four
toes on its forefeet and three on its hind feet. Several species and related genera
appeared in North America and Eurasia during the Eocene. Then, apparently, the Eurasian
species died out, but the American species gave rise in the Oligocene Epoch, 38 million to
24 million years ago, to the genus Mesohippus.
In the Miocene Epoch, 24 million to 5 million years ago, Mesohippus
was succeeded by Hypohippus and Anchitherium. Both of these genera probably
migrated to Eurasia from North America. Other descendants of Mesohippus were Miohippus
and Merychippus; the latter genus developed high-crowned teeth, permitting it to
feed by grazing on grass rather than browsing on leaves. Among the descendants of Merychippus
in the Pliocene Epoch were Hipparion, which apparently spread from North America to
Eurasia, and Pliohippus, which appears to be the progenitor of the modern genus Equus,
which includes the domestic horse.
During the Pleistocene Epoch, which began 1.6 million years ago, the genus
Equus apparently spread from North America to Eurasia, Africa, and South America.
Subsequently, the native American horses died out, possibly as a result of disease. Cave
dwellings in Europe indicate that horses were plentiful on that continent during the early
Stone Age (about 2 million years ago to about 4000 BC). Dismembered skeletons of horses
have been found in sufficient numbers in and near Stone Age dwellings to show that horses
were frequently killed and eaten. In Neolithic times (about 4000 BC to 2000 BC), when
Europe was largely forested, the number of horses evidently declined. Remains of the
Bronze Age (about 1000 BC) include bits and pieces of harness, which clearly
demonstrate that horses had become domestic animals in this period.
Modern Horses:
The most marked anatomical characteristic of the modern horse is the
possession of a single toe on each of its four feet, which makes it a perissodactyl, or odd-toed ungulate, along with the rhinoceros and tapir. The horse’s toe, which corresponds to the middle digit of the human
hand, is much enlarged and protected by a horny hoof that surrounds the front and sides of
the toe. Vestigial splints corresponding to the second and fourth toes are situated on
either side of the foot above the hoof.
The skull of the horse is long; the facial bones are twice the length of
the cranium. The mandible, or lower jaw, is long and has a broad, flat plate at its lower
hind end. The spine is composed of 7 cervical, 18 dorsal, 6 lumbar, 5 sacral, and 15
caudal vertebrae. Horses have 44 teeth: 3 incisors, 1 canine, 4 premolars, and 3 molars on
each side of each jaw. The incisors, which are used for cropping grass and other herbage,
grow in the form of a semicircle. A pronounced gap exists between the canine teeth and the
premolars; the metal bit used for controlling a horse is placed in this gap when the
animal is ridden or driven. All the teeth have long crowns and comparatively short roots.
The horse has a simple stomach, and fermentation of fibrous food takes place in a blind
pocket, or cecum, analogous to the appendix in humans. It is located at the juncture of
the small and large intestines. In a large horse the cecum may have a capacity of about 38
liters (about 10 gallons).
Both male and female horses are sexually mature by the age of two. They
are seldom used for breeding purposes, however, before they are three years old. The
gestation period is about 11 months, and single births are the rule. Twins are a genuine
rarity, and only a few births of three or more foals have ever been recorded.
Gaits:
Horses are capable of a wide range of gaits; a few of them are
artificially developed by trainers. For simplicity they may be divided into symmetrical
gaits, in which equal time intervals separate the touching of the ground by the left
and right front legs (and also by the left and right hind legs); and asymmetrical
gaits, in which the time intervals are not equal. Familiar symmetrical gaits, in order
of increasing speed, include the walk, pace, and trot. A horse walks by swinging its legs
in the order of left front, right rear, right front, and left rear. It paces by swinging
the left and then the right legs nearly in unison, and trots by swinging the diagonally
opposite legs nearly in unison. Artificial symmetrical gaits include the slow gait, or
stepping pace, and the faster rack, or single-foot, both of which are done with legs
lifted high and no more than two legs on the ground at the same time. Asymmetrical gaits
include the canter and the faster gallop, in which the left and then the right hind leg
touches the ground, followed by the left and then the right front leg; the sequence may be
reversed right to left.
Kinds and Breeds:
Domestic horses were
introduced into Babylonia in about 2000 BC and into Egypt about 300 years later. The
animals were brought into Egypt by the Hyksos from northeastern Syria. These Egyptian and
Babylonian horses were the forerunners of the swift Arabian and related
desert breeds of the Middle East and northern Africa. Another strain of horses was
domesticated in Europe. Heavily built and slower but more powerful than the desert breeds,
they are regarded as the early ancestors of the modern draft horses used for plowing,
pulling wagons, and other heavy work. Some authorities also believe that a third ancestral
strain found in the British Isles was the prototype of various breeds of modern ponies.
Throughout most of Europe, from the early centuries AD to about the 17th
century, the powerful native horses were used for military mounts, for hauling heavy
loads, and as pack animals. During the same period the Arab world had developed smaller,
fast-galloping breeds, which were introduced into Spain after the Muslim conquest in the
8th century. The horses bred in Spain became famous for their speed and endurance and many
were imported into England and Europe as early as the 12th century. Systematic attempts to
improve extant breeds of horses, however, did not take place until the end of the 17th
century, when Arabian stallions were imported to England and France to breed with mares of
native stock.
The first domestic horses introduced into the Americas were of the Arabian
type, brought by the Spanish conquistadores and explorers in the 16th century. They are
believed to have lost or abandoned some of their horses, and these animals may have been
the source of herds of wild horses found in various parts of western North America. Horses
left by the Spanish also ran wild on the pampas of South America around the Río de la
Plata. The English settlers, especially the early Virginia colonists, also imported
horses.
In the last 300 years horse breeders have made continuous attempts to
improve the various breeds of horses and to develop strains that are particularly suited
for specialized tasks. The resultant new breeds include saddle horses and harness horses
especially adapted for racing gaits, hunters adapted for endurance, carriage horses and
draft horses for pulling heavy loads, and cattle horses, ponies, and polo ponies (small,
fast animals that can be trained to the complicated maneuvers of roping or the game of
polo).
The Arabian breed is often divided into three subbreeds: Turks from
European Turkey and Asia Minor, Arabians from the regions between Damascus and the
Euphrates River, and Barbs from the Barbary states of northern Africa.
Arabians in general are comparatively small horses, standing between 147 and 152 cm (58
and 60 in) at the withers (the high part of the back, located between the shoulder
blades), or 15 hands high. The height of a horse is frequently given in hands, one
hand—the width of a human hand—is equal to 10 cm (4 in). Arabians have
remarkable powers of endurance and are swift gallopers. All the saddle breeds are derived,
in large part, from Arabian stock.
The Thoroughbred was developed in the early 18th century from offspring of
three foundation sires—the Byerly Turk, the Darley Arabian, and the Godolphin
Barb—and native English mares. It is primarily used for flat-track racing, hunting,
and jumping. The American standardbred, developed in the northeastern United States in
colonial times, is a light harness type and is most often used in trotting or pacing
races. Biologically speaking, saddle horses are more properly types than breeds. Because
of the popularity of various equestrian sports and activities, registry and breed
associations have been established for such important show and racing horses as the
American saddle horse, the Tennessee
walker, the Morgan, and
the quarter horse. Saddle horses weigh much less than draft horses.
The breeds of draft horses are more distinct than those of saddle horses.
They include the Belgian heavy draft
horse, the English shire, the Clydesdale, and the Percheron. The Belgian is one of the largest of horses,
reaching a shoulder height of 173 cm (68 in) or more and weights of as much as 1125 kg
(2500 lb). The English shire is about the same size, but has long hair on the back of its
hind legs from its hooves up to the hock (a joint corresponding to the human ankle, but
bending backwards). These breeds represent refinements of the original horses of their
countries of origin. The Clydesdale, smaller than the above breeds, was developed in
Scotland by crossing native horses with Belgian heavy draft horses and the English shire.
The Percheron, which stands about 168 cm (66 in) at the shoulder, is a native of the
former district of Le Perche in northwestern France and was produced by crossing Arabian
horses with the old Flemish breed of which the Belgian heavy draft horse is the modern
representative.
Ponies are identified as those breeds which stand less than 152 cm (60 in)
or 15 hands high. The real differences between ponies and larger horses, however, are size
and action. The body of a pony is deeper in relation to its height than that of a horse,
and a pony usually is more sure-footed than a horse. Many ponies are native to Great
Britain: the Dartmoor, the Exmoor, and the Welsh mountain pony for instance. The smallest of the ponies is the Shetland, which
is only about 106 cm (about 42 in) high at the withers.
Scientific classification:
Horses belong to the family
Equidae of the order Perissodactyla. The domestic horse is classified as Equus
caballus. Przewalski’s wild horse is classified as Equus caballus przewalskii. |
