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- 258 2009 ր Vol. 55 ր AAEP PROCEEDINGS PREGNANT MARE 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.