Horse breeding is reproduction in horses, and particularly the human-directed process of selective breeding of animals, particularly purebred horses of a given breed. Planned matings can be used to produce specifically desired characteristics in domesticated horses. Furthermore, modern breeding management and technologies can increase the rate of conception, a healthy pregnancy, and successful foaling.
Terminology The male parent of a horse, a stallion, is commonly known as its sire and the female parent, the mare, is called its dam. A "foal" is a newly born or very young horse of either sex, a "colt" is a young male horse, and a "filly" is a young female. Though many horse owners might breed their mare to a local stallion in order to produce a companion animal, most professional breeders use selective breeding to produce horses of a given type or breed.
Usually a horse is considered "bred" where it is born, not where a mating takes place, though some breeds denote the country or state where conception took place as the origin of the foal.Montgomery, E.S, "The Thoroughbred", Arco, New York, 1973 AJC & VRC, "Australian Stud Book", Vol. 31, Ramsay Ware Stockland Pty. Ltd., North Melbourne, 1980 The "breeder", is the person who owned or leased the mare at the time of foaling. That individual may not have had anything to do with the mating of the mare.Stratton, Charles, The International Horseman's Dictionary, Lansdowne Press, Melbourne, 1978,
The term "half-brother" or "half-sister" usually only describes horses which have the same dam, but different sires,Summerhayes, RS, Encyclopaedia for Horsemen, Warne & Co, London & New York, 1966 while horses with the same sire but different dams are said to be "by the same sire", with no sibling relationship is implied.de Bourg, Ross, "The Australian and New Zealand Thoroughbred", Nelson, West Melbourne, 1980, "Full" (or "own") siblings have both the same dam and the same sire. The terms paternal half-sibling, and maternal half-sibling are also often used. Three-quarter siblings are horses out of the same dam, and are by sires that are either half-brothers (i.e. same dam) or who are by the same sire.Napier, Miles, "Blood Will Tell", JA Allen & Co, London, 1977
Thoroughbreds and Arabians are also classified through the "distaff" or direct female line, known as their "family" or "" line, tracing back to their foundation bloodstock or the beginning of their respective stud books. The female line of descent always appears at the bottom of a tabulated pedigree and is therefore often known as the bottom line. In addition, the maternal grandfather of a horse has a special term: .
"Linebreeding" technically is the duplication of fourth-generation or more distant ancestors. However, the term is often used more loosely, describing horses with duplication of ancestors closer than the fourth generation. It also is sometimes used as a euphemism for inbreeding, a practice that is generally frowned upon by horse breeders, though used by some in an attempt to change certain traits.
Estrous cycle of the mare
Effects on the reproductive system during the estrous cycle Changes in hormone levels can have great effects on the physical characteristics of the reproductive organs of the mare, thereby preparing, or preventing, her from conceiving. Uterus: increased levels of estrogen during estrus cause edema within the uterus, making it feel heavier, and the uterus loses its tone. This edema decreases following ovulation, and the muscular tone increases. High levels of progesterone do not cause edema within the uterus. The uterus becomes flaccid during anestrus. Cervix: the cervix starts to relax right before estrus occurs, with maximal relaxation around the time of ovulation. The secretions of the cervix increase. High progesterone levels (during diestrus) cause the cervix to close and become toned. Vagina: the portion of the vagina near the cervix becomes engorged with blood right before estrus. The vagina becomes relaxed and secretions increase. Vulva: relaxes right before estrus begins. Becomes dry, and closes more tightly, during diestrus.
Hormones involved in the estrous cycle, during foaling, and after birth The cycle is controlled by several hormones which regulate the estrous cycle, the mare's behavior, and the reproductive system of the mare. The cycle begins when the increased day length causes the pineal gland to reduce the levels of melatonin, thereby allowing the hypothalamus to secrete GnRH. GnRH (Gonadotropin releasing hormone): secreted by the hypothalamus, causes the pituitary to release two gonadotrophins: LH and FSH. LH (Luteinizing hormone): levels are highest 2 days following ovulation, then slowly decrease over 4–5 days, dipping to their lowest levels 5–16 days after ovulation. Stimulates maturation of the follicle, which then in turn secretes estrogen. Unlike most mammals, the mare does not have an increase of LH right before ovulation. FSH (Follicle-stimulating hormone): secreted by the pituitary, causes the ovarian follicle to develop. Levels of FSH rise slightly at the end of estrus, but have their highest peak about 10 days before the next ovulation. FSH is inhibited by inhibin (see below), at the same time LH and estrogen levels rise, which prevents immature follicles from continuing their growth. Mares may however have multiple FSH waves during a single estrous cycle, and diestrus follicles resulting from a diestrus FSH wave are not uncommon, particularly in the height of the natural breeding season. Estrogen: secreted by the developing follicle, it causes the pituitary gland to secrete more LH (therefore, these 2 hormones are in a positive feedback loop). Additionally, it causes behavioral changes in the mare, making her more receptive toward the stallion, and causes physical changes in the cervix, uterus, and vagina to prepare the mare for conception (see above). Estrogen peaks 1–2 days before ovulation, and decreases within 2 days following ovulation. Inhibin: secreted by the developed follicle right before ovulation, "turns off" FSH, which is no longer needed now that the follicle is larger. Progesterone: prevents conception and decreases sexual receptibility of the mare to the stallion. Progesterone is therefore lowest during the estrus phase, and increases during diestrus. It decreases 12–15 days after ovulation, when the corpus luteum begins to decrease in size. Prostaglandin: secreted by the endrometrium 13–15 days following ovulation, causes luteolysis and prevents the corpus luteum from secreting progesterone eCG – equine chorionic gonadotropin – also called PMSG (pregnant mare serum gonadotropin): chorionic gonadotropins secreted if the mare conceives. First secreted by the endometrial cups around the 36th day of gestation, peaking around day 60, and decreasing after about 120 days of gestation. Also help to stimulate the growth of the fetal gonads. Prolactin: stimulates lactation Oxytocin: stimulates the uterus to contract
Breeding and gestation
Horses in the wild mate and foal in mid to late spring. For domestic horses bred for competitive purposes, especially horse racing, it is desirable that they be born as close as possible to January 1 in the northern hemisphere and August 1 in the southern hemisphere,The Australian Racing Board uses August 1 as its standard cutoff date, but also uses the date of conception to determine age. A foal born on or after July 1 of a given calendar year is included in the birth cohort of that calendar year if his or her dam was covered no later than August 31 of the previous calendar year. See so as to be at an advantage in size and maturity when competing against other horses in the same age group. When an early foal is desired, stud farm managers will put the mare "under lights" by keeping on the barn lights in the winter to simulate a longer day, thus bringing the mare into estrus sooner than she would in nature. Mares signal estrus and ovulation by urination in the presence of a stallion, raising the tail and revealing the vulva. A stallion, approaching with a high head, will usually nicker, nip and nudge the mare, as well as sniff her urine to determine her readiness for mating. During copulation, the stallion usually ejaculates after 6 to 8 pelvic thrusts.
Once fertilized, the oocyte (egg) remains in the oviduct for approximately 5.5 more days, and then descends into the uterus. The initial single cell combination is already dividing and by the time of entry into the uterus, the egg might have already reached the blastocyst stage.
The gestation period lasts for about eleven months, or about 340 days (normal average range 320–370 days). During the early days of pregnancy, the conceptus is mobile, moving about in the uterus until about day 16 when "fixation" occurs. Shortly after fixation, the embryo proper (so called up to about 35 days) will become visible on trans-rectal ultrasound (about day 21) and a heartbeat should be visible by about day 23. After the formation of the endometrial cups and early placentation is initiated (35–40 days of gestation) the terminology changes, and the embryo is referred to as a fetus. True implantation – invasion into the endometrium of any sort – does not occur until about day 35 of pregnancy with the formation of the endometrial cups, and true placentation (formation of the placenta) is not initiated until about day 40-45 and not completed until about 140 days of pregnancy. The fetus's sex can be determined by day 70 of the gestation using ultrasound. Halfway through gestation the fetus is the size of between a rabbit and a beagle. The most dramatic fetal development occurs in the last 3 months of pregnancy when 60% of fetal growth occurs.
Colts are carried on average about 4 days longer than fillies.
Care of the pregnant mare Domestic mares receive specific care and nutrition to ensure that they and their foals are healthy. Mares are given vaccinations against diseases such as the Rhinopneumonitis (EHV-1) virus (which can cause miscarriage) as well as vaccines for other conditions that may occur in a given region of the world. Pre-foaling vaccines are recommended 4–6 weeks prior to foaling to maximize the immunoglobulin content of the colostrum in the first milk. Mares are dewormed a few weeks prior to foaling, as the mare is the primary source of parasites for the foal."Expectant Mare: Assuring the Health and Well-Being of the Pregnant Mare"
Mares can be used for riding or driving during most of their pregnancy. Exercise is healthy, though should be moderated when a mare is heavily in foal. Exercise in excessively high temperatures has been suggested as being detrimental to pregnancy maintenance during the embryonic period;Mortensen C, Choi YH, Hinrichs K, Ing N, Kraemer D, Vogelsang S, Vogelsang M. 2006. Effects of exercise on embryo recovery rates and embryo quality in the horse. Animal Repro. Sci. 94:395-397 however ambient temperatures encountered during the research were in the region of 100 degrees F and the same results may not be encountered in regions with lower ambient temperatures.