Chapter 24 BREEDING THE POST-PARTUM MARE
It has been shown that in order to keep a 12-month inter-foaling interval, the average number of days from foaling to conception must be around 25 days. Therefore, mares must be bred at the earliest opportunity that will give them the best chance for conceiving and maintaining the pregnancy.
In order to determine this optimal time, it is important to know the physiology of the post-partum mare. On average, mares start their first post-partum heat around 6 or 7 days and ovulate on days 9–11. Therefore, mares that have foaled normally have been normal since foaling and are to be bred on foal heat should be examined by day 6, 7, or 8 post-partum. This allows for several goals to be achieved during this examination. The mare’s reproductive health can be ascertained, where she is in her cycle can be determined, and plans can be made to obtain semen or book her to a stallion in time to be bred prior to ovulation. (The growth size of her ovulatory follicle will determine if sequential examinations are necessary prior to breeding this cycle.) This first foal heat examination should consist of a thorough visual examination of the external genitalia, vestibule, vagina, and cervix, as well as an assessment of the uterus, broad ligament, and ovaries by transrectal palpation and ultrasonography.
Mares that appear to have no foaling complications are still examined for tears and bruising of the vulva and vestibule as well as lacerations to the vagina and cervix. The more difficult the birth, the more likely these traumas are to occur; however, they can occur in any foaling mare and with an increased frequency in primiparous mares. Therefore, a careful vaginal speculum examination is necessary; if there is any doubt of cervical trauma on the part of the veterinarian, he or she should perform a digital examination on the cervix to determine the extent of the damage. Not only unexpected trauma may be discovered during this examination, but a not-yet-detected uterine discharge may be discovered during this foal heat examination. As mentioned, careful palpation and ultrasonographic evaluation is also necessary at this time to not only assess estral status, but to ascertain signs of internal trauma such as hematomas caused by uterine artery ruptures and bleeding in to the broad ligament.
However, this initial examination should take place prior to foal heat if the foaling was abnormal, the placenta was retained or was grossly abnormal, or the mare develops an abnormal uterine discharge. Obviously an abnormal birth or placenta will be realized at or soon after parturition, but a uterine discharge may not develop for several days. Therefore, it is incumbent upon the breeder to be looking for signs of discharge that sometimes can be obvious visually. However, there are those that are not, and monitoring the temperature daily on these post-partum mares can be valuable in detecting a uterine discharge in that most will develop a fever of varying degrees. Mares that are unable to go outside and exercise in the days after foaling will have a greater chance of developing a uterine discharge. When inclement weather or problems with the foal dictate that the mare stay in the barn, she is unable to exercise normally and is less likely to get up and down and roll as she would outside. These normal activities are part of the physical process of uterine clearance in the post-foaling uterus as it involutes. Administration of oxytocin may help avoid a uterine discharge by aiding with uterine clearance.
Assessing the foal heat begins at day 6, 7, or 8, depending on how much notice is needed in getting on the stallion’s breeding book or ordering cooled semen. As mentioned previously, the examination should consist of the visual assessment of the perineum, the speculum examination, and the transrectal palpation and ultrasound examination. As with any pre-breeding examination, the cervical relaxation, uterine edema, and follicle size are all monitored and their progression is used to predict ovulation or to time the administration of an ovulatory agent.
Foal heat is somewhat different from subsequent heats in this process because of the possibility of post-foaling trauma or uterine discharge. Prudently, evidence of trauma of any severity would mean not breeding this heat and giving the mare time to heal and recover from such. Uterine discharge would also mean “passing” this heat, but would also indicate treatment by uterine lavage, ecbolics, and possibly systemic antibiotics and anti-inflammatories in severe cases.
During the transrectal ultrasound examination of the foal heat mare, there is a slightly increased propensity to find more uterine fluid than in subsequent cycles. The fluid is often of a normal character (anechoic) but of more volume than expected. These mares may be candidates for “passing” as well, especially if the fluid does not resolve with administration of an ecbolic.