Three natural barriers protect the uterus from bacterial contamination. The cervix, vulvar lips, and vestibular sphincter are all susceptible to trauma during foaling, and especially during obstetrical manipulations. Serious life-threatening complications, however, seldom result from these injuries.
Although cervical lacerations are most commonly associated with dystocia, they can occur during unassisted deliveries. The most common cause is a large fetus. Overzealous foaling attendants can increase the prevalence of cervical tears on a farm by applying traction to the fetal limbs before the cervix has fully dilated. Any assisted delivery should heighten awareness of the possibility of a cervical injury. Diagnosis at the time of fetal extraction is difficult because the cervix is edematous and widely dilated. Dilation of the cervical musculature results in a thin, flaccid cervix that is not readily identifiable on speculum or digital examination during the immediate postpartum period. Inability to confirm the presence of cervical tears at the time of injury is not an impediment since surgical repair should not be attempted until complete uterine involution has occurred. The acutely damaged cervical tissue will be edematous and friable. The recently gravid uterus will be heavy, and difficult to retract caudally to permit surgical accessibility. Some healing of the lacerated cervix will occur spontaneously and no medical therapy other than routine postpartum care is required.
Confirmation of a cervical tear is made during a reproductive exam approximately 30 days postfoaling. Manual examination of the cervix is required because the outline of the cervical os during speculum examination may appear normal if the mucosa is intact. This is frequently the case. Digital examination is accomplished by a combination of the thumb and index finger. Typically the clinician inserts the index finger into the cervical canal and palpates the thumb against it circumferentially around the cervix. The goal is to detect any defect of the cervical musculature as evidenced by thinning of the cervical wall. The optimal time to perform this examination is during diestrus. Progesterone supplementation can be used for 2 to 3 days before the examination to ensure maximal cervical closure. The external cervical os should provide an initial level of resistance to the forward progression of the index finger. The location of lacerations is usually reported in reference to the face of a clock, and the length is reported in centimeters. The length of the defect must be estimated because some tears may not warrant repair. Defects that involve only a small percentage of the length of the cervical canal may still provide a functional barrier to the gravid uterus. Cervical defects that involve less than 25% of the length of the cervix probably do not require surgical intervention. Defects involving between 25% to 50% of the length of the cervix may benefit from repair. Defects of 50% or greater do require repair if the mare is to have a chance of carrying a foal to term. Obviously surgical repair is only indicated if the mare is to be used for breeding. The prognosis for future fertility following surgical repair of a lacerated cervix is reported to be approximately 60%. Owners should be advised that the cervix is unlikely to dilate normally after surgical repair, and that it is likely to tear again. Close monitoring of mammary secretions (electrolyte changes) can be used to select the most optimum time for an elective cesarean section.