Breeding

Julie A Grohs, DVM

                It's a big commitment emotionally and financially to decide to breed your mare and produce a foal, so preparing your mare in advance of breeding season will help to improve your chances of success in this endeavor.  The first step toward breeding your mare is educating yourself about the normal reproductive cycle of the horse. 

                Mares are seasonally polyestrous, meaning that most mares have estrus cycles throughout the spring and summer months and are anestrus, or without estrus cycles, through the winter.  Regulation  of this cyclic activity is primarily by photoperiod (increasing number of daylight hours in the spring stimulates mares to start cycling) and partially by nutrition and temperature.  Mares are often stood under lights in late winter to stimulate an early return to cyclic activity for early season breeding.  The general recommendation is to use the equivalent of a 100 watt light bulb in a 12X12 stall for 14 to 16 hours per day.  It requires 6 to 8 weeks of this regimen to bring an anestrus mare into normal estrus activity with ovulation.  There is always a transitional period in which follicles develop but do not ovulate, and this may result in longer or shorter heat periods than normal. 

                The normal estrus cycle of the mare is about 21 days in length.  Mares usually remain in heat (estrus) for 4 to 7 days and are out of heat for the other 15 days.  Heat cycles often vary individually but mares tend to be consistent in the number of days in and out of heat from cycle to cycle and year to year.  Mares will ovulate, or release an egg from a follicle, about 24 to 48 hours before they go out of heat. 

                Detection of the heat cycle of the mare is a critical step toward successful breeding.  Most mares exhibit behavioral changes when in heat, though this behavior may only be obvious in the presence of a stallion.  "Teasing" mares is a method of detection used by breeders to determine when a mare is in heat.  Evaluating the response of the mares to the stallion at the teasing rail helps to predict the best time to breed the mare.  This behavior does not predict ovulation however.  Ovulation or impending ovulation can be detected by rectal palpation or more reliably by ultrasound.

                Successful breedings rely on sperm reaching the ovulated egg at the correct time.  To improve the chance of a successful breeding mares should be covered or inseminated 0 to 48 hours prior to ovulation when bred naturally or with fresh semen, within 24 hours with transported, chilled semen, and less than 24 hours with frozen semen.  Minimizing the number of  breedings per cycle is actually more successful than continual inseminations at inappropriate times.  This reduces contamination,  labor, and cost.

                How do we know where and when the egg is most likely to be ovulated?  At ovulation, an egg is released into the uterine tube where fertilization can take place in the presence of viable semen.  The fertilized egg, or embryo, enters the uterus at 5 to 6 days post ovulation and wanders throughout the uterus until day 16.  At this time the embryo implants into the uterine lining.   Endometrial cup cells are responsible for progesterone production and form by day 35 to 36 and persist until  day 130 of pregnancy.  At day 35 to 40 microcotyledons have formed as well and by day 100 the placenta of the fetus is fully functional and able to produce its own progesterone.

                  We can recognize pregnancy in the mare by days 12 to 14 with transrectal ultrasound and by rectal palpation by days 21 to 25.  Occasionally blood progesterone levels are indicative of pregnancy in the mare.  The length of gestation in the horse is an average of 335 to 342 days. 

                With this very basic understanding of the reproductive cycle of the mare we can now discuss more specific recommendations for preparing for breeding season.  The history of the potential broodmare is very important.  Is she currently pregnant or nursing a foal?  Have you attempted to breed her in the past?  Did she conceive, and if so, did she carry the foal to term?  Is she a maiden mare who has never been bred?  Previous information on foaling data, surgery, infections, abortions, and cycling patterns are valuable pieces of information.   What is the mares athletic history and what is her general health history?  The answers to these questions may have a bearing on her reproductive performance, and prior knowledge of problem areas will save time and money. 

                The next step is a general physical and reproductive exam of the mare by a veterinarian prior to breeding.  It is a good idea to have current vaccinations and to be sure of the general health and nutritional status of the mare prior to breeding.  Your veterinarian can evaluate the mares weight and condition, check her teeth, evaluate your deworming program, and identify any problems that may interfere with successful breeding.  If you will be transporting your mare to the stallion, realize that most breeding managers require current vaccinations, a current Coggins test (for Equine Infectious Anemia), and results of an intrauterine culture.  These procedures are also recommended if your mare is to be bred by artificial insemination with transported semen.  The reproductive exam, which evaluates the activity of her ovaries and the condition of her uterus, cervix, and vagina, is best performed while the mare is in heat.  The exam also includes an evaluation of the external reproductive anatomy; does her conformation predispose her to wind-sucking or other abnormalities, are her mammary glands of  normal size and shape, and has she suffered from mastitis? An internal reproductive exam is usually performed by ultrasound or rectal palpation,  checking for ovarian structure and activity, uterine structure and abnormal fluid, cervical structure. Finally, a vaginal exam should be performed to evaluate the appearance of the cervix and vaginal vault.  This is when an intrauterine culture and swab for cytology can be collected.  In some situations it may be helpful to perform further reproductive diagnostic tests such as endometrial biopsy, endoscopy, hormone studies, and even cytogenetic or DNA studies.  The need for these advanced procedures arises when there are problems getting the mare to conceive and/or maintain a pregnancy. 

                Thankfully, Mother Nature has provided the mare a highly developed breeding capacity.  Most breeding attempts prove successful, and eleven months later you can expect a new foal in your barn.  It is important and beneficial to continue giving our mares the best quality care and y addressing any reproductive abnormalities or problems prior to breeding you can enhance the next seasons foal crop. Good luck!

            Drs. Joe and Julie Grohs are 1981 graduates of Washington State University, College of Veterinary Medicine in Pullman, WAS. They came to Alaska in the summer of 1981 and established the Alaska Equine and Small Animal Hospital. Both doctors have a special interest in horses. In 1985 they built the present hospital facility with a specialized surgical suite for horses and indoor hospital stalls. The facility is equipped with state of the art diagnostic and therapeutic equipment and is located at 21236 Birchwood Rd. in Chugiak.  Phone (907) 688-9303