Horse
Article by jekky
Biology Main article Equine anatomy Parts of a horse Horse anatomy is described by a large number of specific terms as illustrated by the chart to the right Specific terms also describe various ages colors and breeds 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 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 Gelding a castrated male horse of any age In horse racing these definitions may differ For example in the British Isles Thoroughbred horse racing defines colt and fillies as less than five years old However for Australian Thoroughbred racing colts and fillies are less than four years old Size and measurement See also Hand length The height of horses is measured at the highest point of the withers where the neck meets the back This point was chosen as it is a stable point of the anatomy unlike the head or neck which move up and down The English speaking world measures the height of horses in hands abbreviated h or hh for hands high and inches One hand is equal to 101 6 millimetres 4 in The height is expressed as the number of full hands followed by a decimal point then the number of additional inches Thus a horse described as 15 2 h is 15 hands 60 inches 152 4 cm plus 2 inches 5 1 cm for a total of 62 inches 157 5 cm in height Size varies greatly among horse breeds as with this full sized horse and a miniature horse The size of horses varies by breed but also is influenced by nutrition Light riding horses usually range in height from 14 to 16 hands 56 to 64 inches 142 to 163 cm and can weigh from 380 to 550 kilograms 840 to 1 200 lb Larger riding horses usually start at about 15 2 hands 62 inches 157 cm and often are as tall as 17 hands 68 inches 173 cm weighing from 500 to 600 kilograms 1 100 to 1 300 lb Heavy or draft horses are usually at least 16 to 18 hands 64 to 72 inches 163 to 183 cm high and can weigh from about 700 to 1 000 kilograms 1 500 to 2 200 lb The largest horse in recorded history was probably a Shire horse named Mammoth who was born in 1848 He stood 21 2 hands high 86 5 in 220 cm and his peak weight was estimated at 1 500 kilograms 3 300 lb 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 27 pounds 12 kg Ponies Main article Pony The general rule for height between a horse and a pony at maturity is 14 2 hands 58 inches 147 cm An animal 14 2 h or over is usually considered to be a horse and one less than 14 2 h a pony However there are many exceptions to the general rule In Australia ponies measure under 14 hands 56 inches 142 cm The International Federation for Equestrian Sports which uses metric measurements defines the cutoff between horses and ponies at 148 centimetres 58 27 in just over 14 2 h without shoes and 149 centimetres 58 66 in just over 14 2 1 2 h with shoes Some breeds which typically produce individuals both under and over 14 2 h considered all animals of that breed to be horses regardless of their height 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 The distinction between a horse and pony is not simply a difference in height but 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 may 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 In fact small size by itself is sometimes not a factor at all While the Shetland pony stands on average 10 hands 40 inches 102 cm 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 Colors and markings Main articles Equine coat color Equine coat color genetics and Horse markings Bay left and chestnut sometimes called sorrel are two of the most common coat colors seen in almost all breeds 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 Horses of the same color may be distinguished from one another by white markings which along with various spotting patterns are inherited separately from coat color Many genes that create horse coat colors have been identified although research continues to further identify factors that result in specific traits One of the first genetic relationships to be understood was that between recessive red chestnut and dominant black which is controlled by the red factor or extension gene Additional alleles control spotting graying suppression or dilution of color and other effects that create the dozens of possible coat colors found in horses Common colors include black various shades of reddish brown such as chestnut and bay and gray citation needed Horses which are white in coat color are often mislabeled as white horses However a horse that looks white is usually a middle aged or older gray Grays are born a darker shade get lighter as they age and usually have black skin underneath their white hair coat with the exception of pink skin under white markings The only horses properly called white are born with a white hair coat and have predominantly pink skin a fairly rare occurrence There are no truly albino horses having both pink skin and red eyes Reproduction and development Main article Horse breeding Gestation lasts for approximately 335340 days and usually results in one foal Twins are rare Horses are a precocial species and foals are capable of standing and running within a short time following birth Horses particularly colts sometimes are physically capable of reproduction at about 18 months but domesticated horses are rarely allowed to breed before the age of three especially females Horses four years old are considered mature although the skeleton normally continues to develop until the age of six maturation also depends on the horse s size breed sex and quality of care Also if the horse is larger its bones are larger therefore not only do the bones take longer to actually form bone tissue but the epiphyseal plates are also larger and take longer to convert from cartilage to bone These plates convert after the other parts of the bones and are crucial to development Depending on maturity breed and work expected horses are usually put under saddle and trained to be ridden between the ages of two and four Although Thoroughbred race horses are put on the track at as young as two years old in some countries horses specifically bred for sports such as dressage are generally not put under saddle until they are four years old because their bones and muscles are not solidly developed For endurance riding competition horses are not deemed mature enough to compete until they are a full 60 calendar months 5 years old Anatomy Main article Equine anatomy See also Muscular system of the horse Respiratory system of the horse and Circulatory system of the horse Skeletal system Main article Skeletal system of the horse The skeletal system of a modern horse Horses have a skeleton that averages 205 bones A significant difference between the horse skeleton and that of a human is the lack of a collarbonehe horse s forelimbs are attached to the spinal column by a powerful set of muscles tendons and ligaments that attach the shoulder blade to the torso The horse s legs and hooves are also unique structures Their leg bones are proportioned differently from those of a human For example the body part that is called a horse s knee is actually made up of the carpal bones that correspond to the human wrist Similarly the hock contains bones equivalent to those in the human ankle and heel The lower leg bones of a horse correspond to the bones of the human hand or foot and the fetlock incorrectly called the ankle is actually the proximal sesamoid bones between the cannon bones a single equivalent to the human metacarpal or metatarsal bones and the proximal phalanges located where one finds the knuckles of a human A horse also has no muscles in its legs below the knees and hocks only skin hair bone tendons ligaments cartilage and the assorted specialized tissues that make up the hoof Hooves Main article Horse hoof See also Horseshoe and Farrier The critical importance of the feet and legs is summed up by the traditional adage no foot no horse The horse hoof begins with the distal phalanges the equivalent of the human fingertip or tip of the toe surrounded by cartilage and other specialized blood rich soft tissues such as the laminae The exterior hoof wall and horn of the sole is made of essentially the same material as a human fingernail The end result is that a horse weighing on average 500 kilograms 1 100 lb travels on the same bones as would a human on tiptoe For the protection of the hoof under certain conditions some horses have horseshoes placed on their feet by a professional farrier The hoof continually grows and needs to be trimmed and horseshoes reset if used every five to eight weeks Teeth Main article Horse teeth Horses are adapted to grazing In an adult horse there are 12 incisors adapted to biting off the grass or other vegetation at the front of the mouth There are 24 teeth adapted for chewing the premolars and molars at the back of the mouth Stallions and geldings have four additional teeth just behind the incisors a type of canine teeth that are called tushes Some horses both male and female will also develop one to four very small vestigial teeth in front of the molars known as wolf teeth which are generally removed because they can interfere with the bit There is an empty interdental space between the incisors and the molars where the bit rests directly on the bars gums of the horse s mouth when the horse is bridled The incisors show a distinct wear and growth pattern as the horse ages as well as change in the angle at which the chewing surfaces meet The teeth continue to erupt throughout life as they are worn down by grazing so a very rough estimate of a horse s age can be made by an examination of its teeth although diet and veterinary care can affect the rate of tooth wear Digestion Main articles Equine anatomy Digestive system and Equine nutrition Horses are herbivores with a digestive system adapted to a forage diet of grasses and other plant material consumed steadily throughout the day Therefore compared to humans they have a relatively small stomach but very long intestines to facilitate a steady flow of nutrients A 450 kilogram 990 lb horse will eat 7 to 11 kilograms 15 to 24 lb of food per day and under normal use drink 38 litres 8 4 imp gal 10 US gal to 45 litres 9 9 imp gal 12 US gal of water Horses are not ruminants so they have only one stomach like humans but unlike humans they can also digest cellulose from grasses due to the presence of a hind gut called the cecum or water gut which food goes through before reaching the large intestine Unlike humans horses cannot vomit so digestion problems can quickly cause colic a leading cause of death Senses See also Equine vision A horse s eye The horse s senses are generally superior to those of a human As prey animals they must be aware of their surroundings at all times They have the largest eyes of any land mammal and because their eyes are positioned on the sides of their heads horses have a range of vision of more than 350 with approximately
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