Colors and markings

Colors and markings

Bay (left) and chestnut (sometimes called "sorrel") are two of the most common coat colors, seen in almost all breeds.

Main articles: Equine coat color, Equine coat color genetics, and Horse 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.^[33] Horses of the same color may be distinguished from one another by white markings,^[34] which, along with various spotting patterns, are inherited separately from coat color.^[35]
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.^[36]
Chestnut, bay, and black are the basic equine coat colors. These colors are modified by at least ten other genes to create all other colors, including dilutions such as palomino and spotting patterns such as pinto.^[36] 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.^[37] There are no truly "albino" horses having both pink skin and red eyes.^[38]

Reproduction and development

Main article: Horse breeding

Gestation lasts for approximately 335–340 days^[39] and usually results in one foal. Twins are rare.^[40] Horses are a precocial species, and foals are capable of standing and running within a short time following birth.^[41]
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.^[39] 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.^[42]
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.^[43] Although Thoroughbred race horses are put on the track at as young as two years old in some countries,^[44] horses specifically bred for sports such as dressage are generally not put under saddle until they are three or four years old, because their bones and muscles are not solidly developed.^[45] For endurance riding competition, horses are not deemed mature enough to compete until they are a full 60 calendar months (5 years) old.^[9]