Most causes of dystocia in the mare are due to abnormal presentation, position, or posture. A dead or compromised fetus often is not properly positioned in the pelvic canal. Fetal–maternal disproportion and primary uterine inertia are rare in the mare. A vaginal examination should be performed if the foal is not delivered within 30 min after rupture of the chorioallantois or if second-stage labor fails to progress after >4 hr of obvious first-stage labor.
The initial examination may be performed in the standing mare. The perineum should be cleansed with povidone-iodine scrub and rinsed well with water. Efforts should be made to maintain hygiene at all times. A diagnosis of the presentation, position, and posture must be made, and a plan formulated to manipulate the fetus into anterior longitudinal, dorsosacral position with head, neck, and front limbs extended. Copious amounts of clean lubricant will ease manipulations and fetal expulsion. Excessive mechanical or manual traction should be avoided. Length of time spent on manipulations and progress should be noted. If the fetus cannot be delivered using traction exerted by two strong adults, the diagnosis should be reconsidered and plan of action altered.
Sedation can be provided by the administration of xylazine (0.5–1.0 mg/kg, IV) and butorphanol (0.01–0.02 mg/kg, IV). If abdominal straining prevents adequate vaginal examination and fetal mutation, epidural anesthesia may be administered using xylazine (0.17 mg/kg) and lidocaine (0.22 mg/kg) diluted to a total volume of 8 mL.
The fetus' front legs should be identified and extended out the vulva. Obstetrical chains applied to the distal metacarpals will aid manipulation and assist the application of traction. Once the head is exposed and the neck extended, it may be possible to intubate the fetus and administer low flow oxygen using a portable oxygen tank or ventilate with a resuscitator (ambu bag). Proper rotation of the fetus may be facilitated by the mare getting up and down. After confirming that the fetus is in the proper orientation, manual traction can be applied, initially dorsally and then caudally. Once the foal's chest is exposed, traction should be applied in a ventral caudal direction. Traction should be applied intermittently in rhythm with the mare's abdominal contractions.
After the foal is delivered, an internal examination should be performed to identify any lacerations in the mare's genital tract or the presence of a twin. A few low doses of oxytocin (5–10 IU, IV or IM) can be administered every 15–20 min to stimulate passage of the fetal membranes and uterine evacuation. Repair of primary perineal lacerations usually can be delayed until after foal heat, but the dorsal aspect of the vulvar lips should be temporarily sutured if pneumovagina/pneumometra develops.
Controlled Vaginal Delivery
A controlled vaginal delivery may be made in an anesthetized mare. The mare's hindquarters are hoisted to allow the GI tract to move cranially in the abdomen, providing space to more readily perform fetal manipulations. If general anesthesia and a controlled vaginal delivery are likely, epidural anesthesia should not be done. Field anesthesia can be accomplished by first heavily sedating with xylazine (1.0 mg/kg, IV) followed by diazepam (0.05–0.1 mg/kg, IV) and ketamine (2.2–2.5 mg/kg, IV). If gas anesthesia is available, routine induction and maintenance by inhalation will provide longer working time and greater relaxation.
If vaginal delivery attempts fail, the mare's value justifies it, and surgical facilities are available, a decision should rapidly be made to deliver the foal by cesarean section to spare the caudal genital tract further trauma. Treatment for retained placenta should be initiated immediately after surgery. Barring complications, mares can usually be rebred 60 days after cesarean section.
If surgical facilities are not available or the economic situation prevents referral to a surgical facility, a fetotomy may allow delivery of the fetus. Usually, fetotomy is recommended only if fetal expulsion can be accomplished after 1 or 2 cuts. Care should be taken to avoid damage to the mare's cervix and pelvic canal. Treatment for retained placenta should be initiated immediately after fetal delivery.
Last full review/revision July 2011 by Patricia L. Sertich, MS, VMD, DACT