Chapter 6


Pregnancy begins with delivery of the sperm to the ovum. There are several ways in which sperm can be delivered to the egg, including:


Management of the teaser depends on the type and number of teasers available on the farm; for further discussion, see p. 77.

Each mare is an individual, and her specific teasing and estrus behavior must be learned in order for teasing to be properly utilized in a reproductive program. Teasing behavior will also change with the season. Mares will often be ambivalent to the teaser or stallion during winter anestrus, with signs of good standing heat increasing during the transitional period, becoming most reliable when normal cyclicity is occurring and then decreasing again during the fall transition.

Breeding by natural service1

On small studs and in some breed associations – most notably the Thoroughbreds – natural service is the only acceptable method of breeding. If natural service is utilized, the stallions and mares must be carefully managed.

The goal of any breeding program is to breed each mare once only, with all mares conceiving from that breeding.

The advantages of natural service are:

The disadvantages of natural service are:

Natural service requires that the stallion physically mates with the mare.

Mares may not be receptive until they become accustomed to new surroundings. A strange environment or unusual circumstances (handler changes, etc.) can have a marked effect on the mare’s display of estrus.

The facilities

• The breeding shed should be large enough for movement of the mare, the stallion, and their handlers (see p. 16).

• There should be good, firm, nonslippery footing (Fig. 6.1).

• There should be an exit route for both the mare and the stallion should problems arise.

• The mare should be hobbled or breeding boots put on her rear feet and a twitch applied (Fig. 6.2).

• The tail can be tied to one side if quick-release knots are used both on the tail and around the neck of the mare, so that the tail can be released easily if the stallion should become entangled. Otherwise, the tail can be allowed to hang.


• One person should handle the mare.

• A second person should handle the stallion and a third person should assist the stallion during intromission (Fig. 6.4).

image Mares that have a ‘breeding stitch’ (not a Caslick’s suture, see below) in place at the time of mating should have this stitch moved out of the way by the same person who assists in intromission. A breeding stitch is simply a suture that is inserted to restrain the vulvar lips and limit vulvar flaccidity and the risks of damage to the Caslick site. This will prevent any injury to the stallion’s penis by the stitch. In the event that the vulva is damaged during service it is routinely repaired immediately afterwards.

image The same person can keep a hand on the base of the penis to palpate for urethral pulsation and confirm that ejaculation has occurred (Fig. 6.5).

image Some stallions do not like having their penis handled in any way, making this third person’s job unnecessary.

Preparation of the mare for breeding

i. When the mare is found to be receptive and ready to be bred, her tail should be wrapped and the perineum washed with mild soap and warm water and rinsed thoroughly (Fig. 6.6).

ii. Mares that have had a previous Caslick’s operation (vulvoplasty; see p. 184) should be examined to determine if there is adequate area for penetration without the risk of tearing the vulva or injuring the stallion’s penis.

Preparation of the stallion

i. At the start of the breeding season, the penis, fossa glandis and urethral diverticulum should all be cleaned carefully. Suitable swabs, etc. will be required for disease control.

ii. The stallion’s penis should be washed with warm water prior to breeding (Fig. 6.7).2,3

iii. After covering the mare, the penis should be washed again to rinse any contamination derived from the mare.

Minimal contamination breeding technique


Artificial insemination has become a normal procedure in stud medicine. However, there are still major problems associated with both the ethical aspects (it is not an accepted procedure in the Thoroughbred) and the relatively poor cryoprotection of sperm in frozen semen compared with other domestic species.

There are significant advantages in the use of artificial insemination, but there are also disadvantages. Artificial insemination includes the use of:

The methods commonly used for semen collection in modern stud practice are outlined on p. 62. Although there are other, cruder, methods (such as the use of vaginal sponges), these are becoming less acceptable as the technology of semen collection and use improves. It is important to realize that the correct collection of semen, precise handling of the ejaculates and the management of the mare are all vital if first conception pregnancy rates are to be kept acceptably high.

Most breeding programs that use artificial insemination incorporate the administration of an ovulatory agent and repeated ultrasonographic examinations of the reproductive tract to time ovulation. Both should be used in breeding programs if mares are to be bred with cooled or frozen semen. If the stallion resides on the farm with the mares, it is not uncommon to breed the mares with fresh semen every other day until they stop exhibiting estrous behavior. This breeding protocol is not recommended if the mare has a history of persistent mating-induced endometritis. The technique of artificial insemination is similar with fresh, fresh-cooled or frozen semen with the exception of the delivery system. Most commonly, mares are bred with an artificial insemination pipette attached to a syringe when fresh or cooled semen is used. An artificial insemination gun or a flexible catheter for deep inseminations into the uterine horn may be used with frozen semen.

Use of an ovulation-inducing agent

• Ovulation can be timed with reasonable accuracy by administering either human chorionic gonadotropin or deslorelin.

• Most mares are given the ovulatory agent when the dominant follicle is 35 mm in diameter (normally on the second or third day of estrus) and endometrial folds are present in the uterus.4

• The size of the follicle affects the mare’s ability to respond to human chorionic gonadotropin. Most mares will not respond if the dominant follicle is smaller than 35 mm. Some Warmblood mares will not respond with a 35-mm follicle, especially if it is present on the first day of estrus. In these mares, it may be best to administer human chorionic gonadotropin on the second or third day of estrus when the dominant follicle is 38–45 mm and there are prominent endometrial folds.

• The majority of mares ovulate 36–48 hours after intravenous administration of 1500–3000 IU of human chorionic gonadotropin.

• Deslorelin, a synthetic gonadotropin-releasing hormone agonist, designed as an implant, under the same criteria, induces ovulation in mares on average 41–48 hours after it is inserted.5

• The response to deslorelin does not appear to be so dependent on follicular size. It may be given when the dominant follicle is as small as 30 mm in diameter.

• Some mares that are implanted with deslorelin have a prolonged inter-estrous interval between 28 and 45 days if they do not conceive. Removal of the implant between 42 and 48 hours after it was inserted prevents this problem from occurring. Placing the implant in the submucosa of the vulvar lips facilitates implant removal.

Ultrasonographic changes in the reproductive tract

Ultrasonographic examination of the reproductive tract during estrus is extremely useful in timing ovulation because estrogen causes the uterus and follicles to undergo characteristic ultrasonographic changes.

As the mare nears ovulation, the follicle changes from a round to a tear-drop (pear) shape and the rim of the follicle becomes hyperechoic (appearing whiter).6

Jun 18, 2016 | Posted by in EQUINE MEDICINE | Comments Off on MATING
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