By Heidi Smith, DVM

In the Arabian industry, many breeders are faced with decisions about breeding older broodmares. Some breeders are concerned with preservation of older lines, and in many cases, preservation breeders find themselves faced with older mares that have been out of production. In other cases, older mares have simply been good producers and breeders feel that these mares should continue to contribute their genetic legacy to future descendants. Some astute new breeders try to get a head start by selecting older mares who have produced well. No matter what the reason, there often come times when we are faced with the prospect of breeding an older mare. When this is the case, we have to consider the odds of getting the older mare in foal and safely through parturition, as well as what extra effort or care may be necessary to maximize success in the endeavor.

One of the first problems encountered when breeding the older mare is that as mares age, their "biological clocks" tend to run more slowly, making them later to begin cycling in the spring, causing them to be less fertile in spring cycles, and sometimes prolonging fertility into fall months. One of the first things that I advise my clients with older mares is to realize that they may well not be getting early foals for halter futurities and to discard any notions of when a "breeding season" should be. If the older mare is truly worth breeding for her genetic contribution, it really becomes immaterial when her foals are born. It has been my experience and that of many other breeders and veterinarians that mares in their late teens and early 20's often will conceive best in late summer or even in the fall. I've also found the cycles of older mares far more difficult to manipulate with hormones; one often loses the luxury of being able to "schedule" cycles as one can frequently do in younger mares. This can make it difficult to fit the breeding of an older mare into the other realities of life, such as the owner's show schedule, a strict semen shipment schedule, etc.

One also has to evaluate each older mare as to her breeding history and breeding condition when making decisions about breeding. Certainly if the mare is genetically valuable to the breeder, one may well try to breed even if the odds are not good. However, one must take a realistic look at the odds. Clearly, the older the mare, the poorer the odds. However, many mares (especially Arabians) DO reproduce well into their 20's. What are some of the red flags that we look for?

One of the first things I want to know when evaluating an older mare as a breeding prospect is what her reproductive history has been. Older maiden mares can often present a real challenge. The odds of getting a maiden mare in foal begin to decline as her age gets into double digits. By the time she has reached her late teens, her odds of conception are poor, even if no valid medical reason for reproductive failure can be found. Nonetheless, one runs into the older maiden from time to time who gets right in foal on the first try, so if the mare is valuable to you, she may still be worth some effort. On the other hand, older mares who have been in production somewhat regularly are often a fairly good risk. The more recently they have foaled, the better their odds.

The next part of the mare's history that I like to look at is how easy she has been to breed in the past. Obviously, mares that have been difficult breeders simply become more difficult as the years progress, and are apt to become infertile earlier than mares who conceive and carry easily. However, don't mistake a good breeding history for a sure thing. Mares are not like robots--they may not simply continue to conceive and foal year after year just because they "always have." Even the easy breeders will reach a point where it takes some care and help to get them in foal. The more history one has about a mare's breeding past, though, the easier it is to pinpoint areas where she may need help.

 

With older mares of unknown history or older mares who begin to present breeding challenges, the first thing I look at is overall health. Before even attempting to breed, they need to be on a good nutritional plane. Older horses frequently have difficulty processing feed, and hence are deficient in micronutrients that are sufficient in the diet for their younger counterparts. One of the primary reasons for this is poor dental health. I like to see all broodmares receiving some level of dental care, but it becomes imperative in the older mare to insure that she has a good mouth and is capable of completely grinding feed. In mares who have received regular maintenance or who don't have particular dental problems, this may be achieved by annual or semi-annual dental maintenance. In mares who have serious dental problems, though, achieving a good mouth may take repeated visits from a veterinarian well-versed in dental care or an equine dentist recommended by your veterinarian. In older horses, the eruption rate of the teeth begins to diminish. Because of this, often not as much can be accomplished on any one dental visit; it may take visits every two or three months to get the mouth right. In extreme cases, the older mare may have such serious dental problems that it is not possible to achieve a good grinding surface; in such cases, one must supplement her with soft, palatable feeds that can be digested with minimal chewing and that still meet her nutritional requirements.

Once one has dealt with the dental care in the older broodmare, one must be sure to provide adequate nutrition. Good rations are built around roughage, and if the older mare has difficulty holding her weight, she should have high-quality hay free choice. Various commercial senior rations are often helpful. Not only must the older mare have sufficient calories and a well-balanced diet, but she should also receive a vitamin-mineral supplement that is appropriate for geriatrics. Older horses often have a more difficult time absorbing such nutrients as zinc and selenium.

In addition to good overall health, the health of the mare's reproductive tract should be determined. If at all possible, have her evaluated the fall prior to attempting to breed her. If this is not practical (such as if you just acquired an older mare), have a breeding soundness exam done as soon as possible. For the older mare, an exam should include a culture, an ultrasound, and a thorough rectal palpation, as well as an evaluation of her external genitalia. Older mares are more apt than younger ones to have tipped vulvas, which can cause continual contamination of the vagina (and hence on into the cervix and uterus) with fecal material. (This can also be due to poor pelvic conformation.) The older uterus is more apt to have poor tone, uterine cysts, or intrauterine fluid. Make sure that the ovaries are of sufficient size to be functional.

If the mare has uterine cysts, uterine fluid, or any sort of uterine infection, appropriate therapy for the problem should be instituted. With intrauterine infections, repeated intrauterine infusions or lavages with saline containing an appropriate antibiotic is indicated. In recent years, it has been found that following infusions or lavages with small systemic doses of the hormone oxytocin is very beneficial in aiding the uterus to clear excess fluid. This also helps in clearing the infection. Treatment is best accomplished while the mare is in heat, so that the cervix is open. Follow-up cultures should be performed in infected mares to make sure that the treatment has actually cleared the infection. In mares with tipped vulvas, your veterinarian may want to do a short Caslick's repair that limits contamination through the vulva but still gives the veterinarian access to the vagina for necessary treatment. Keep in mind that the older uterus is often more susceptible to infection (hence easier to reinfect) and has less ability to clear contamination without help.

Many people are frustrated when they have worked to clear up an intrauterine infection and then the mare does not get promptly in foal. If infections have been long-standing, there is often damage to the endometrium (lining of the uterus) that takes time to heal. In some cases, mares (especially older mares) may lose a year or more in production due to the damage of a long-standing infection. Occasionally, a long-standing infection will cause sufficient damage to render a mare completely unbreedable. Sometimes the level of damage can be assessed by biopsy. Don't hasten into a biopsy, though, until the mare has had some time to heal.

 

We treat intrauterine fluid very much the way we treat infection, with lavage or infusion followed by oxytocin. However, fluid without infection can usually be cleared with fewer treatments. If mares are prone to accumulation of fluid, we want to take special care at breeding time to treat them for the problem.

Intrauterine cysts are a frequent finding in older mares. If they are few and small, they often don't interfere with reproduction at all. However, if there are many cysts, or if they are large or complex, treatment may be necessary. We've had good luck with many such mares treating them with infusions of 20 ml DMSO in 40 ml of saline. We repeat this daily for 3 to 4 days during a heat cycle, and then reassess the mares on the following cycle. Sometimes treatment must be done for more than one cycle. If this treatment is unsuccessful, alternate treatments for cysts include their removal with laser (very expensive, and very few facilities have the appropriate equipment) or mechanically (must be done by a veterinarian extremely familiar with the procedure).

 

So your older mare has either presented with a suitable breeding soundness exam or has had her problems treated. How can we manage the breeding procedure to maximize the chances of getting her in foal? Two factors are very important. First, she is less likely to be able to get rid of the contamination of breeding (which includes not only bacteria, but also excess fluid, excess sperm, etc.) than is a younger mare. Second, her uterus and oviducts are less apt to provide a hospitable environment to sperm than is the reproductive tract of a younger mare. To minimize these problems, we want to cover the mare as few times as possible (preferably only once) to minimize the amount of contamination with which she has to deal, and we want to cover her as close to her actual ovulation time as possible.

In the younger mare, it can usually be assumed that sperm will live anywhere from 48 to 72 hours or longer in the oviduct (which is where conception actually takes place) and that the mare's ovum will survive anywhere from 6 to 12 hours after ovulation prior to being fertilized. Consequently, we can often maximize breeding success simply by breeding her every 48 hours when she is in heat, and we can even sometimes get a conception after ovulation. In the older mare, we want to ensure that sperm is waiting for the ovum as soon as ovulation occurs, to negate any survival problems of the unfertilized ovum. However, we also want to make sure that there is live sperm present at the time of ovulation. In the older mare, I strongly recommend following the heat with daily palpation, so that breeding can be done as soon as the veterinarian feels that ovulation is imminent. One may also want to increase the odds of successful ovulation with the use of such hormones as HCG (human chorionic gonadotropin) or Ovuplant. Ideally, I like to breed the older mare within 12 to 24 hours of pending ovulation. Artificial insemination is also a useful tool in those older mares that are prone to infection or have difficulty clearing fluid.

A lot can be done to help the older mare around breeding time, too. If she is one that is prone to accumulation of fluid in the uterus, this can often be managed with small doses of oxytocin daily during the heat prior to the actual day of breeding. After breeding, oxytocin can be administered to help the uterus with transport of sperm into the oviduct, as well as repeated doses a few hours apart to help the uterus to expel excess fluid. Intrauterine lavage or infusion can also be done as early as 4 to 8 hours after breeding, since the viable sperm are already well up into the oviduct by this time. Since the fertilized embryo does not descend from the oviduct to the uterus until five days after conception, repeated lavages in the first few days following breeding can be helpful, too. This is a particularly useful therapy in mares that are prone to infection. Once again, following any such treatment, oxytocin is helpful to make sure the uterus expels unnecessary fluid.

If you are not in a hurry with your younger mares, you may choose to take a wait-and-see approach after breeding to see whether they come back in heat or not the next time they are due. With older mares, though, I do recommend doing an ultrasound exam by day 16 to determine if the mare is pregnant; if she is not, and if she has excess fluid in the uterus, you want to get a leg up on treating her on the next cycle. A word of caution is in order here, though; occasionally a mare will have a silent second ovulation a few days after the first one, and hence will actually have a conception date later than expected. (I also feel that older mares are simply prone to not having the fertilized embryo begin development quite as quickly as younger mares.) If I do not find a pregnancy in an older mare at day 16 on the ultrasound AND if the uterus has tone that is suggestive of pregnancy, I will WAIT before instituting any kind of therapy and recheck her in about a week. I've had too many older mares fool me and show what looks like a 16-day pregnancy at day 22 or 23 and go on to have normal pregnancies to want to be too hasty. This is a judgment call that should only be made by a veterinarian experienced in equine reproduction. Don't assume, though, that the older mare is in foal simply because she does not return to heat at the predicted time. She may be cycling irregularly, or may have a problem that needs attention.

With the older mare, conception may be only half the battle. Especially if the older mare has a history of conceiving and then resorbing the embryo, one may need to follow the pregnancy and consider the possibility that the mare may not be producing enough progesterone. I pay close attention to uterine tone when doing the 16-day ultrasounds on bred mares and make it a policy to test any mares whose tone I feel is not normal, since progesterone is one of the factors in providing uterine tone in pregnancy. (I don't routinely put mares on a progesterone supplement [altrenogest, marketed as Regumate] after breeding unless they have a history of not being pregnant at 16 days and I don't find other medical reasons.) Some mares do not produce enough progesterone even during the initial stage of pregnancy, and those can only be diagnosed through testing. However, there are two times that are particularly at risk for lowered progesterone levels during pregnancy. The first is at around 35 to 42 days, when the corpus luteum (the structure formed on the ovary from the remains of the ovulated follicle that produces progesterone) is declining and the uterus is forming structures called endometrial cups, which take over the production of progesterone. If the corpus luteum declines too rapidly or the endometrial cups don't form quite soon enough, the progesterone levels will drop and pregnancy can be lost. The second risk period is between 90 and 150 days, when the endometrial cups decline and the placenta takes over the production of progesterone. Either of these stages can be risky in the older mare. History of pregnancy loss at either of these times is good reason to test progesterone levels, and with an older mare without a history, testing may be worthwhile in any event. If low progesterone is a problem, supplementation is safe and effective.

There are other causes of pregnancy loss in the older mare that are more frustrating. One is uterine insufficiency. This occurs when the uterus simply cannot support the demands of a growing pregnancy. The problem varies in degree, ranging from mares who simply cannot carry a pregnancy past a certain stage down to mares who carry to term but have small or weak foals. The latter mares can often be helped through late gestation with extra vitamin and mineral supplementation as well as products such as MSM that provide dietary sulfur as well as apparently having some effect on the ability of the uterus to transport nutrients into the placental circulation.

Many people ask about embryo transfer in older mares that are not able to conceive. This can sometimes be done in mares that are continuing to have normal cycles, but I would like to interject a word of caution in investing in the procedure for extremely aged mares. In old mares, there is often sufficient chromosomal damage in the ova that even if conception occurs and the embryo is implanted into a healthy recipient mare, the embryo often still dies and is resorbed at 30 to 40 days. It is now thought that this may be the reason for early embryonic death in many of the older mares, rather than the mare's inability to carry the pregnancy.

Once you are successful in your breeding endeavor, you are faced with your older mare pregnant and approaching term. Parturition in the older mare is another time for diligence. A few older mares will carry their pregnancies just fine, only to suffer from uterine inertia when they go into labor. It pays to keep a close eye on the older mare that is near foaling, as she is much more apt to need a gentle helping hand than are her younger herdmates. Don't be afraid to give the older mare some foaling assistance, and do have your veterinarian alerted to the fact that she is ready to foal, just in case.

Many older mares seem to be truly thrilled with motherhood, which in itself is rewarding to watch. But the real payback in successfully breeding the older mare is having her genetic heritage to carry on into the future.

Heidi Smith, DVM PO Box 103 Tendoy, ID 83468-0103 Phone: (208) 756-6060