Featured Article (December 2003)

Top Ten Steps To Get Your Mare Pregnant and Keep Her That Way

Many aspects of animal husbandry, farm management, preventive veterinary medical care, and reproduction go 'hand-in-hand' toward producing a successful pregnancy and positive foaling outcome. To detail them all would take more time and paper than this volume of the Virginia Horse Journal has to offer. With this in mind, I will give what I consider to be the cornerstones of a good breeding management program, whether it be for one mare in your care or an entire band of broodmares on a large breeding farm.

10 Make sure her body condition is average or above.

Nutritional management of the broodmare should be to maintain her in an above average body condition (e.g., score of 6 on a scale of 1-10). Mares foaling in better than average body condition, and maiden and barren mares that have average or above average body condition scores conceive sooner than mares in less than average (i.e., thin) body condition. Obese (aka, fat) mares or those with body condition scores > 8 (scale 1-10) tend to have more difficulty conceiving. Some obese mares may warrant investigation for hypothyroidism (low thyroid hormone levels).

9 Make certain she is cycling and ovulating.

Reproduction for most mares is highly seasonal. The peak of their reproductive performance and efficiency occurs around the summer equinox (or June 15th) in the northern hemisphere. Mares will have a significant spring time transition period between winter (not cycling or anestrus) and regular estrous cycle activity (physiologic estrus). During this transition they may show erratic or prolonged behavioral signs of heat (estrus, or tease "in" to a stallion), but frequently do not ovulate, or ovulate only after a prolonged time of showing heat. This is the wrong time to breed her. Just because she is showing behavioral signs of receptivity to the stallion's amorous approaches, does not mean she is ready to breed successfully. She must also have a large (Graafian) follicle that is nearing ovulation for a breeding or insemination to have any chance of inducing conception. Three breeding management methods are available to assist her through these transitional times more quickly: (1) an artificial lighting program, (2) hormonal therapy (e.g., gonadotrophins, progestagens or progesterone), and (3) patience. Consult your veterinarian and discuss the options that may work best for your situation.

8 Be sure her perineal conformation is adequate.

The mare must have an effective conformational barrier to prevent fecal (bacterial) contamination from ascending the reproductive tract and causing an infection and/or abortion. The first anatomic line of defense is the conformational relationship between her vulva and anus (rectum). Your veterinarian is the best resource to provide advice on this, but a quick and easy test is to part the lips of her vulva (being careful not to get kicked). You should be able to expose at least an inch of the pink, glistening mucous membrane on either side before the mucous membrane contact or seal formed by each side gaps open. Another key ingredient is the angle formed between her anus (rectum) and lips of the vulva. A desirable angle should be near vertical. Improving her body condition, causing more body fat to be stored in the perineal area, can help a mare with borderline conformation. Surgical correction by your veterinarian (e.g., Caslick's surgery or vulvoplasty) is the preferred and most effective means of assisting mares with poor perineal conformation.

7 Know that her internal reproductive tract is healthy and ready for conception.

Prior to breeding, your mare should be examined for health and well-being of her vagina, cervix, and uterus. This can involve many different techniques. The simplest and least invasive is a rectal exam with ultrasound of the reproductive tract. While rectal palpation alone is good, it is not as discriminating as an ultrasound, which can detect a small accumulation (or pocket) of fluid in the uterus, and cysts in the lining of the uterus (endometrium). Either of these findings may indicate an abnormality (infection or degeneration) requiring further diagnostics. A visual inspection (vaginoscopy) of the vagina and external of the uterine cervix can determine the health and well-being of these portions of the reproductive tract. Any sign of inflammation, discharge, or bleeding would be cause for concern. Scarring of the cervix from a previous foaling injury can be devastating to the continued success of the mare as a breeding prospect. The next step may be collection of a cytological sample from the uterus. This is evaluated for presence of white blood cells, which indicate inflammation is present in the uterus. When found they support the need for a culture of the uterine fluid for bacterial growth and identification. A culture of the uterus by itself is often very misleading, and should always be supported by other evidence that an infection is present. Besides a cytological analysis, another means of determining if infection or inflammation is present in the uterus is with a biopsy sample of the endometrium, the pregnancy supporting lining of the uterus. When obtained and interpreted appropriately, a uterine (endometrial) biopsy sample can also provide useful predictive (prognostic) information as to whether the mare is capable of maintaining her pregnancy once she conceives.

6 Have a reasonable assurance that the stallion's sperm is of acceptable quality.

It makes little sense to breed a mare to a stallion or inseminate her with his sperm, if his semen quality is suspect or inadequate. Have the stallion examined for breeding serviceability if possible, or request the stallion owner/manager send you a copy of his reproductive performance record. The most useful statistics to obtain would be conception rate per cycle, and breedings or inseminations per pregnancy. A good stallion will have greater than 60% conception rate per mare-cycle, and less than two breedings or inseminations per mare-conception. If this information is not available, have your veterinarian evaluate the stallion's semen quality prior to insemination (for both fresh, extended, cooled, shipped semen and frozen-thawed semen). Sperm motility is commonly used to judge semen quality, but be aware that this is only one parameter of semen quality. The number of sperm inseminated that are alive (motile) and morphologically normal (normal-shaped) is a better indicator of potential fertility. In the case of frozen-thawed sperm, even these two parameters have proven less than adequate as an indication of semen quality and ability of sperm to fertilize an egg.

5 Time the breeding or insemination appropriately.

Once ovulation occurs the ovum (egg) of the mare has a 4 -12 hour window of opportunity to become fertilized by any available sperm in her reproductive tract. The breeding or insemination usually has to occur sometime prior to ovulation, how soon is stallion dependent. Some stallion sperm have the ability to survive for days (sometimes weeks) in the mare's reproductive tract. Other stallion's sperm may only last for hours before they all die or lose the ability to fertilize an egg. A good rule of thumb is that for natural service, cover the mare beginning on the second or third day of her heat and then every other day until she is no longer receptive. For artificial insemination, it is best to have the mare examined by your veterinarian for follicle development. Once the follicle is of sufficient size (usually greater than 35-40 mm in greatest diameter) and is softening, it is time to inseminate her within 12-24 hours. It takes a great deal of experience and training to be good at predicting ovulation in the mare. The optimum time to inseminate with fresh, extended, cooled, shipped semen is 12-24 hours prior to ovulation. The best time to inseminate using frozen-thawed semen is 4-6 hours prior to ovulation. Inseminations (or breedings) that occur after the mare ovulates can result in conception, but timing must be no later than the first 4-12 hours after she has ovulated. Anytime after that, she is unlikely to conceive. Or if she does conceive, she is likely to lose the embryo due to abnormal development (early embryonic death). Breeding or inseminating the mare after the window of opportunity for egg fertilization wastes semen and exposes the mare's uterus to unnecessary risk of infection.

4 Determine that she is either pregnant or not pregnant at the earliest opportunity.

It is not good breeding management practice to wait 18 or more days to see if she teases back into heat again. The best reproductive management dictates that the mare be examined by rectal palpation and ultrasound between days 14 -17 after ovulation. At this time, your veterinarian can determine if she is pregnant, and whether she has potentially conceived twins. Twin pregnancy in the mare must be eliminated early to allow her the best chance to maintain her pregnancy with at least one embryo, and prevent a later, probable abortion with both. If she is not pregnant, you can prepare her for the opportunity to be bred or inseminated again within the next 4-7 days. Because mares have an inherently high incidence of early embryonic loss (in some cases as high as 20%), it is advisable to have her re-examined every 7-10 days until she is at least 45 days in gestation and considered safely in foal.

3 Provide an effective wellness program during gestation.

Once you have invested all this time and effort into getting her pregnant, why waste it by dropping the ball? Consult with your veterinarian regarding a specific preventive health care plan to safeguard her pregnancy and prevent infections from causing an abortion, or weakened foal at birth. The mainstays of such a program will include: (1) nutrition for gestation to support effective fetal growth and development; (2) immunizations to prevent her from becoming infected with viruses (e.g., Equine Herpesvirus) or bacteria (e.g., Streptococcus equi) and to boost her colostum (first milk) with appropriate antibodies for the protection of her foal in the first 60-90 days after foaling; (3) deworming; and (4) isolation or quarantine. The latter is good management practice to invest time and effort into. If you can prevent your pregnant mare from being exposed to new or 'outside' horses, the risks of her coming into contact with a potential infectious agent is greatly diminished. This is often more effective than immunizations, which by themselves are seldom 100% protective.

2 Prepare in advance for her foaling.

Review books on foaling management in your local library, or go on the internet and search for relevant resources. Being an informed mare owner and knowing what to expect helps you to identify when things are going wrong much earlier. This can make the difference between life and death for not only your foal, that you've waited for these past 11 months, but maybe also for your mare! Remove mares from Fescue grass (pasture and hay) as much as 90 days prior to their expected foaling date. Check with your veterinarian to be sure that a supply of domperidone is available. This is a specific and effective treatment for pregnant mares suffering from the mycotoxin in many Eastern US Fescue grass pastures and hays. Observe your mare for signs of udder development and lactation. There should be some development occurring at least 2-3 weeks in advance of the foaling date in most mares. Too early udder development with respect to her due date can be cause for alarm, call your veterinarian. Too little udder development can mean that her breeding date was wrong, or she aborted unobserved in the pasture, or that she has been exposed to Fescue mycotoxins. Have her examined. There are several methods available to assist you in determining when she is likely (or unlikely) to foal. I highly recommend the use of the FoalWatch® test kit from CHEMetrics, Inc., Calverton, VA (for technical and ordering information call 1-800-356-3072 or Fax 1-540-788-4856). This test measures calcium changes in the pre-foaling mammary secretion (colostrum). It can be very useful in determining when the mare is least likely to foal, and when she is approaching readiness for birth.

1 Enjoy the fruits of both your 'labors.'

Life is a journey. Enjoy it! There may be detours, pitfalls, and flat tires along the way, but there are also beautiful vistas, exhilarating twists and turns, breathtaking sunsets (and sunrises), and the joy of knowing you had a hand in helping that precious creature, your foal, get a good start in life.