Fortunately, the incidence of twin pregnancies identified after Day 35 to 40 in mares is low, and veterinary practitioners are infrequently required to deal with twin pregnancies in mares beyond Day 35 to 40. Nonetheless, the high rate of abortions, poor neonatal viability, growth-retarded fetuses, dystocia and reduced fertility in mares subsequent to twin abortions necessitates that twin pregnancies that are identified after Day 40 be managed in order to avoid these consequences. Several methods have been utilized in attempts to reduce twin pregnancies detected during the fetal stage of pregnancy in mares. These methods include acute nutritional deprivation, transvaginal ultrasound guided puncture of the conceptus, manual trauma or ballottement of the fetus, surgical removal of the conceptus, and transabdominal ultrasound guided injection of the fetus. This paper will focus only upon the use of transabdominal ultrasound-guided fetal puncture as a method to reduce twin pregnancy in mares. Transabdominal ultrasound-guided letal puncture for twin reduction was originally reported by Rantanen and Kincaid in 1988. In the original description of the technique, a fetal intracardiac injection of potassium chloride was used to induce death of one fetus. Although effective, this approach is more technically challenging, as it requires accurate placement of the KCl into the fetal vascular space in order to induce cardiac arrest. Subsequently, McKinnon and Rantanen described the use ofprocaine penicillin G for intrafetal injection in order to induce fetal death. This technique does not require precise placement of the material in the fetal vascular space and fetal death can be induced by placement of the PPG into either the fetal thorax or abdomen. Careful evaluation of the twin pregnancy by transabdominal evaluation can be conducted with either a 5.0-mHz or 3.0-mHz transducer. Many twin pregnancies between 90 to 130 days will be imaged in the caudal abdomen, just cranial to the udder; however, sedation of the mare, particularly with acepromazine, results in a profound uterine relaxation. After sedation or administration of clenbuterol, the fetal location often shifts cranially. The equine fetus is remarkably mobile during this stage of pregnancy and both fetuses can rotate freely from cranial to caudal presentation. Size may be the best discriminator if there is a detectable difference in the size between the two fetuses. If not, relative location should be determined, but keep in mind that these locations will change. After the fetuses have evaluated for size, location and fetal heart rate, the mare is given clenbuterol to induce uterine relaxation and improve access to the fetus via the ventral body wall. Detomidine and butorphanol are used as a sedative/analgesic for this procedure. Once the fetal parameters have been established, and the twin for reduction has been selected, the ventral abdomen overlying the twin is surgically prepared. In addition to the sedation and analgesia, a local infiltration of lidocaine is used to provide analgesia at the puncture site. Although injection of the fetus may be accomplished via a "free-hand" procedure using ultrasound, we prefer a 3.5-mHz ultrasound transducer fitted with a biopsy guide. An 18-gauge, 8-inch spinal needle with stylet can be used for most fetal injections. Once the fetal thorax is visualized, the needle in introduced through the skin, abdominal wall and uterus into either the fetal thorax or abdomen. Injection of 10 to 20 ml of procaine penicillin G is used to induce fetal death. Intrafetal injection (into either the abdomen or thorax) does not result in immediate death of the injected fetus. In some cases, fetal death was not detected (confirmed) until the day following the injection. Mares that are candidates for transabdominal fetal twin reduction are treated with oral Altrenogest (beginning on the day of the procedure) as well as flunixin meglumine. Oral altrenogest is continued until the recheck examination two weeks after the procedure. The benefits of supplemental progestin therapy are uncertain, and some authors suggest equal success without the use of supplemental progestin. If mares are placed on supplemental progestin, it is imperative that periodic monitoring of fetal viability be conducted to ensure that two dead fetuses are not retained in utero because of the exogenous progestin therapy - a circumstance that we have observed in one of our clinical cases. Most pregnancy losses subsequent to this procedure occurred within two to four weeks after the procedure. Outcome: Success rates (measured as viable singleton foals born at term) vary across publications with this technique. In our practice approximately 50% of the procedures are successful (survival of a single fetus to term); however there remains a significant incidence of foals born with significant in utero growth retardation subsequent to this procedure.
|Translated title of the contribution||Transabdominal reduction of equine twin pregnancies|
|Number of pages||5|
|State||Published - Sep 2006|
- Twin pregnancy
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