A broodmare which fails to conceive or carry a foal to term can be an emotional and financial liability. For the backyard breeder, the liability might be primarily emotional, when that special mare you wanted to produce your next trail horse or hunter simply doesn't do so. For the commercial breeder, there might be emotional trauma, but more importantly for him or her, the economic liability can be significant.
It costs an estimated $4,000-$5,000 per year to maintain a broodmare at a top facility in a place like Kentucky. That is not small change for a mare which has, as her prime function in life, the bearing of offspring for commercial sale or private athletic use.
There can be a multitude of reasons why a mare doesn't conceive or carry a foal to term, and some of them have to be laid at man's doorstep. Mares in the wild which don't bear young travel with the band until the end of their days, but they don't leave behind a legacy of more problems through their offspring. It is Nature's way of culling, just as it is when a horse has weak hooves and falls prey to a predator. Only the fittest survive to produce replacements.
Man has not been content to accept Nature's edict, mostly for economic reasons. If a mare has been a superior performer on the racetrack or in the show ring, for instance, the owner's goal when the mare has retired from competition, or even before, is to raise a foal that will be of equal or greater ability. The fact that the mare tells us through her physiological response that she is nearly incapable of reproducing doesn't deter us. We turn to science to manipulate her system to achieve a pregnancy that will be carried to term.
Science has provided many answers and tools in recent years, but with these positives come some negatives. Yes, we often can obtain a foal, but we might be continuing an inherent reproductive weakness that will be passed on from generation to generation, thereby challenging future researchers even more.
That being said, there is little doubt that man will continue in his quest to outwit Nature in the reproductive battle. In today's society, that is perhaps as it should be and will result in some stellar equine athletes that otherwise would not have been born.
Causes of Sub-Fertility
Sub-fertility is multi-faceted. If one were to attempt to group or categorize the reasons, they would fall into three general areas: 1) age, 2) contamination and infection of the reproductive tract, and 3) a malfunctioning of the hormonal system. The three will overlap, but for the purposes of this discussion, we'll approach sub-fertility from those viewpoints.
The information that follows comes from a variety of sources, including papers presented at past gatherings of the American Association of Equine Practitioners.
One of the basic reasons mares become sub-fertile is age. Old mares often have a more difficult time conceiving and carrying a foal to term than do young mares. With some aged mares, the problem might involve simple wear and tear on a uterus that has become scarred and compromised to the point that it can no longer adequately house and nourish a growing fetus.
In others, as research at the University of Wisconsin has indicated, the problem might occur before the fertilized egg ever reaches the uterus. The Wisconsin study indicated that ovarian failure was associated with advanced age--mares 20 years and older.
The researchers found that more young mares than old mares had at least three ovulations in a period of approximately 90 days during the natural breeding season from June through September.
Elaine M. Carnevale, DVM, MS, PhD, formerly at the University of Wisconsin and now at Southern Illinois University, who authored a paper summarizing the Wisconsin research, had this to say:
"In mares with at least two sequential ovulations, significant differences included later emergence of the ovulatory wave of follicles, slower growth of the ovulatory follicle, longer interovulatory interval, longer follicular phase, and less luteinizing hormone surge in old than young mares. An atypical appearance of the ovulatory site was imaged with ultrasonography more in old than young mares and might have been associated with luteinized, unruptured follicles or incompletely evacuated follicles. Reproductive senescence in old mares progressed over a number of years as follows: a) elongation of the follicular phase and a reduced number of follicles when compared with other mares, b) occasional ovulations--80 days between ovulations in some cases--and, c) a final state of persistent ovarian inactivity with no follicles larger than five millimeters."
The Wisconsin researchers carried out a second study that was designed to determine whether uterine changes and deterioration in older mares had a negative impact on pregnancy.
Carnevale had this to say:
"In another study, mares 15 years of age and older had significantly more inflammatory and degenerative changes of the uterus and less uterine contractile activity than young mares. These results agreed with previous conclusions that functional and histologic changes occur in the uterus with advanced age. However, to determine the extent that fertility was reduced in old mares prior to the time that the embryo enters the uterus (Day 5 or 6) oviductal embryos from young and old (20 years of age and older) mares were evaluated.
"By Day 1.5, the collection rate of ova (cleaved or uncleaved) and the percentage of cleaved ova were significantly lower in old mares compared to young mares.
"On Day 3, significantly fewer embryos were recovered from old mares, and embryos from old mares had more morphologic abnormalities and retarded growth. Oviductal pregnancy rates on Day 3 were comparable with pregnancy rates of Day 11 for young and old mares, respectively. Results indicated that fertility was reduced in old mares prior to the time that the embryo entered the uterus.
"Oocytes, collected from young and old donors, were transferred into the oviducts of young, artificially inseminated recipients. Significantly fewer oocytes collected from old mares, when compared with young mares, developed to an embryonic vesicle by Day 12. Oocyte viability was reduced in old mares."
The conclusion reached by the Wisconsin researchers was that fertility problems in older mares often occurred earlier in the reproductive cycle than many horse owners had thought.
"Although uterine changes were present in old mares, fertility was reduced prior to the time that the embryo entered the uterus. Therefore, uterine pathology did not appear to be the primary reason for low fertility in old mares. Oocytes were defective and resulted in a significant loss of fertility in old mares. Investigations are needed to determine if defects are intrinsic to oocytes of old mares or if they result from a detrimental follicular milieu and whether oocytes could be salvaged from a harmful environment or treatments could be developed to enhance the viability of follicular oocytes."
Carnevale also was involved in research funded by Purina Mills. The study was aimed at determining whether diet could have an effect on ovulation and pregnancy rates among older mares.
Young mares (three to five years of age) and old mares (19 and older) were used in the study. The mares were primarily of Thoroughbred or Standardbred lineage. They were housed on a 12-acre lot and fed hay. On March 30 of that year, young and old mares were randomly divided into two groups. One group would receive a "nutrient-dense" Purina feed that had been designed specifically for old mares. It would be fed at the rate of 10 pounds per day in addition to alfalfa/orchard grass hay. The second group would receive oats at the rate of 10 pounds per day, plus the same kind and amount of hay.
Reproductive tracts were examined every one to four days via ultrasonography.
The results indicated that the young mares fed the special diet did not differ significantly in ovulation from young mares on the oats-hay diet. However, there were distinct differences in the two groups of older mares.
Carnevale had this to say in her report:
"During the spring, old mares ovulated smaller follicles and had more multiple ovulations than young mares. Old mares fed a highly digestible, nutrient-dense diet ovulated approximately two weeks earlier in the spring than old mares fed an isocaloric control.
"Type of feed did not affect time of ovulation for younger mares. Old mares fed the special diet ovulated on approximately the same mean date as young mares, in contrast to a later ovulation date for old mares fed the control diet. Differences in effects of diet between young and old mares were probably caused by the reduced capabilities of old mares to digest and assimilate feed, resulting in a functional nutrient deficiency. From these data, it is apparent that older horses need to be maintained on a feeding program that supplies them with the additional nutrients that they need for reproductive performance."
Cervical Lacerations and Old Mares
Before leaving the discussion of older mares and the reproductive problems attributed to age, it would be well to note that older mares which have had a foal regularly are more prone to cervical lacerations, even when the delivery is normal.
Of course, a mare of any age can suffer a cervical tear during a difficult birth (dystocia), but age appears to be a definite factor, even when there are no birthing problems.
Corey D. Miller, DVM, of Texas A&M University, conducted a study on the subject, using the medical records of all mares referred to Rood and Riddle Equine Hospital in Kentucky for cervical lacerations between March of 1986 and January of 1995.
His findings were twofold. First, as has been noted, age was a factor in cervical lacerations and, second, surgery to repair the damage often was successful. The post-
surgical pregnancy rate for mares in the study was 75.3%. However, he said, clients should be made aware of the potential for recurrence with subsequent foalings.
Following is Miller's conclusion:
"The results of this study suggest that older (mean age, 12.8 years), multiparous (mean number of foals produced before surgery, 6.2) mares may be predisposed to cervical lacerations. Eighty-six percent of the mares in this study population were presented for surgical laceration repair after an apparently normal parturition. This supports previous anecdotal information that suggested that cervical lacerations are just as likely to occur during an unremarkable parturition as during a dystocia.
"Surgical repair is an effective treatment of cervical lacerations. The potential benefits of the surgery appear to far exceed the few complications associated with the procedure."
The above studies fairly well establish that age is a significant factor in the reproduction process. But, what about the younger mares which don't reproduce? What might be involved with them and even some of the older mares which are ovulating regularly? Infection somewhere along the reproductive tract can be a significant factor.
Each portion of the reproductive tract plays a key role in the mare producing a live foal, from ovaries to fallopian tubes and from vulva to uterus. Any time a part of the reproductive tract becomes contaminated or infected, its ability to function properly could be compromised.
Unfortunately, it is difficult to keep the mare's reproductive system free of contamination. For example, if the vulva is tipped in, fecal matter will fall against it every time the mare defecates. This can result in the reproductive tract becoming contaminated or infected. Or, the labia might lose elasticity and be unable to seal tightly, allowing airborne contaminants to make their way into the reproductive tract.
The way in which the uterus functions when the mare is in heat as opposed to diestrus also can be a factor in contamination. When the mare is not in estrus, the cervix is tightly closed and located in the center of the vaginal wall. When the mare is in heat, the cervix is open and relaxed, actually lying on the vaginal floor. During natural cover breeding, the stallion's penis might penetrate the uterus through the cervix. The same is true of instruments used in artificial insemination. Whatever the approach, the door is open for contaminants.
Contamination of the reproductive tract can result in endometritis, an inflammation of the endometrium, the inner layer of the uterus that is responsible for nourishment of the fetus. Mares which are susceptible to endometritis lack the ability to clear the uterus of bacterial contamination that has been created by breeding.
Mares susceptible to endometritis often will require 96 hours or more to clear the uterus of contaminants, while reproductively normal mares will clear the bacterial contamination within 24 to 48 hours.
"Uterine inflammation that occurs because of breeding must be cleared by 96 hours if the embryo is to survive," says Michelle M. LeBlanc, DVM, Diplomate ACT, of the College of Veterinary Medicine, University of Florida.
"Recent research completed by ourselves and others," she wrote in a paper on the subject, "has shown that a delay in the physical clearance of intrauterine fluids and bacteria through the cervix is a major cause of recurrent endometritis. We have also shown that lymphatic drainage of the uterus is impaired in susceptible mares.
"Lymphatics remove excess fluids that accumulate in tissue spaces and carry proteins and large particulate matter away from tissue spaces, neither of which can be removed by absorption directly into blood capillaries. The reason why susceptible mares exhibit a delay in uterine clearance is not known. Contributing factors include poor perineal conformation, anatomical location of the uterus in relation to the pelvic brim (my preliminary findings), and decreased myometrial contractions after antigenic stimulation."
LeBlanc said that mares having a delay in uterine clearance can be diagnosed by a new scintigraphic procedure performed during estrus or within 48 hours of ovulation. Radiocolloid (radioisotopes in pure form) is infused into the uterus and the amount of colloid cleared in two hours is measured.
Reproductively normal mares, says LeBlanc, clear 50% of the colloids in that time, whereas susceptible mares clear only negligible amounts. The only problem with the method is that the scintigraphy equipment is expensive and is not readily available to the practitioner in the field.
Perhaps a more practical method, says LeBlanc, is an ultrasound examination of bred mares between one and 10 days after ovulation to measure intrauterine fluid.
LeBlanc theorized that treatments designed to improve myometrial contractions or physical clearance could be useful in older mares susceptible to endometritis. Her research goal was to determine the effects of oxytocin on uterine clearance in the laboratory and in clinical cases.
Seven reproductively sound mares and seven mares susceptible to endometritis were used. Mares declared to be reproductively normal were either maiden mares or mares which had produced a number of foals and had no history of infertility.
Clearance of radiocolloid was measured with scintigraphy in all mares on Day 3 of estrus and 48 hours after ovulation. Radiocolloid was infused into the uterus and the initial scintigraphy reading was taken. Then, 20 IUs of oxytocin were given intravenously and clearance of colloid was measured over two hours.
LeBlanc had this to say about the results:
"Oxytocin enhanced the uterine clearance of radiocolloid infused into the uterine lumen in mares resistant and susceptible to endometritis during estrus. Administration of 20 IU of oxytocin intravenously to susceptible and resistant mares resulted in clearance of 90% and more radiocolloid within 15 minutes of intrauterine infusion. The susceptible mares cleared negligible amounts of radiocolloid (about 5%) within four hours when no drug was given.
"Following oxytocin administration, a few mares had sweat on their flanks and shoulders. No other adverse effects were noted."
A second study carried out at the University of Florida involved field trials conducted during the 1993 and 1994 breeding seasons.
Oxytocin was administered in combination with saline uterine lavage to 32 infertile mares. Treatments were performed four to eight hours after breeding and were repeated 24 hours after breeding if all three liters of saline infused into the uterus were cloudy when retrieved.
Oxytocin, also at the 20 IU level, was given intravenously after the uterine lavage was conducted. The mares, ranging in age from four to 24, were stationed at various farms, but all of them had histories of two or more years of recurrent endometritis.
Of the 32 mares involved in the treatment program, reported LeBlanc, 27 (84%) conceived after mating during one estrus.
In her conclusion, LeBlanc had both positive and precautionary remarks about the use of oxytocin:
"Oxytocin dramatically enhanced the clearance of radiocolloid in reproductively normal mares and mares susceptible to endometritis. Oxytocin, in combination with a saline uterine lavage, also improved pregnancy rates in infertile mares exhibiting a delay in uterine clearance. By using the combined treatment, we removed intrauterine fluid containing inflammatory by-products by saline lavage, and uterine contractions are induced with oxytocin. It is not known whether oxytocin by itself will improve pregnancy rates.
"Oxytocin must not be considered a wonder drug because not all mares with endometritis exhibit a delay in uterine clearance. Veterinarians must continue to examine diligently all mares referred for reproductive consultation. Conformational defects have to be noted and corrected surgically if necessary. Examination of the vagina and uterus must be performed as aseptically as possible to reduce iatrogenic infections. Ultrasonographic examination of the reproductive tract should be conducted, if equipment is available, to determine whether fluid is accumulating within the uterine lumen."
Oxytocin and Antibiotic Lavage
A study conducted at the University of Utrecht, The Netherlands, and reported on by J. F. Pycock, BVM, PhD, DESM, MRCVS, added another dimension to using oxytocin--antibiotics were administered as well. Approximately 380 mares--some maiden, some barren, and some which had foals--at seven well-managed public stud farms in the United Kingdom were examined. The ages of the mares ranged from three to 22 years, and the examinations took place during the period of February through September, 1993.
Once in estrus, the mares were placed in one of four treatment groups: 1) no treatment; 2) broad-spectrum, water soluble, intrauterine antibiotic treatment; 3) intravenous injection of 25 IU oxytocin, and 4) an intravenous injection of 25 IU oxytocin followed by intrauterine antibiotic infusion.
Of the 95 mares given only antibiotics, 54 (57%) became pregnant. Of the 95 given oxytocin alone, 62 (65%) became pregnant. Of the 95 given antibiotics and oxytocin, 73 (77%) became pregnant. The lowest pregnancy rate was for the non-treated mares (less than 60%).
"In non-treated mares," reported Pycock, "more fluid accumulated in the uterine lumen after mating, which was the most likely reason for the significantly reduced pregnancy rates."
Following are some of Pycock's conclusions:
"The results of this study have shown the benefits of treatments that either cause the elimination or that reduce the production of intrauterine fluid in the management of post-mating endometritis in the mare. The study avoided the use of an endometritis model and utilized large numbers of mares in normal clinical practice. An important advance was the inclusion of untreated control mares.
"Drainage of fluid following oxytocin injection usually was rapid and visible on ultrasound examination. No untoward clinical signs were observed in any of the mares receiving oxytocin. Pregnancy rates were highest in the mares given intrauterine antibiotics as well as oxytocin. This must suggest two different modes of action of the combination treatment, namely antibacterial activity and fluid drainage, which were additively helpful.
"Antibacterial activity may possibly be linked to the reduction of the intraluminal fluid, because in those mares that were treated with oxytocin alone, some bacteria remained within the uterine lumen, and presumably, the inflammatory effects of these bacteria caused the fluid to accumulate again.
"From the results, it is necessary for one to ask the question, 'Is it desirable to treat every mare routinely after mating regardless of the clinical history?' The answer must be no, because treatment should be restricted to those mares that would benefit. It may be useful to use an ultrasonographic examination of the uterus to identify those mares with uterine fluid after mating and to treat only those mares.
"Another approach that appeared useful was to target categories of mares that benefitted the most from treatment in terms of pregnancy rate. This study indicated two such categories--old mares and mares mated at the first estrus postpartum. This may offer the best approach to prevent unnecessary use of postmating therapy."
Conformational abnormalities often are implicated in reproductive tract infections, some as the result of the aging process and others that are traced to genetics.
We already have mentioned the mare with the tipped-in vulva, seen with some frequency in horses with high, level croups. In cases that result from genetics, one can do nothing to change the mare's basic conformation. This leaves the veterinarian with the option of suturing the upper section of the vulva leaving only an opening for urine to be eliminated--a Caslick's procedure. The purpose is to prevent particulates from entering the reproductive tract from post-mating to foaling time.
The procedure is quite straightforward and simple and is used on many mares where conformation creates the suspicion of contamination.
Not quite so straightforward and simple is the mare which has conformation that allows urine to pool in her reproductive tract, also known as vesicovaginal reflux (VVR) or urovagina. This is a serious problem along the reproductive tract that often is implicated in sub-fertility. In some cases, the only remedy is surgery.
Simply put, urine pooling occurs when urine refluxes in the vagina and against the cervix instead of being flushed to the rear and evacuated through the vulva. The problem is magnified during estrus because of the relaxed state of the cervix, which allows urine to enter the uterus, irritating and contaminating it.
Urine in the forward portion of the reproductive tract, as well as in the uterus itself, produces chemical irritation as well as spermicidal activity. The irritation it causes can provide a breeding ground for harmful bacteria.
Again, age becomes a pre-determining factor. Older mares which have delivered a number of foals are more at risk than younger females, says Gayle Trotter, DVM, a surgeon at Colorado State University who has written textbook literature on the problem and the surgical procedures involved in correcting it.
When the problem does occur in younger mares, says Jack Easley, DVM, MS, of Shelbyville, Ky., also the author of textbook literature on VVR, it could mean urine pooling with added complications. The young mare might have an ectopic ureter--displacement of the tube that conveys urine from the kidney to the bladder--and, as a result, might empty urine into any area along the reproductive tract. This is a problem that can only be solved with surgery.
Under normal circumstances, urine is evacuated from the bladder into the vulvar vestibule and out the open vulvar labia or lips. However, if the normal slope of the vulva is altered approximately 10 degrees from horizontal or the genitourinary tract slopes forward and downward, a splashback of urine can occur, whereby some urine refluxes back toward the cervix and uterus instead of out of the vulva.
The problem is multifaceted. Mares which are wind-suckers, for example, are more apt to be urine poolers. Wind-sucking occurs when the vulvar labia become weakened and do not function properly by providing a tight outer seal for the reproductive tract. When that occurs, air is drawn into the tract, inflating the vaginal vault.
Mares which are wind-suckers (pneumovagina) are prime candidates for urine pooling because when she draws air into her reproductive tract, the vaginal vault is inflated and the entire tract becomes relaxed, eliminating normal barriers.
One of the reasons that barriers along the tract might not be working well, says Trotter, is the bad conformation that has developed, often from multiple births. The loss of muscle tone allows the vagina to tilt forward and one of the barriers, the sphincter, is unable to provide a tight seal in the tract.
There is another side to the coin. Some mares will urine pool only when in estrus. This is the least serious of the urine pooling problems, and the one most easily treated.
Easley explains it this way:
"Depending on the stage of estrus and concentration of estrogen and progesterone, the reproductive tract may be predisposed to urine pooling. Estrogens stimulate and maintain the tissue of the tubular reproductive tract by increasing vascularity and uterine secretions, therefore increasing the area's defense against mechanical insult and infection. A side effect, however, is a mild edema of the tubular tract, vagina, and uterus, resulting from intracellular absorption of water. The pelvic structures and vulva then relax as the general perineal area enlarges and cranial displacement of the reproductive tract follows, leading to urine pooling."
Often, says Trotter, these mares can be managed successfully by manually evacuating the urine, then breeding them. When a pregnancy occurs, the mare's hormonal changes will cause the reproductive tract to return to its normal, firm state and permit the cervix to seal off the uterus.
Because the urine pooling problem might only be a mild one that can be solved without surgery, it is important that the correct diagnosis be made. A surgical procedure on a mare which pools urine only during estrus might do more harm than good.
Trotter, however, adds a note of caution involving mares which only pool urine during estrus:
"Some of these mares become pregnant if the urine is manually evacuated prior to breeding. However, some of these mares also likely suffer early embryonic death of the fetus or accumulate urine more significantly in subsequent years. A full reproductive workup, including a uterine biopsy for prognostic purposes, is recommended prior to embarking on a course of medical or surgical treatment."
For the wind-sucking mare that is also a urine pooler, a Caslick's operation might be the treatment of choice.
When urine pooling persists for whatever reason, however, an internal surgical procedure could be the only solution.
To this point, we have discussed some ways to prevent endometritis, plus some of the basic culprits along the way. When endometritis does strike, it must be dealt with immediately by the practitioner in the field if the mare is to be a viable producer.
"It has always been amazing to me," says Jim Briddle, DVM, a Kansas State University graduate and practitioner near Riverton, Wyo., "that we don't get more uterine infections post-coitus. After all, the mare's cervix relaxes completely, and when the stallion breeds her, his penis goes through the cervix and all the way into the uterus. Thus, there is great potential for bacteria to be deposited in the uterus."
Listed by many veterinarians and research-ers as the most common bacteria involved in endometritis is Streptococcus zooepidemicus. Two other prime culprits are Pseudomonas aeruginosa and Klebsiella pneumoniae.
The good news at this stage is that while a multitude of bacteria enters the uterus during the breeding procedure, this is also the time when the mare's immune system is functioning at its peak. Thus, most healthy mares are able to fight off the bacteria. However, as already indicated, a number of mares are unable to do this and must be treated.
In order for the practitioner to know what he or she is dealing with specifically, a culture is necessary, says Briddle. Only when the veterinarian knows exactly what bacterial organism is involved can the correct decision be made as to which antibiotic is appropriate.
"A practitioner can do a lot with a microscope right there at the clinic," Briddle says. "If there are bacteria present, you are going to be able to see them and you may be able to determine what general type is involved."
By studying a uterine culture in the clinic, Briddle feels the practitioner can get a head start on treatment while awaiting official results from a laboratory. One of the most beneficial services the laboratory provides, he says, is to isolate the bacteria and recommend an antibiotic that sensitivity tests have demonstrated has the capability of destroying it.
One of the procedures the practitioner can perform while awaiting laboratory results is cleansing the uterus via uterine lavage with one to two liters of sterile saline, plus, as mentioned above, administration of oxytocin.
Repeated bouts with endometritis can result in uterine cysts, says Scott Bennett, DVM, of Equine Services, a clinic and equine hospital in Simpsonville, Ky., that is heavily involved in the reproductive field. The cysts will develop in an older mare after multiple births. They are rare in young mares unless those mares have had ongoing bouts with endometritis.
The cyst problem crops up in the wake of scar tissue that develops within the uterus as the result of infection or multiple births. What happens then is a clogging of the lymphatic draining system by the scar tissue. The result is a cyst or cysts filled with fluid that normally would be evacuated.
"A few cysts within the uterus won't make that much difference, unless they are large," says Bennett. "Their ability to compromise the function of the uterus is dependent on their size and number. Normally, I don't worry about two or three small cysts, but one big cyst can become a major problem.
"In some mares, there will be 10 or 12 cysts, and their presence in that number will definitely cause problems even though they may not be large. The cysts become physically obstructive, sometimes preventing semen from entering the uterus and, if a pregnancy does occur, can compromise mobility of the embryo. That is how the embryo gives the signal that a pregnancy has occurred, by wandering through the uterus for the first 18 days."
When cysts are suspected, it is time for a thorough uterine examination, says Bennett.
Following are some of the tools and approaches modern technology has made available to the practitioner to conduct a complete uterine exam.
Endometrial culture--An endometrial culture is a general evaluation of the bacterial status of the uterine lumen. "It must be remembered," says Bennett, "that a negative culture simply means that you did not culture any bacterial growth from that swab. Conversely, a positive culture does not necessarily mean that the uterus has a pathological condition and is subject to interpretation."
Cytology--This involves studying slide samples under the microscope.
Endometrial biopsy--"By far, one of the most beneficial methods of evaluating the endometrial integrity is with the endometrial biopsy," says Bennett. ‘The uterus of problem broodmares can vary widely within the uterus itself. Through hysteroscopy, we have diagnosed focal changes within the uterus that may be missed with a 'blind' biopsy technique."
Hysteroscopy--Hysteroscopy involves using a flexible fiberoptiscope to visualize the structures within the uterus. Bennett explains the utilization of hysteroscopy this way: "The mare's rectum is evacuated and the vulva and perineal area prepared aseptically. Insufflation of the uterine lumen may be done with filtered air, carbon dioxide, or fluid. Filtered air or carbon dioxide is my preference, as fluid often will cloud with suppurative endometritis, making the exam more complicated. Early estrus or post-estrus is preferable because insufflation is difficult when the cervix is open during estrus. The structures that can be examined include the cervix, endometrium, uterine bifurcation, and tubal uterine junctions. Abnormalities that can easily be seen include infection, cysts, scar tissue, adhesions, and tubal-uterine junction pathology."
Ultrasound--Ultrasound is a valuable tool, not only for demonstrating pregnancy, but also for evaluating uterine pathology. Endometrial cysts, fibrous masses, fluid, uterine tumors, ovarian tumors, ovarian hematomas, and ovarian cysts often can be differentiated using ultrasound.
Laparoscopy--This involves a surgical procedure, most often performed through the flank, in an effort to view parts of the reproductive tract. The procedure has been rendered nearly obsolete by the advent of ultrasonography. One important use remaining for the procedure, Bennett believes, is in "demonstrating fimbrial disease and obvious oviduct disease."
Tubal patency--Bennett believes that a tubal blockage cannot be diagnosed through palpation, ultrasound, or laproscopic examination unless a grossly obvious condition exists. The tubal patency procedure, simply put, involves flushing a dye through the oviduct and, by observing what occurs with it, determining where the problem lies.
Another tool that technology has provided and which is highly important in such uterine surgeries as removal of cysts is the surgical laser.
"The laser has been absolutely a godsend," says Bennett. "A lot of the uterine cysts are high up in the horn and you have to literally go around a corner to get to them. That is difficult to do with a traditional straight instrument."
The surgical procedure is rendered even more simple when the laser is harbored within an endoscope that is inserted into the uterus via the vagina. This approach allows the practitioner to visualize the interior of the uterus, locate the cysts, and vaporize them.
A quick review of what happens when a mare's hormonal system awakes and prepares her body for pregnancy is in order. As the mare's brain records increased light and higher temperatures with the advent of spring and summer, the hypothalamus gland, located within tissues of the mid-brain, is stimulated. It signals the start of the reproductive system by producing a gonadotropic releasing hormone (GnRH). When GnRH is secreted in the proper quantity, the pituitary gland, located at the base of the brain, is stimulated. The pituitary then secretes two hormones that affect the ovaries. The first hormone is known as follicle stimulating hormone (FSH). It travels along the bloodstream to the ovaries where it stimulates development of one or more follicles.
The follicles, when they reach 20 to 25 millimeters in diameter, secrete estrogen. This hormone stimulates estrual activity, causes relaxation of the cervix, stimulates contractions along the mare's reproductive tract, and signals the pituitary gland to cease secretion of FSH and, at the same time, stimulates release of the second gonadotropic hormone--luteinizing hormone (LH).
The luteinizing hormone facilitates maturation and ovulation of the growing, egg-bearing follicle.
Ovulation occurs when the mature egg leaves the follicle and begins its trip through the oviduct. In the wake of ovulation, the estrogen level falls and the remains of the ovulated follicle are converted to form a corpus luteum (CL) or yellow body. The luteal cells secrete the hormone progesterone. It is the job of progesterone to shut down the estrus-stimulating hormones and to set the stage for maintaining a pregnancy.
Its initial task is to subdue the actively contracting reproductive tract and to tighten and close the relaxed and open cervix. It also prohibits the secretion of FSH and LH from the pituitary, thus effectively putting the mare out of heat.
As can easily be seen, progesterone is a highly important hormone in maintaining a pregnancy. In some sub-fertile mares, the correct amount of progesterone is not secreted and, when that is the case, the other hormones swing into action to terminate the pregnancy and bring the mare back into heat.
Fortunately, progesterone levels can be monitored and supplemental progesterone can be administered to the mare throughout the pregnancy.
Proper timing of secretion and appropriate levels of all hormones are required to maintain a reproductive balance during breeding and pregnancy. When there is an imbalance anywhere along the way, fertility problems will follow. Mares that are subfertile because of an imbalance must be monitored and dealt with by a veterinarian.
Lighting the Cycle
As can be seen in the foregoing, there are a great many problems that can beset a mare and cause her to become sub-fertile. When dealing with a sub-fertile mare, time can become an enemy that practitioners and owners must turn into an ally. This means bringing the mare into heat early in the year to provide a greater window of opportunity to deal with the problems that are causing her to be sub-fertile.
Bennett recommends that mares be put under lights beginning about Nov. 15 as part of the effort to get an early start on the breeding season. A 200-watt bulb that is placed over a 12 X 12-foot box stall for 16 hours a day is best, he says.
Stress also should be minimized for the sub-fertile mare, and other broodmares as well. Some mares on the low end of the pecking order in a group, for example, would do better quartered alone or with other mares which do not pose threats.
The good broodmare manager will take a year-around approach to the sub-fertility problem, combining sound management with veterinary help.
Even then, we must remember, there are some mares whose reproductive systems simply shut down as the result of age and multiple births, and there is little we can do about it. And there are others that Nature has decreed, through genetics and conformation, that are not meant to bear young.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.