PREGNANT MARE

Success Rate of Post-Fixation Twin Reduction Using Cranio-Cervical Dislocation

Karen E. Wolfsdorf, DVM, Diplomate ACT; Dwayne Rodgerson, DVM, MS, Diplomate ACVS; Richard Holder, DVM; and Angela Schoergendorf

Cranio-cervical dislocation is a good option in the management of post-fixation twins, producing a single normal sized healthy foal in 63.16% of cases. Authors’ addresses: Hagyard Equine Medical Institute, 4250 Iron Works Pike, Lexington, Kentucky 40511 (Wolfsdorf, Rodgerson, Holder); and Department of Agriculture, University of Kentucky, Lexington, Kentucky 40502 (Schoergendorf); e-mail: [email protected] (Wolfsdorf). © 2009 AAEP.

1. Introduction foals are usually weaker, more susceptible to infec- The establishment and loss of twins, after 35 days of tion, and slower to develop than singletons. gestation, often results in a mare that is barren for Although pregnancies can be diagnosed with ul- a year and the associated economic loss. The inci- trasound as early as 9 days after ovulation, twin dence of twin births in the past has been docu- pregnancies are optimally detected between days 13 mented as occurring in 1–2% of the equine and 15 of gestation when the embryonic vesicles are population,1 with twinning accounting for 6–30% of still mobile and two embryonic vesicles can be im- 7–9 abortions in the mare.2–4 Abortion or still birth re- aged. Natural twin reduction does not occur be- sulted in 64.5% of twin conceptuses that were main- fore day 11, and it is negligible between days 11 and tained for Ն8 mo, with only 14% of surviving foals 15.8,10,11 Therefore, twin pregnancies that are de- reaching the second week of neonatal life.2 In an- tected during the mobility phase (days 9–15) are other study, only 11% of 130 mares carrying twins best managed by manually crushing one embryonic produced viable foals, and only 38% of these mares vesicle.6 The smaller vesicle or the vesicle that needs produced viable foals the following year.5 When the least amount of uterine manipulation is prefer- twins are present, gestation proceeds normally until entially destroyed.12 Survival rates of the remaining the conceptuses begin to compete for uterine space vesicle exceeded 90%.12 or placenta. With or without mummification, After fixation of the embryonic vesicles between death of one fetus leads to abortion, usually between 16 and 17 days of gestation, the success rate of 5 and 9 mo of gestation.6 Lactation commonly occurs reducing the twins to a viable singleton varies tre- after one foal dies, causing premature mammary mendously among procedures. Whether twin em- gland development.6 If one or both foals are born bryonic vesicles fix unilaterally (70%) or bilaterally alive, the mare may require assistance. Surviving is important for natural reduction. Ginther13 de-

NOTES

AAEP PROCEEDINGS ր Vol. 55 ր 2009 257 PREGNANT MARE termined natural reduction to a single conceptus to branes, operator experience in not damaging the adja- occur ϳ83% for unilateral fixation as opposed to cent vesicle or traumatizing the uterus excessively minimal reduction (4%) when fixed in different during penetration of the needle, and leakage of fluid horns. If there is bilateral fixation, and natural from the aspirated vesicle can cause separation of reduction with early fetal loss does occur, it seems to placental membranes from the endometrium.21,22 be temporally related to the apposition of allanto- Transcutaneous ultrasound-guided twin reduction in chorions between fetuses. The actual mechanism the mare has been performed between days 66 and 168 is not known.14 of gestation. This procedure injects potassium chlo- In addition, the probability of natural reduction ride (KCL) into the heart of the smaller fetus, with occurring decreases as gestational age increases to 38–40% of mares delivering a normal single live day 40.12,15 If natural reduction does not occur af- foal.21,23 Subsequent twin reductions have concluded ter fixation, manual reduction of unilaterally fixed that the procedure is best performed between 115 and twins is difficult without damaging both conceptus. 130 days of gestation, resulting in 49% delivering a If the vesicles can be separated, 90% of unilateral single live foal or 60% when injecting procaine penicil- twins can be manually crushed successfully between lin instead of KCl.17 Unfortunately, the success of days 17 and 20.16,17 Manual reduction of bilateral this procedure depends heavily on the experience of twins at days 16–40 is a necessity if abortion at a the operator and preventing iatrogenic infection or later stage of gestation is to be avoided. Seventy- prostaglandin release. Additionally a proportion of five percent of bilateral twins may be successfully the single live foals that are born seem to have some reduced to a singleton pregnancy by crushing one degree of placental insufficiency being weak, small at vesicle before day 30 of gestation.16,17 However, birth and unthrifty and many times a lot of expense is with bilateral twins of gestational age Ͼ35 days, invested in a foal that is of little value, especially if there is a greater risk of abortion of both at later they are a colt.21 stages.1,16 It has been speculated that this may be From the above literature, it is evident that no caused by fluid release and loss of chorioallantoic procedure is considered to be consistent or success- and endometrial contact.4 ful enough to be optimal (Table 1). In 2001 a new Other methods to reduce twins before and during technique described as cranio-cervical dislocation the fetal stage (day 40) and endometrial cup forma- (CCD) was first used for fetal reduction at Hagyard tion (day 36) have included the following: between Equine Medical Institute (HEMI) when twins were days 21 and 49 of gestation, sudden temporary re- presented at 55–150 days of gestation. CCD is the duction of food intake by mares for 2–4 wk with a dislocation of the first cervical vertebrae from the 60% chance of reduction18; manual manipulation cranium, disrupting the ligamentous attachments trans-rectally without vesical rupture between 28 and severing the spinal cord. The basis for this and 42 days with a 28% single viable foal13; surgical procedure is to eliminate one twin before placental removal of one conceptus between 41 and 65 days of formation is complete, allowing the remaining fetus gestation with five of eight mares with bilateral to use the entire endometrial surface for nutrient fixation delivering a single foal and zero of seven and oxygen exchange and to grow to its full poten- mares with unilateral fixation produced a viable tial. CCD can be performed trans-rectally or intra- foal4; trans-vaginal ultrasound guided aspiration of abdominally using standing flank incision.24 When the allantoic fluid of one conceptus between days 20 performed trans-rectally, the procedure is done be- and 71 with results varying between unilateral tween days 55 and 90 of gestation when the fetus twins (33%) or bilateral (75%). When the proce- can still be reached and identified, whereas the in- dure was performed on unilateral twins before day tra-abdominal approach can be performed from days 36, 40% of mares had a viable singleton 10 days later 58 to 110 of gestation, after which the development as opposed to only 10% after day 35.19 In a subse- of the fetal bones and muscles prevent dislocation. quent study, 31% of unilateral twin reduction pro- A miniature donkey fetus was able to be manipu- duced live foals with all successful procedures being lated at 150 days. A retrospective study was there- performed before 35 days of gestation.20 fore performed to look at the success rate of Further results have been conflicting, with 0–9% producing a single normal-sized healthy foal using single live foal delivered in unilateral twins depending CCD using the standing flank intra-abdominal or on gestational age and 25% of bilateral twins having a the trans-rectal approach at HEMI between 2001 single viable foal.21 In most cases, fetal death of the and 2008. remaining twin if it occurred was noted 10–14 days after the procedure; however, some aborted 3–9 mo 2. Materials and Methods later.21 It has therefore been concluded that trans- Eight Thoroughbred mares of varying ages and par- vaginal ultrasound guided twin reduction is best per- ity between 55 and 90 days of gestation were pre- formed before day 35 of gestation.22 A variety of sented to HEMI for CCD using trans-rectal factors that influence the success and limitations of manipulation. The mares were restrained in this procedure include: day of gestation at time of stocks or twitched in the doorway. Sedation using reduction, unilateral versus bilateral fixation caused detomidine HCLa (10–20 mg/kg, IV) was adminis- by close proximity of the fetuses and associated mem- tered as needed. Care should be used with seda-

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Table 1. Treatment Regimens for Reducing Twins

Method Gestational Age Success Rate

Pinch twin 11–15 days Ͼ90%12 Natural reduction Unilateral 17–40 days 83%13 Bilateral 17–30 days 4%13 Manual crushing Unilateral (separated) 17–20 days 90%16,17 Bilateral 17–30 days 75%16,17 Reduced food intake 21–49 days 60%13 Manual manipulation (without vesicle rupture) 28–42 days 28%13 Surgical removal Unilateral 41–65 days 0%4 Bilateral 41–65 days 62%4 Transvaginal ultrasound-guided aspiration Unilateral Յ36 days 31–40%19 Unilateral Ͼ36 days 10%21 Bilateral 20–71 days 25–75%19,21 Transcutaneous ultrasound-guided injection Potassium chloride 66–168 days 38–49%21,23 Procaine penicillin 115–135 days 60%17 CCD Transrectal 60–90 days 63% Intra-abdominal 58–150 days 63.10%

tion, because the uterus may relax, and the fetuses for a month to establish normal growth of the con- may move cranially in the abdomen and out of reach. tinuing fetus and demise of the other. Relaxation of the smooth muscle in the uterus and If trans-rectal reduction could not be achieved or rectum is very important and can be achieved by the attempted, intra-abdominal reduction through a administration of propantheline bromideb (30 mg, flank approach was performed. To date, this stand- IV), allowing easier identification and manipulation ing procedure through a flank incision has been used of the fetuses. To help inhibit prostaglandin re- for 38 sets of twins between gestational ages of 58 lease, flunixine meglaminec (1 mg/kg, IV) was ad- and 150 days including 33 Thoroughbred mares, 4 ministered before the procedure. The smaller fetus Standardbred mares, and 1 miniature donkey. or the fetus that had less contact with the endome- Trans-abdominal ultrasound was used to identify trium and minimal space to grow was preferentially the horn in which the most viable fetus was located, reduced. This fetus is usually identified in the as determined by fetal size and by fetal position with more cranial aspect of the uterine horn in unilateral the greatest surface area for attachment to the en- twins. Once the identified fetus was located, the dometrium. In unilateral twins, the fetus in the head was isolated by finding the dome shape and most cranial aspect of the uterine horn should be palpating the mandible or moving caudally to locate selected for reduction. A standing flank laparot- the cervical vertebrae. CCD was performed by sta- omy was performed ipsilateral to the horn contain- bilizing the head between the thumb and forefinger ing the fetus that had been identified for reduction. and bending the head from side to side. Preoperative medications include propantheline This damages the ligaments attaching the head bromideb (30 mg, IV), flunixin meglaminec (1 mg/kg, and neck. Dislocation is created by placing the IV), procaine penicillin Ge (22,000 mg/kg, IM, q 12 h) thumb at the base of the cranium and applying and gentocin sulfatef (6.6 mg/kg, IV, q 24 h). Pro- pressure proximal and dorsally. panthentheline bromide is essential for relaxing and A distinctive pop was felt when dislocation was preventing uterine contractions while finding and achieved, and the thumb and forefinger could be manipulating the fetus. Identification of the pre- placed in the space created between the head and ferred uterine horn was not always possible, because neck. Further crushing or damage to the cranium of fetal movements and imaging capabilities. was attempted if continued isolation of the fetus was When this occurred, the authors’ preferred to make attained. Mares were placed on altrenogestd (0.088 an incision on the right flank of the mare, allowing mg/kg, OS, q 24 h) for 3–4 wk. After CCD was easier access to the reproductive tract without intes- performed trans-rectally, death with loss of the fetal tinal interference. Both horns are still accessible heartbeat was monitored and usually occurred 24 h from one side because of the width of the mare’s to 3 wk after the procedure. Fetal viability was abdomen. The uterus was located within the ab- evaluated when possible 1 wk later and every 2 wk dominal cavity with one arm, and the twin was

AAEP PROCEEDINGS ր Vol. 55 ր 2009 259 PREGNANT MARE isolated as described for trans-rectal dislocations. CCD was performed by manipulating the fetus in- tra-abdominally through the uterus, without incis- ing or invading the uterine lumen. The flank incision was routinely closed. Mares were placed on flunixine meglaminec (1 mg/kg, IV, q 12 h), procaine penicilline (20–50 IU/kg, IM, q 12–24 h), and gentocin sulfatef (6.6 mg/kg, IV or IM, q 24 h) for the next 2 days, and then trimethoprin sulphag (24 mg/kg, OS, q 12 h) for 1 wk and altrenogestd (0.088 mg/kg, OS, q 24 h) for the next month. Re- evaluation of fetal viability was performed with Figure 1. The success rate per year to produce a single normal trans-rectal or trans-abdominal ultrasonography ev- size healthy foal. ery 2 wk until the death of one twin was observed. Unfortunately, many mares were lost to follow-up evaluation, and information on whether the mare had a normal-sized healthy foal, aborted, or was the effect of gestational age was not significant on found empty at some point in gestation were the outcome. only results obtained. Statistical analysis was performed using SAS 9.2. 4. Discussion The FREQ procedure was used to determine the Signs of impending death of a fetus include loss of frequency of success and failure. The MEANS pro- thoracic shape, with the fetus becoming more con- cedure determined the mean gestational age for suc- vex; loss of definition of abdominal organs; and ir- cess or failure, and the logistic procedure regular, weak heartbeats. Placentas from mares determined the effect of gestational age on outcome. delivering singleton foals have a small sack attached Other comparisons could not be made because of to the allantoic surface. The nonviable fetus is incomplete data. marsupialized forming a small pouch, with a stalk protruding from the allantoic surface. This pouch 3. Results contains the mummified fetal bones. Examination of the chorionic surface reveals minimal evidence Eight sets of twins were reduced with trans-rectal that a twin was present, with microvilli present manipulations, with gestation lengths between 55 along the entire attachment of the placenta. and 90 days. Five of the eight mares (63%) deliv- CCD has advantages compared with other proce- ered a single fetus of normal size. Three mares dures for reducing post-fixation twins. Results us- aborted both fetuses between 30 and 60 days after ing this procedure have a better outcome than the procedure was performed. No viable heartbeat transcutaneous, ultrasound-guided reductions in was observed in the reduced fetus between 24 h and which a large percentage of single foals have been 3 wk after cranio-cervical dislocation. Unfortu- undersized and weak.h Outcomes of the different nately, the trans-rectal procedure is technically dif- procedures may be affected by the time of reduction. ficult, and multiple manipulations of the fetus are Other procedures have not been successful at the sometimes necessary before dislocation is achieved. stage of gestation (55–110 days) in which cranio- Of the eight mares, three mares had multiple manip- cervical dislocations are performed. Transcutane- ulations of a fetus; only one of these mares aborted. ous, ultrasound-guided reductions are done later in However, we have not determined whether addi- gestation than CCDs, and placental function and tional manipulations result in a detrimental effect growth may be limited when twin reductions occur on the remaining conceptus. later in gestation. When performing CCDs at a CCDs, using the intra-abdominal surgical proce- later stage of gestation than trans-vaginal ultra- dure, produced a single normal healthy foal in sound-guided aspirations, the uterus is not punc- 63.16% (24/38) of mares. Success rates varied from tured with a needle, and fluid does not leak from the 50% (1/2) in 2003, 66.66 (2/3)% in 2004, 60% (6/10) in reduced conceptus, potentially disrupting the fetal 2005, 58.33% (7/12) in 2006, and 72.73% (8/11) in membranes of the remaining conceptus. Conse- 2007 (Fig. 1). With this technique, death of the quently, oxygenation and nutrient exchange of the manipulated twin was evident from 1–8 wk after remaining conceptus can be compromised.5,21 Con- the procedure. One fetus that underwent CCD currently not transversing the abdomen and pene- never died, and abortion was induced at 7 months to trating the lumen of the uterus reduces the chance not affect the mare’s present or future fertility. of bacteria contamination resulting in a placentitis. Gestational age at time of procedure ranged from 58 Disadvantages of CCD mostly pertain to isolation to 150 days, with no significant difference (p ϭ of the fetus. When the mare is at this stage of 0.913) between mean gestational age for a single gestation, identifying the correct fetus within the normal healthy foal (79.90 Ϯ 19.93 days) compared uterus is similar to “bobbing for apples.” It is ab- with loss of both (80.15 Ϯ 10.21 days). In addition solutely imperative that the uterus is relaxed

260 2009 ր Vol. 55 ր AAEP PROCEEDINGS PREGNANT MARE enough for identification of fetal anatomy. No doc- 8. Giles R, Donahue J, Hong C, et al. Causes of abortion, umented evidence is available at this time of gesta- stillbirth, and prenatal death in horses. J Am Vet Med Assoc 1993;8:1170–1175. tion regarding the extent of trauma or prostaglandin 9. Pascoe, R. Methods for the treatment of twin pregnancy in release that occurs with manipulation of the fetus the mare. Equine Vet J 1983;15:40–42. through the uterus, although previous studies have 10. Roberts C. Termination of twin gestation by blastocyst shown 20 min of uterine manipulation is necessary crush in the broodmare. J Reprod Fertil Suppl 1982;32: for significant prostaglandin release.12 The proce- 447–449. 11. Ginther OJ. Ultrasonic imaging and reproductive events in dure is relatively rapid from isolation of the fetus to the mare. Cross Plains, WI: Equiservices, 1986. CCD; therefore, severe inflammation should not re- 12. Ginther OJ. Twin embryos in the mare: 1. From ovula- sult, but proficiency and time of manipulations may tion to fixation. Equine Vet J 1989;21:166–170. affect the outcome. The incision site of the flank 13. Ginther OJ. The nature of embryo reduction in mares with twin conceptuses: deprivation hypothesis. Am J Vet Res laparotomy heals with few complications. When a 1989;50:45–53. seroma or cellulites develops the incision can be 14. Ginther O, Griffen P. Natural outcome and ultrasonic iden- opened on the ventral end and drained. The dura- tification of equine fetal twins. Theriogenology tion of time that the manipulated fetus survives is 1994;41:1193–1199. inconsistent, and an explanation is unknown.24 15. Ginther OJ. Postfixation embryo reduction in unilateral and bilateral twins in mares. Theriogenology 1984;22: With a success rate of 63.16% to produce a single 213–223. normal-sized healthy foal, this procedure has a 16. Bowman T. Ultrasonic diagnosis and management of early higher success rate than other procedures, which twins in the mare, in Proceedings. 32nd Annual Convention makes it a viable alternative for twin reduction after of the American Association of Equine Practitioners 1986; 35–43. fixation. 17. McKinnon A, Rantanen N. Twins. In: Rantanen N, Mc- Kinnon A, eds. Equine diagnostic ultrasonography. Balti- 5. Summary more, MD: Williams and Wilkins, 1998;141–156. 18. Merkt H, Jungnickel S, Klug E. Reduction of early twin At this time, CCD seems to be the most promising pregnancy to a single pregnancy in the mare by dietetic method to obtain a single, normal-sized, healthy foal means. J Reprod Fertil Suppl 1982;32:451–452. when twins are detected after fixation. In addition, 19. Bracher V, Parlevliet J, Pieterse M, et al. Transvaginal none of the reviewed procedures (natural reduction, ultrasound-guided twin reduction in the mare. Vet Rec 1993;133:478–479. dietary restriction, trans-vaginal, and trans-abdom- 20. Jonker F, Parlevliet J, Vos P. Twin reduction in sixteen inal ultrasound-guided injections and CCD) provide mares by transvaginal ultrasound-guided puncture of the a method to unequivocally produce a healthy, nor- embryonic vesicle, in Proceedings. Brit Eq Vet Assoc Annual mal-sized singleton. Therefore, at this time, the Congress 1995. 21. Macpherson ML, Reimer JM. Twin reduction in the mare: best solution is still to manually reduce twins early current options. Anim Reprod Sci 2000;60–61:233–244. in gestation, before mobility has ceased. 22. Macpherson ML, Homco LD, Varner DD. Transvaginal ul- trasound-guided allocentesis for pregnancy elimination in the mare. Biol Reprod Monogr 1995;1:215–223. References and Footnotes 23. Rantanen NW, Kincaid B. Ultrasound guided fetal cardiac 1. Pascoe RR, Pascoe DR, Wilson MC. Influence of follicular puncture. A method of twin reduction in the mare, in Pro- status on twinning rate in mares. J Reprod Fert Suppl ceedings. 34th Annual Convention of the American Associ- 1987;35:183–189. ation of Equine Practitioners 1988;173–179. 2. Ginther OJ, Bergfelt, DR. Embryonic reduction before Day 24. Wolfsdorf K, Rodgerson D, Holder R. How to manually re- 11 in mares with twin conceptuses. J Anim Sci 1988;66: duce twins between 60–120 days gestation using cranio-cer- 1727–1731. vical dislocation, in Proceedings. 51st Annual Convention 3. Pascoe D, Pascoe R, Hughes J, et al. Comparison of two of the American Association of Equine Practitioners 2005; techniques and three hormone therapies for management of 284–287. twin conceptuses by manual embryonic reduction. J Reprod Fertil Suppl 1987;35:701–702. aDormosedan; Orion Corporation, Espoo, Finland. 4. Pascoe DR, Stover SM. Surgical removal of one conceptus bPropantheline bromide; Compounded Hagyard Pharmacy, from fifteen mares with twin conceptuses. Vet Surg 1989; Lexington, KY 40511. 18:141–145. cBanamine; Schering-Plough Animal Health, Union, NJ 07083. 5. Pascoe DR, Stover SM. Surgical removal of one conceptus dRegumate; Intervet, Millsboro, DE 19966. from fifteen mares. In: Ginther OJ,eds. Reproductive bi- eProcaine Penicillin; Butler Animal Health Supply, St. Joseph, ology of the mare. Cross Plains, WI: Equiservices, 1979. MO 64503. 6. Jeffcott LB, Whitwell KW. Twinning as a cause of neonatal fGentafuse; Butler Animal Health Supply, St. Joseph, MO loss in the Thoroughbred. J Comp Pathol 1973;83:91–105. 64503. 7. Roberts SJ. Veterinary obstetrics and genital diseases, 2nd ed. gTrimethoprim sulfa; Interpharm, Hauppauge, NY 11788. Ithaca, NY: Woodstock, 1986. hJohanna Reimer. Personal communication. April 2001.

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