Chapter 3: Colors in Horses
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Chapter 5: Anatomy in Horses
Pregnancy lasts for approximately 335–340 days (11 months) and usually results in one foal. Twins are very rare. Birth takes place quickly, consistent with the status of a horse as a prey animal, and more often at night than during the day. Foals are born with an ability to quickly escape from predators; normally a foal will stand up and nurse within the first hour after it is born, can trot and canter within hours, and most can gallop by the next day. A newborn foal's legs are almost as long (90%) as those of an adult horse.
Colts are carried on average about 4 days longer than fillies. Healthy foals grow quickly and can put on up to three pounds or over a kilo a day. A sound diet improves growth and leads to a healthier adult animal, although genetics also plays a part. In the first weeks of life the foal gets everything it needs from the mare's milk. Like a human infant, it receives nourishment and antibodies from the colostrum in milk that is produced within the first few hours or days following parturition. The mare needs additional water to help her produce milk for the foal and may benefit from supplementary nutrition.
Horses, particularly colts, may sometimes be physically capable of reproduction at about 18 months. In practice, individuals 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; the precise time of completion of development also depends on the horse's size, breed, gender, and the quality of care provided by its owner. 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, but are crucial to development.
A foal may start to eat solids from ten days of age, after eight to ten weeks it will need more nutrition than the mare's milk can supply; supplementary feeding is required by then. It is important when adding solid food to the foal's diet to not overfeed the foal or feed an improperly balanced diet. This can trigger one of several possible growth disorders that can cause lifelong soundness problems. On the other hand, insufficient nutrition to mare or foal can cause stunted growth and other health problems for the foal as it gets older.
It is typical for foals under human management to be weaned between four and six months of age, though under natural conditions, they may nurse for longer, occasionally until the following year when the mare foals again. A foal that has been weaned but is less than one year old is called a weanling.
Mare's milk is not a significant source of nutrients for the foal after about four months, though it does no harm to a healthy mare for a foal to nurse a month or two longer and may be of some psychological benefit to the foal. A mare that is both nursing and pregnant will have increased nutritional demands made upon her in the last months of pregnancy, and therefore most domesticated foals are weaned some time in the autumn in the Northern Hemisphere.
Weanlings are not capable of reproduction. Puberty occurs in most horses during their yearling year. Therefore, some young horses are capable of reproduction prior to full physical maturity, though it is not common. Two year olds sometimes are deliberately bred, though doing so, particularly with fillies, may put undesirable stress on their still-growing bodies. As a general rule, breeding young horses prior to the age of three is considered undesirable.
Depending on maturity, breed, and the tasks expected, young 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 entered into top-level competition until they are a minimum of four years old, because their bones and muscles are not solidly developed, nor is their advanced training complete. For endurance riding competition, horses are not deemed mature enough to compete until they are a full 60 calendar months (5 years) old.
