Maximizing the use of ultrasonography in reproduction (Proceedings)

The mare under the influence of estrogen will have an increase of edema of the reproductive tract. This includes mild hyperemia of the vulvar lips and vagina with a concomitant relaxation of the vaginal vault and cervix. The mare has an average of 5-10 endometrial folds that when under the influence of estrogen become markedly edematous. A mare in standing heat will display a characteristic pattern of edema that could be described as a cart wheel pattern. As the endometrial folds become hyopechogenic in the center and hyperechogenic in the borders. Just prior to ovulation and during the diestrus period the reproductive tract will starts a progesterone dominance and the endometrial edema is no longer present under normal circumstances. The appearance and disappearance of endometrial edema are related with the onset of estrus and ovulation in mares and is a progressive phenomenon that has a typical pattern during the estrus period. The present paper describes a scoring system for endometrial edema (SEE) detected by transrectal ultrasonography, and the use of the pattern of endometrial edema as a tool to help veterinarians: a) improve the prediction of the time of ovulation in normal mares, b) detect mares that need post-breeding therapies such as uterine lavage, oxytocin or caslicks operation.

A subjective scoring system (0-5) for the degree of endometrial edema (score of endometrial edema SEE) was established. A grade of zero (0) was given to mares that were in diestrus and had no uterine edema and a grade of five (5) was assigned to mares with maximal uterine edema. In order to use this scoring system the mares were examined on a regular basis throughout their estrus cycle and the pattern of endometrial edema determined. Teasing was done on a daily basis in the thoroughbred population and behavioral signs correlated with appearance of uterine edema. In addition SEE, follicle size and time of ovulation were recorded after injection of 2500 IU of HCG or Ovuplant treatment.

In the normal mare, there is a typical pattern of appearance and disappearance of the uterine edema that can be followed ultrasonographically. Mares will start displaying signs of behavioral heat when the ultrasound score reaches around two. (X= 1.83 range 1-4) From there on, the score will increase gradually until it reaches its maximal degree (X= 4.3 range 3-5). It is at this point when mares will respond most consistently to hCG with follicular size very often larger than 35 mm. Of the mares that I have treated with hCG 98% have ovulated within 48 hrs. Follicle size in these mares has been an average of 39.8 mm ranging between 33 and 49 mm. From the time that mares reach their peak SEE or are treated with HCG, endometrial edema starts to gradually decrease as the mare approaches ovulation. The normal mare will ovulate within a few hours after the SEE has decreased to an average of 1.3 range between 1-4. In most mares impending ovulation will coincide with a history of behavioral estrus for four or five days and a preovulatory size follicle 40-55 mm in size. The ultrasonographic appearance of the follicle that is approaching ovulation is quite distinct with irregular borders, and hyperechogenic walls. This follicle in general is painful and will be soft at palpation depending on its location within the ovary.

Frequently veterinarians working at breeding farms do not have the opportunity to follow a mare during the entire estrous cycle and often the mares are already in standing heat when they are presented.

Mares in estrus

Frequently a mare is presented for breeding when she is in standing heat. Veterinarians often are puzzled on when to breed these mares particularly when they should be bred to a heavily booked stallion. The degree of uterine edema combined with follicular size is an important marker to decide when these mares should be bred. Low SUE (1-2) and the presence of a large follicle often > than 40 mm, is a good indication of imminent ovulation. On the other hand low SEE with follicles less than 38 mm would be suggestive of a mare in early estrus. Furthermore the presence of uterine edema is the most reliable indicator of heat in the normal mare even when they do not respond to teasing or a teaser is not available.

Transitional mares

Mares early in the breeding season might display behavioral signs of heat. These heats in general can be quite erratic and unpredictable and very often are anovulatory heats. The presence of uterine edema in these mares unlike the cycling mare does not follow the pattern described above. However, the detection of edema is indicative of estrogenic competence of the follicles. Mares with distinct uterine edema and follicles less than 35 mm could be started on progesterone or progestagen therapy. Mares with uterine edema and a follicle grater than 35 mm, can be treated with an ovulation inducing agent.

Mares in diestrous

Mares presented to a breeding farm are often in diestrous. These mares are often given prostaglandin to induce their heat. The appearance of endometrial edema in these mares will depend on the size of the follicle present at the time of treatment. Mares with follicles over 30 mm will display uterine edema sooner than those mares having smaller follicles.

Abnormalities of the endometrial edema pattern

As stated above a normal mare will have a marked decrease in endometrial edema (SEE) as she approaches ovulation. However there are some instances when mares ovulate with a high degree of endometrial edema (SEE 4-5). In my experience these mares very often have either poor perineal conformation predisposing them to aspirate air and/or have clinical or subclinical endometritis. Very often these mares benefit from post-breeding therapies such as uterine lavage and/or antibiotic infusions. Mares that are bred and ovulate with no marked decrease in SEE often will have marked accumulations of uterine fluid.

Mares with endometrial edema prior to their expected return to a normal heat should be considered as having a short luteal phase that would suggest the possibility of a uterine infection. Furthermore mares that are pregnant with a high degree of wide spread uterine edema often undergo early embryonic death in the first 30 days of gestation. The presence of ultrasonographically detectable uterine edema 15 or 16 days after their last ovulation should alert the veterinarian of a potential problem.

Timing of ovulation of mares at breeding farms is imperative to maximizing pregnancy rates. This becomes even more important with heavily booked stallions or when artificial insemination with transported or frozen semen is used. Detection of the pattern of uterine edema with ultrasonography, combined with rectal palpation of the follicles and the use of ovulation inducing agents helps veterinarians determine the optimal time for breeding of a normal mare. In addition the routine examination of mares will help veterinarians: 1) Determine the optimal time for the administration of ovulatory agents such as hCG or Ovuplant; 2). Determine mares that are in true standing estrus when a teasing stallion is not available; 3) Determine when there is estrogenic competence of follicles in transitional mares; 4) Diagnose uterine inflammation that might indicate uterine infection, urine pooling and/or pneumouterus and implement appropriate therapy; 5) Make a prognosis of the possibility of early embryonic death.

There is a great deal of controversy regarding the timing of injection of ovulatory agents. Treatment with hCG has been demonstrated to induce ovulation 36-48 after treatment when administered to mares that have a >35 mm follicle. However there are a certain percentage of mares that will not respond, probably due to "immature follicles" or the fact that these mares are not in estrus even though a large follicle has been detected.

In my experience using the SEE has proven to be the most helpful aid to determine the appropriate time for giving hCG and determining ovulation in mares. However, the routine examination of the mares at regular intervals is imperative to be able to implement this system. I treat mares with hCG when the SEE has reached a score of four or five. Which means some mares will have a 35mm follicle while in others the follicle might be 40 mm or larger. Using this system the response to this agents is over 95% in the first two cycles. The decrease in the pattern of uterine edema is accelerated by the use of ovulatory inducing agents as the mare approaches ovulation. Although the pattern of appearance and disappearance on uterine edema is fairly consistent in the barren and young maiden mare, I have found its usefulness quite limited in postpartum mares with less than 20 days post-foaling.

In conclusion this system has worked for me and I have been able to significantly reduce the number of breedings per mare. Furthermore I have been able to predict with more accuracy what mares should have a uterine culture, treated post breeding or are more likely to undergo early embryonic death. Abnormalities in the appearance and disappearance of uterine edema, will help veterinarians predict which mares should have a uterine culture in addition to those that and those that might need post breeding therapies.

References

1. Ginther OJ. (1995) Uterus In: Ultrasonic Imaging and Animal Reproduction: Horses pp. 97-99

2. Griffin PG and Ginther OJ (1991) Dynamics of uterine diameter and endometrial morphology during the estrous cycle and early pregnancy in mares. Anim. Reprod. Sci. 25:133.

3. Hayes KEN, Pierson RA, Scraba ST and Ginther OJ (1985) Effects of Estrous cycle season and ultrasonic uterine anatomy in mares. Theriogenology 24:465.

4. Samper JC, (1997) Ultrasonographic appearance and the pattern of uterine edema to time ovulation in mares. Procc. Am. Ass. Equine Pract. Phoenix pp.189-191

5. Pelehach LM, Greaves HE, Porter MB, Desvousges A Sharp DC. (2002) The role of estrogen and progesterone in the induction and dissipation of uterine edema in mares. Theriogenology 58:441-444

6. Voss JL, Pickett BW, Burwash LD and Daniels WH (1974) Effect of Human Chorionic Gonadotrophin on duration of estrous cycle and fertility of normally cycling non-lactating mares. JAVMA 165: 704.