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Horse Breeding

Horse Breeding. Paul R Earl Facultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL 66451, Mexico. Light duration controls the annual sexual cycle.

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Horse Breeding

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  1. Horse Breeding Paul R EarlFacultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL 66451, Mexico

  2. Light duration controls the annual sexual cycle In most herbivores the male is responsible for the protection of the herd against predators. Also, the stallion will fend off competing males, and mares in heat (estrus) will fend off other mares from a stallion. Spring is favorable for births. Let’s pick April for birth. Then if gestation is about 3 months as in sheep, breeding took place in say December. If gestation is 11 months as in horses, breeding took place in April or even in June. Then we have short and long day animals. Goats breed in winter to have kids in spring, just as horses breed in spring to have foals in spring. Also, summer in one hemisphere is winter in the other.

  3. After the equinox which is 21 September, as days get shorter goats are turned on sexually and horses off. Horses begin to react on 21 December as the days begin to get longerand so do many other animals.Do chickens lay more eggs with more hours of light ? Which hormones are involved with ovulation ? These climatologic effects can lead to considerations of the biological clock.

  4. Detecting heat (estrus) by using a mare’s responsiveness to a stallion is known as teasing. It is the most important technique in horse breeding. Mares are most successfully bred at maximum receptivity, and this is at ovulation. Rectal palpataion of the uterus and its ultrasonics are 2 supplementary techniques. When ovulation absolutely correlates with the time of sexual intercourse with the stallion, one cover will do. Otherwise, returns make mating much more costly.

  5. Here are some suggestions:1/ External genital examination of stallion and mare, 2/ Breeding suitability examination of the stallion, 3/ Palpatation per rectum of complete mare reproductive tract, 4/ Ultrasonographic examination of mare reproductive tract (pregnancy diagnosis via palpation and ultrasonography) and 5/ natural cover or artificial insemination with cool fresh shipped or deep frozen semen.

  6. HormonesThe hypothalamus secretes gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete Luteinizing Hormone (LH) The hypothalamus secretes gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete LH and Follicle Stimulating Hormone (FSH). These hormones cause the growth and development of ovarian follicles. At the time of estrus, there is a massive release of luteinizing hormone that triggers ovulation, called the preovulatory surge.

  7. A corpus luteum (yellow body) develops from the remains of the follicle after the egg has been released. Once it has developed, it produces the hormone progesterone. It acts to inhibit GnRH release thereby reducing pituitary FSH secretion and thus prevents follicle maturation. As long as progesterone circulates in blood, estrus is prevented, e. g., pregnancy is so maintained if conception occurred.

  8. Regumate is synthetic progesterone named altrenogest given orally in vegetable oil. Each ml contains 2.2 mg altrenogest. Dosage is 1 ml/50 kg body weight for 10 consecutive days. Regumate can be used for 1/ inducing an ovulatory estrus, for inducing normal cyclical ovarian activity, 2/ Treatment of the mare in lactation anestrus, 3/for suppression of estrus either during prolonged estrus or in normally cycling mares and 4/ to control the cycle of breeding mares to allow efficient use of the stallion. The majority of mares will return to estrus within 8 days after the last oral dose of Regumate and will ovulate between 7–13 days later.

  9. Steps towards successful fertilization then foaling include: Edema begins 7-8 days before ovulation, peaking at 24-48 hours before ovulation and declining within 2 days of ovulation. Edema is found on both the day before and at ovulation with a 7.5 MHz ultrasound transducer.The hormones most commonly used to manipulate the mare's estrus cycle are progesterone and its analogues like altrenogest (Regumate). Estradiol is responsible for estrous behaviour in mares, and estrogen concentrations during estrus correlate well with sexual behavior and grossly observable changes in the reproductive tract. In contrast, progesterone inhibits estrus behaviour. Its rise in concentration leads into the next estrus cycle.

  10. Estrogen and prostaglandin For prostaglandin to affect an estrous cycle, it requires an active corpus luteum (CL). Progesterone started on the day of parturition, at regular dosage levels (150 mg/day IM for progesterone or 0.44 mg/kg per day orally for Regumate) for a period of 8 days, will usually result in the mare entering estrus 3 days after treatment ends.Progesterone and estradiol-17 beta combined is an injectable product given at the dosage level of 150 mg progesterone, 10 mg estradiol 17 beta per day IM.

  11. Successful breeding accounts for these factors: 1/ A healthy ova (egg).2/ Ova live 12 hours so must be exposed to sperm within this time.3/ Most sperm live 3-5 days in the mare that must contact the egg in the oviduct (tube connecting ovary & uterus) at this time.4/ Oviduct must be clear to allow passage of ova & sperm.5/ Fertilization must take place within the oviduct.6/ The oviduct environment must be suitable for egg, sperm & embryo.7/ Suitable uterine environment for embryo to implant on its wall must be available.

  12. Testes. A stallion's testicles each weigh 225-300 grams, averaging 4-5 cm long, 6-7 cm high and 5 cm wide. The testes produce sperm. Epididymis. The epididymis is attached to the testicle. The epididymis serves to transport spermatozoa out of the testes, concentrate it by absorption of water and provide a place for it to mature and be stored. Vas Deferens. The vas deferens, or spermatic cord, transports sperm from the tail of the epididymis to the urethra. The male reproductive tract

  13. The female reproductive tractOvaries:Mares typically have long erratic estrous periods in January, February and March. During the physiological breeding season-April through August-a large follicle develops during each estrous period and ruptures toward the latter part of the heat period, releasing an egg (ovum). The collapsed follicle is replaced by the CL which produces the hormone progesterone. If the mare does not become pregnant, the CL will have a lifespan of 12-15 days. If the mare becomes pregnant, several large follicles may develop on either ovary of the mare. These follicles may rupture or luteinize to form accessory or secondary CL as supplementary sources of progesterone.

  14. The Estrous Cycle The anovulatory season is a period of sexual quiescence extending from the last ovulation of the breeding season to the first ovulation of the next breeding season. Follicular activity is minimal December-February (Northern Hemisphere) with an increase in activity from March to May. During anestrus the ovaries are usually small and hard. Estrous cycle length and duration of the heat period is longest during the autumn months and shortest between April and October. The number of estrous periods is lowest in winter months. The number of small follicles (<20 mm) increases slowly during January to March. In the latter part of March, the number of small follicles decreases with a concomitant rise in the number of large follicles (>30 mm).

  15. The pituitary hormones involved in the estrous cycle are the gonadotropins: follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and estrogen. Estrogen stimulates 5-7 days heat in mares. LH causes the ovarian follicle to mature and ovulate. After ovulation the follicle is replaced by the CL which secretes progesterone needed to maintain pregnancy up to day 100. Both FSH and LH are under control of the gonadotropin-releasing hormone (GnRH), which is secreted by the hypothalamus gland of the pituitary. Seasonal anestrus is caused by a change in the feedback mechanism between the ovary and the hypothalamus involving a signaling system and cytokinines like inhibin and activin.

  16. The estrous cycle is divided into 2 periods. The follicular phase is the period during which there is rapid folliclular growth. The mare displays behavioral estrus for 5-7 days, then ovulation. The luteal phase begins with ovulation. During diestrus, the 15-17 days in between, the CL is formed and progesterone is produced by it. If the mare conceives, the integrity of the CL is maintained. Progesterone is secreted to maintain pregnancy for 40-50 days. Afterwards, a second rise of progesterone begins due to the formation of secondary CLs.

  17. At the beginning of the menstrual cycle, anterior pituitary gonadotrophic cells release FSH. This FSH travels to the ovary where it binds to immature oocytes, initiating their maturation. Such maturing oocytes or follicles make estrogen, which gives negative feedback to the pituitary to inhibit further FSH release. After about 14 days, one oocyte matures and releases a final burst of estrogen that causes the pituitary gonadotrophs to secrete both FSH and LH (luteinizing hormone). This "spike" of LH/FSH induces follicle rupture, leading to a decline in estrogen production. Cells in the ovary that contributed to earlier follicle maturation and now remain following ovulation develop into a structure called the corpus luteum.

  18. Breeding management proceedures Management procedures include:1/ teasing, 2/ rectal palpation, 3/ ultrasound examination, 4/ artificial insemination and 5/ artificial lighting. Teasing and estrous behavior record keeping are the most important parts of a successful breeding program. Positive signs of estrus include: posturing, tail raising, urination and eversion of the vulvar labia (winking the clitoris). Mares not in heat may kick, bite, swish their tail and pin their ears back when they think they are being assaulted. Even when they know you well, they may take shots at you when going in and out of heat !

  19. Separate records should include the year, the name, color and age of the mare, and the farm number. Assign individual mares a numbered neck band. Neck bands help in quick and accurate identification of each mare. Records should also identify the stallion the mare is booked to, the mare’s owner and previous breeding results. Of course records are kept on stallions including fees paid which can be big business.

  20. Sperm and artificial insemination Advantages of artificial insemination can include: 1/ Decreased transport costs, 2/ The stallion can be collected and his ejaculates frozen and 3/ There have been no limitations on the storage time of frozen semen. The disadvantages include: 1/ Wide individual freezing variability, 2/ The techniques are not standardized, 3/ After thawing, frozen semen has a shorter life span in the mare than fresh semen, 4/ The conception rates of artificial insemination with frozen semen are lower than with fresh semen. Conception rates of 60-65% can be reached.

  21. A ghost used in stallion collection substituting for a jump mare.

  22. A stallion is considered fertile when thesemen evaluation meets the following criteria: 1/ Volume 25-100 ml, 2/ Concentration 30-800 million spermatozoa/ml, 3/ Progressive motility 60-100 %, 4/ Morphology 70-80 % normal and pH 7.4-7.6.Let us say that semen has been diluted and deep frozen as in liquid nitrogen into 200 straws. Cost for managing this ejaculate is say $ 600. Then each straw costs $ 3.Embryo transfer and testtube growth of oocytes (ova) has been performed with very low success levels. A mare could have 25 plus foals by transfers (transplants) and nuclear transplants can be performed as in cloning.

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