Criteria for Selection of Cases

Records from the Faculty of Veterinary Medicine, University of Teramo and the Veterinary Clinical Department, University of Bologna were searched. Records for 72 mares with dystocia and in which the fetuses were nonviable were reviewed. All mares were those in which a fetotomy had been performed at stud farms from 1991 through 2005. During this period, viable foals in mares with dystocia were born via assisted vaginal delivery or cesarean section (those data were not analyzed). Theriogenologists on the veterinary school staff performed dystocia examinations and fetotomies at the stud farms.

Procedures

Data collection—Information pertaining to breed, age, and parity was recorded. Fetal presentation, position, and posture were determined by transrectal palpation, and the information was recorded. The time from chorioallantoic membrane rupture to arrival of a veterinarian at the stud farm was estimated from the history provided by farm personnel at the time clinical examination was performed.

Fetotomy—For examination of dystocia, the tail of each mare was tied to 1 side and the perineal area carefully cleansed. The examiner, wearing a sterile glove and with proper lubrication, determined whether there were lacerations in the birth canal, appropriate cervical relaxation, and uterine muscular spasm. The birth canal was lubricated with polyethylene polymer powder^a and clean water, which were instilled into the uterine lumen by means of a sterile stomach tube and pump. Assisted vaginal delivery and manual resolution of dystocia were attempted, but manipulations were kept to a minimum, and repeated in-and-out arm movements were avoided.

Fetotomy was performed on each nonviable fetus with the mare sedated and standing in a stall bedded with clean straw. Detomidine chloridrate (0.8 mg/kg [0.36 mg/lb], IV) and butorphanol (0.01 to 0.02 mg/kg [0.005 to 0.01 mg/lb], IV) were used for sedation, and 5 to 7 mL of 2% lidocaine was used for epidural anesthesia. Equipment used to perform fetotomy consisted of a Thygesen fetotome (85 cm), Liess wire saw, wire-saw sounding line, curved introducer, wire-saw threader, and 2-armed Krey-Schöttler obstetric hook; an obstetric snare and chain; and eyehooks, handgrips for the wire saw, and sterile rubber sleeves. After introducing the fetotome into the birth canal, the clinician passed the wire saw over the fetal body part to be amputated and held the head of the instrument securely against the relevant part of the fetus. An assistant applied handgrips to the wire saw and commenced cutting with slow, short toand-fro arm movements. To keep the amount of heat generated to a minimum, length of the arm movements and pressure applied on the wire saw were increased only after the wire was properly seated.

Mares were monitored via follow-up examinations for 7 days after fetotomy. Mares with retained fetal membranes (ie, fetal membranes were not expelled within 3 to 6 hours after fetotomy) were treated with oxytocin (20 units, IV) every 1 to 2 hours until the fetal membranes were expelled. Owners were advised that mares should not be bred for at least 2 months after fetotomy.

For the purposes of the study reported here, short-term fertility was considered to be the pregnancy rate at 45 days after breeding. Pregnancy was determined by use of transrectal ultrasonography and visual confirmation of a fetal heartbeat. To evaluate the effect of fetotomy on resumption of reproductive activity, the percentage of mares pregnant 45 days after breeding was compared with that in 124 control mares that were bred after a normal parturition.

Statistical analysis—Comparison between short-term fertility in mares in which a fetotomy was performed and control mares was made by use of commercial software.^b Values of P ≤ 0.05 were considered significant.

Results

Records for 72 mares examined for severe dystocia were included in the study. Breeds represented were Standardbred (n = 38 mares), Thoroughbred (27), Breton (5), and Andalusian (2). Mares were from 5 to 13 years of age, and all were multiparous. All fetuses were nonviable, likely because of the time between detection of dystocia and arrival of a veterinarian (range, 6 to 18 hours).

During initial examination, mares had signs of severe dystocia resulting from loss of fetal viability and abnormalities in fetal presentation, position, or posture. Fifty-four (75%) fetuses were in anterior presentation, 13 (18.1%) were in posterior presentation, and 5 (6.9%) were in transverse presentation. The most common type of fetal malposture for foals in anterior presentation was deviation of the head and neck (n = 31 [57.4%] foals in anterior presentation). Of those 31 fetuses, the head and neck were deviated laterally in 21 (67.7%) and ventrally in 10 (32.3%). Other types of fetal malposture included carpal flexion (n = 11 foals) and shoulder joint flexion (6). Carpal flexion was more often bilateral (n = 10 foals) than unilateral (1), and the frequency of unilateral shoulder joint flexion (3) was the same as that of bilateral shoulder joint flexion (3). Other causes of dystocia in fetuses in anterior presentation included foot-nape posture (n = 2 [3.7%] foals) and 1 (1.8%) each for incomplete extension of the elbow joint, dog-sitting posture, fetal macrosomia associated with trauma to the birth canal, and hydrocephalus. Malposture associated with posterior presentation included tibiotarsal joint flexion (n = 8 foals) and hip joint flexion (5).

Fetotomy had been performed in all mares because examination revealed that the fetus was nonviable, there were financial considerations, or both. Partial fetotomy was performed in 71 of 72 (98.6%) mares with dystocia, and dystocia was resolved with 2 cuts in 67 of 71 (94.4%) mares and with 3 cuts in the other 4 (5.6%) mares. The remaining fetus required 5 cuts to enable removal. That fetus was in anterior presentation and had an enlarged dorsum and hind limbs; cuts were made through the carpal joint of both forelimbs and the neck, thorax, and pelvis.

Mean ± SD time between arrival of a veterinarian and fetal extraction was 12.8 ± 6.8 minutes (range, 5 to 42 minutes). Information pertaining to examinations conducted by other personnel prior to arrival was not reported. The time between rupture of the chorioallantois and arrival of a veterinarian (range, approx 6 to 18 hours) was determined on the basis of information provided by stud farm personnel. Complications after fetotomy included retained fetal membranes (n = 4 [5.5%] mares), laminitis (5 [6.9%]), vaginal and cervical lacerations (2 [2.8%]), and delayed uterine involution (2 [2.8%]). No instances of metritis, peritonitis, or radial or facial nerve paralysis were recorded. The fatality rate was 4.2% (3 mares). One of those 3 mares (1.4% of all mares in the study) had rupture of the uterine wall after a fall and died from subsequent hemorrhage. The other 2 mares that died had signs of severe endotoxemia after prolonged dystocia and fetal maceration.

Sixty-eight of 69 mares that survived were bred 2 to 3 months after fetotomy; 55 became pregnant (pregnancy rate, 79.4%). One mare was euthanized because it fractured a hind limb approximately 2 months after dystocia. Of 124 control mares, 102 (82.3%) became pregnant. The difference in pregnancy rate between mares in which a fetotomy was performed and control mares was not significant (P = 0.419; χ² = 0.654).

Discussion

Dystocia in mares is considered to be a true emergency, and the duration of attempts to deliver a foal substantially influences the survival rate of affected foals.¹⁴ In 1 study²¹ of mares, 99% of the foals were in anterior presentation, 1% were in posterior presentation, and 0.1% were in transverse presentation. In another study¹² of 601 mares with dystocia, 67.9% had a foal in anterior presentation, 15.8% had a foal in posterior presentation, and 16.3% had a foal in transverse presentation. Other investigators² found that 76% of 141 mares with dystocia had a fetus in anterior presentation, 14% had a fetus in posterior presentation, and 10% had a fetus in transverse presentation. These findings were in agreement with results of the study reported here in which 75% of the fetuses were in anterior presentation, 18.1% were in posterior presentation, and 6.9% were in transverse presentation. However, our findings cannot be extrapolated to other populations of mares because the mares we evaluated had severe and lengthy dystocia and the prevalences of the various fetal presentations may not be representative of other populations of mares with dystocia. In contrast to findings in another study² that involved fetal position, we found that the dorsosacral position was the most common in fetuses in anterior and posterior presentation.

The nonviable fetuses in the mares of the study reported here had probably died because of the lengthy period of dystocia (6 to 18 hours). In 1 study,²² 42% of foals were alive when delivered after a mean of 1.8 hours of dystocia, whereas another study⁸ revealed that only 11% of foals were alive at delivery when dystocia lasted 5 to 6 hours. A nonviable fetus is regarded as an indication for fetotomy, provided the clinician is experienced in the technique.^12,19 In 1 study,¹⁶ partial fetotomy was the method of choice for resolution in > 80% of mares in which reduction of dystocia was not amenable to manual correction. Fetotomy can correct dystocia quickly by decreasing the size of a fetus and enabling safe extraction. In the study reported here, mean time required for assessment, induction of local anesthesia, and fetotomy was 12.8 minutes. Injuries caused by prolonged manipulation associated with assisted vaginal delivery that can injure tissues of the birth canal and reduce fertility were thus avoided.¹⁸ Furthermore, fetotomy can spare owners the expense and risk involved with cesarean section.^12,19 Survival rates of 80%¹⁰ to 85%⁸ have been reported in mares undergoing elective cesarean section. In our study, the mortality rate was 4.2%, which is less than the 15% reported for elective cesarean section in another study.⁸ This finding was surprising given the lengthy period of dystocia in our study mares. These findings contrasted with those of another study²² in which only 5 of 9 mares in which a fetotomy was performed survived to discharge. The disparity may be a result of differences in the way the participant mares were selected or in the skill of the veterinarians who performed the fetotomy. In the study reported here, fetotomy was performed immediately after mares were examined for fetal viability; therefore, manipulations of the fetus in the birth canal were minimized. However, it could not be determined with certainty from the records that there had been no preceding attempts at manipulation. Results of fetotomy vary and depend on a veterinarian's experience and the facilities available^10,17,23; however, our results support the conclusion that this technique can be efficacious.

Short-term fertility rates in mares after fetotomy in the study reported here were not significantly different from those in mares that gave birth naturally to a foal at the veterinary school breeding farm or rates reported for nontreated mares in research conditions.^24,25 In 1 study,²² 59% of mares treated because of dystocia and bred in the same year gave birth to live foals the following year; however, this rate cannot be compared with our results because we only recorded the 45-day pregnancy rate.

Fetotomy performed promptly on a nonviable fetus by a skilled veterinarian may permit avoidance of unnecessary cesarean section in mares. Fetotomy should be considered a viable option for safe and quick correction of fetal malposture with a low risk of fatalities and no ill effects on short-term fertility, but these results depend on the obstetric skills of the attending veterinarian.