Domestic horse

The Horse, is a large land mammal notable for its speed, strength, and endurance. Horses are members of the Equidae family, which also includes zebras and asses. Like all equids, the horse is extremely well designed to traveling long distances with great efficiency and to surviving on a diet of nutrient-poor, high-fiber grasses. The horse is an intensely social animal, forming strong associations with members of its herd and possessing a keen ability to recognize subtle social cues. These instinctive behaviors form the basis of the horse’s ability to bond with and obey a human trainer.

The horse’s influence on human history and civilization make it one of the most important domestic animals. Horses were domesticated around 3,000 years ago. Throughout much of human history, they have provided humans with mobility and have served in agriculture, warfare, and sport. Today domestic horses are found throughout the world, with a total population estimated at 60 million. So-called wild horses, such as those found in the American West, are actually feral animals, free-living descendants of domestic horses that escaped or were turned loose.

The ancestors of modern horses, as well as zebras and asses, were created on the sixth day of creation. After the flood, the horse spread out to other parts of the world from the area of Babylonia in modern-day Iraq. Horses had crossed over the Bering Strait land bridge from Siberia into North America. Eventually, horses became extinct in the Americas. They were not seen in the Americas again until 1494, when Italian explorer Christopher Columbus transported them on ships from Spain on his second voyage to the New World.

Anatomy
As a result of deliberate breeding by humans, horses display a remarkable variation in size, body shape, and coat color. Traditionally, a horse’s size is measured at the withers—an elevated part of the spine between the neck and the back. The measurement is made in hands; one hand equals about 10 cm (4 in). Typical riding horses stand 14 to 16 hands high and weigh 400 to 500 kg (900 to 1,100 lb).

Coat
The horse has a hairy coat and a long mane and tail. A heavy winter coat grows in the fall and sheds in the spring. Typical coat colors include black, brown, gray, cream, gold, and white. The mane and tail can be the same or different from the body color, and many variations in color can result from inherited traits that cause spotting, dilution of the basic coat colors, or a sprinkling of white hairs in the coat. Many color patterns have specific names, such as bay (brown with black mane and tail), chestnut (reddish brown with mane and tail of the same or lighter color), and palomino (gold with a creamy white mane and tail).

Head
A horse’s head is composed of the cranium, which encloses the animal’s large, complex brain, and the face, distinguished by a long muzzle consisting of the nose and lips. The muzzle provides enough distance between the horse’s mouth and its eyes so that it can graze and watch for danger at the same time.

Horses have the largest eyes of any land mammal. The large eyes protrude from the sides of the head, enabling horses to see almost directly behind themselves, even while facing forward. Their night vision is excellent. Horses have limited color vision, which appears to be similar to one of the less common forms of color blindness in humans—they perceive red and blue, but they cannot distinguish between green and shades of gray.

Horses have powerful teeth and jaws to grind and break down plant fibers. Their teeth grow continuously as their surfaces wear down. Male horses usually have 40 teeth and females have 36. Between the front incisors and the rear molars is a gap called the diastema, where the bit is placed. Horses can close their wide nostrils against dusty winds, and they can move their large ears to detect sounds from various directions.

Body
A horse’s head is held up by its long, flexible neck, which lets the horse reach down to the ground to feed, rise to a high vantage point to sight danger, and bite itches on the front part of its body. The horse’s body has a wide chest, which holds its enormous lungs and heart; and a muscular back, beneath which lie the horse’s internal organs for digesting food and reproducing. A horse’s long, flowing tail helps keep its hindquarters warm and is used to swish away insects.

Legs
The specialized structures of the horse’s legs make the animal a very efficient runner. What we think of as the horse’s knee is actually the equivalent of a human’s ankle, so from the knee down the leg is really a highly elongated foot. The lowest part of the foot is the tip of a single toe, which corresponds to the tip of a person’s middle toe. This large, strong toe tip is well protected by a tough, curved hoof. By “standing on its toes,” the horse has a very long leg for an animal of its size, but also a very light leg, since toes are lightweight structures, carrying a minimum of bone and tendon and no muscle at all. Like a person’s foot, a horse’s foot has a sole. In the horse, the sole includes a rubbery, V-shaped structure called the frog, which helps absorb the impact of the foot against the ground.

Many of the joints in horses’ legs are comparable to hinges that permit forward and backward motion only. This type of joint requires fewer muscles than are needed for the kind of ball-and-socket joint that occurs in the human hip, which can rotate in any direction. This yields a further savings in weight. Long, light legs allow a horse to move very efficiently. A long leg produces a long stride, and a light leg allows the horse to swing its limbs back and forth quickly with a minimal expenditure of energy. The top speed of the horse is about 70 km/h (45 mph).

Anatomy terms
Poll - The point where the head meets the neck, just behind the ears.

Bridle Path - An area at the start of the mane, commonly shaved to accommodate bridal straps.

Crest - The top portion of the neck, generally more pronounced in studs.

Withers - The highest point of the back, just above the shoulder blades. Horse height is measured at the withers.

Loin - The area just behind where a saddle sits, the space from the last vertebrae to the croup.

Hip - The hip joint is the topmost portion of the rump.

Croup - Begins at the top of the hip and extends down to the dock where the tail begins.

Dock - The point where the rump and the tail connect.

Point of Buttock - The rounded edge of the rump.

Hock - The bending joint (corresponds to the knee on the front legs) on the hind leg.

Gaskin - The large muscle just above the hock on the inside of hind legs.

Stifle - The joint where the hind legs connect to the body.

Flank - Area where hind legs meet the barrel just past the stifle and just before the ribcage.

Barrel - Body of horse, essentially the area enclosed in the ribcage.

Elbow - The joint where the front leg meets the body of the horse.

Chestnut - A horny growth on the inside of each front leg.

Ergot - A horny growth on the back side of the fetlock joint.

Fetlock - The “ankle” joint (although really closer to the ball of the foot in anatomy) connecting the hoof to the leg.

Hoof - The foot, Hard on the outside and softer on the inside. The hoof is a harder version of our fingernails.

Coronet - Ring of soft tissue around the top of the hoof where it meets the skin.

Pastern - The space between the coronet band and the fetlock.

Cannon - The long, slender space between the knee and fetlock joints.

Knee - The bending joint of the front legs.

Forearm - The area between the knee and the elbow of the front legs

Heart Girth - Or girth, the area just behind the elbow, where the saddle girth sits. Should be the largest diameter of the horse’s barrel.

Point of Shoulder - The front most part of the horse’s chest.

Shoulder - The space between the withers and the point of shoulder

Throatlatch - Where the windpipe meets the jaw. Often where the strap of a bridle lays.

Jaw - The bottom circular portion of the horse's face.

Muzzle - Chin, mouth and nose are all parts of the muzzle.

Forelock - A section of the mane which grows at the top of the forehead.

Reproduction


All horses breed sexually and give birth to live young (viviparous). They are seasonal breeders; meaning there is only a specific season in which a horse will mate. Most mares give birth in the spring to a single baby (foal), sometimes twins. The mare carries her foal for 11 months, and produces milk for their young and will feed them for several months. When the foal is born it only takes 1 – 2 hours for it to be able to stand up and walk.

Horses reach sexual maturity at about one and a half years. The estrous cycle in the mare—a mature female horse—typically lasts 21 days. During the first five days of the cycle, the mare is usually receptive to mating. The estrous cycle stops during winter and resumes in the spring, which is the start of the breeding season. A stallion—a mature male horse—approaching a mare in estrus engages in various courtship rituals. These include uttering nickering sounds and sniffing and licking the mare’s genital area.

Among feral horses, stallions guard a harem of mares and compete with other stallions for “ownership” of mares. A harem commonly consists of a single stallion, one to three mares, and their immature offspring. Stallions challenge one another by competing in lengthy squealing contests; often a horse that squeals the longest is able to claim the superior position without physical combat. Stallions that take over a harem from another male will often cause abortions in pregnant mares by chasing and aggressively attacking them. This allows the new stallion to immediately rebreed the mares and produce his own offspring. To control aggressive behavior in stallions, which is closely linked to the hormone testosterone produced in the testes, horse owners usually castrate males that will not be used for breeding. A castrated male horse is called a gelding.

When trying to attract a mate, the female horse (mare) urinates by raising her tail and revealing her vulva. When a male horse (stallion) notices her he approaches with a high head and tail and his ears drooped backwards. He will nicker, nip, nudge her, and then sniff her urine to determine her sexual maturity (973 days; average). This behavior stimulates the mare's secretion and the stallion's erection. If both the mare and stallion are satisfied with each other, he will mount her and copulation will occur. Often they will periodically repeat courtship and breeding.

The gestational period in the horse averages 11 months. Mares generally give birth to a single offspring, or on rare occasions, twins. Young horses that have not yet been weaned are called foals. Young female horses are called fillies, and young males are called colts.

Giving birth normally takes place at night or in the early morning, and is usually over in 15 minutes. Once the foal is out, the mare will chew on the membranes/placenta to prevent the foal from suffocating and then lick the foal to help blood circulation. In fifteen minutes, the foal will attempt to stand and get milk from its mother. When foals are born their legs are almost the same length as they are when they are fully grown; their legs are so long they find it difficult to reach down to the grass to eat. Foals can focus with their eyes almost as soon as they are born. The foal is born without teeth, but they cut their first teeth within a week. As it gets older, the horse grows teeth. By the time the foal is six to nine months the young horse has all of its milk teeth. At five to six years of age, the horse replaces its milk teeth with permanent teeth. Horses are fully grown by 3 - 4 years of age.

Related References

 * MSN Encarta: Horses