Success rates of various techniques for reduction of twin pregnancy in mares

Twin Pregnancy in the Martina Franca Donkey Breed Managed by Natural Reduction and Post-Fixation Manual Crushing

In Equids, undetected twin pregnancy represents the most important cause of abortion and is also associated with high neonatal mortality rates. Therefore, the detection and management of twin pregnancies is pivotal to allow the continuation of single pregnancies. Although pre-fixation manual crushing of one embryo is the most common management of twin pregnancies, and the impact of natural reduction has been reported in mares, very little is known about donkeys. The present study aimed to report results on the natural reduction occurrence and post-fixation manual crushing management of twin pregnancies in the Martina Franca donkey breed.

METHODS

Twenty-five twin pregnancies were detected at 11-13 days after ovulation. At 16 days after ovulation, twin pregnancies were classified as unilateral or bilateral and left untreated. The occurrence of natural reduction of one embryo was assessed at 20-21 days after ovulation, and post-fixation manual crushing of one embryo was performed in those cases in which natural reduction did not occur. The pregnancy rate at 28 days after ovulation and live foal rate were recorded.

RESULT

Sixteen out of 25 twin pregnancies were unilateral and nine bilateral. At 20-21 days after ovulation, the natural reduction of one embryo occurred in 87.5% of the unilateral and in none of the bilateral twin pregnancies. The remaining twin pregnancies were treated by post-fixation manual crushing of one embryo. The 28-days-after-ovulation single embryo pregnancy rate was 93.8% for unilateral twin pregnancies and 88.9% for bilateral twin pregnancies, with an overall pregnancy rate of 92%. The live foal rate was 87%.

CONCLUSIONS

The success rate of natural reduction within 20-21 days after ovulation, the 28-days-after-ovulation pregnancy rate, and the live foal rate suggest that waiting for the natural reduction of one embryo and choosing the post-fixation manual crushing of one embryo could be considered as an alternative to traditional early pre-fixation manual crushing in the Martina Franca donkey breed.

A case of a twin surviving to term following the abortion of its co-twin at 9 months in an Arabian mare

Twin pregnancy in mares is one of the leading causes of abortions. Abortion invariably impacts both fetuses. This report describes an unusual case of a twin surviving to term following the abortion of its co-twin at 9 months in a 7-year-old Egyptian Arabian mare. At the time of abortion at 9 months of gestation, the size of the aborted fetus was equivalent to one of approximately 5 months of age while the age of the live co-twin was 9 months. Both fetuses were males. A skin sample was collected from the aborted fetus and hair samples were collected from the dam, sire and live foal for parentage analysis. The parentage analysis confirmed that both fetuses were by the same dam and sire stallion. The authors suggest several scenarios to explain this condition. This report describes a unique case of a twin surviving to term following the abortion of its co-twin at 9 months in a mare.

An Overview of Infectious and Non-Infectious Causes of Pregnancy Losses in Equine

Equine breeding plays an essential role in the local economic development of many countries, and it has experienced rapid growth in China in recent years. However, the equine industry, particularly large-scale donkey farms, faces a significant challenge with pregnancy losses. Unfortunately, there is a lack of systematic research on abortion during equine breeding. Several causes, both infectious and non-infectious, of pregnancy losses have been documented in equines. The infectious causes are viruses, bacteria, parasites, and fungi. Non-infectious causes may include long transportation, ingestion of mycotoxins, hormonal disturbances, twinning, placentitis, umbilical length and torsion, etc. In current review, we discuss the transmission routes, diagnostic methods, and control measures for these infectious agents. Early detection of the cause and appropriate management are crucial in preventing pregnancy loss in equine practice. This review aims to provide a comprehensive understanding of the potential causes of abortion in equines, including infectious agents and non-infectious factors. It emphasizes the importance of continued research and effective control measures to address this significant challenge in the equine industry.

Success rates and factors influencing pregnancy outcome after 464 transvaginal ultrasound-guided twin reductions in the mare

BACKGROUND

Transvaginal ultrasound-guided aspiration (TUA) is used for post-fixation twin reduction in mares. However, there is limited information regarding factors that influence pregnancy outcome after TUA.

OBJECTIVES

To evaluate the effect of day of gestation on which TUA is performed, aspiration volume, puncture of the conceptus, medication administered before and after TUA, embryo location, mare age and parity and operator experience on pregnancy and foaling rates after TUA.

STUDY DESIGN

Retrospective case series.

METHODS

Data were collected from case records of 464 TUAs performed by 14 operators in 422 mares diagnosed pregnant with dizygotic twins in two different facilities between 2010 and 2019. Pregnancy status was determined by ultrasonography at 5-7 days and 3-4 weeks after the TUA was performed. Subsequent pregnancy and foaling results were obtained by follow-up communication. The effects of mare, gestation- and TUA-related variables on pregnancy and foaling rates were analysed by the chi-square-test for homogeneity and Fisher's exact test and logistic regression.

RESULTS

TUA was performed between 21 and 82 days of gestation in unilaterally (267/359 [74.4%]) and bilaterally fixed (92/359 [25.6%]) twin pregnancies. A singleton pregnancy (218/381 [57.2%]), persistent twin pregnancy (60/381 [15.8%]), or the loss of both conceptuses (103/381 [27%]) was confirmed 5-7 days after TUA was performed. At 3-4 weeks post TUA 50.3% (163/324) of mares were diagnosed with a single viable pregnancy and 40.1% (127/317) went on to deliver a live single foal. TUA performed early in gestation (D 25-35) resulted in the birth of a live singleton foal in 49.3% (74/150) of mares.

MAIN LIMITATIONS

Missing retrospective data despite extensive follow-up.

CONCLUSION

This is the first large scale study to demonstrate that acceptable pregnancy and foaling rates can be achieved in mares diagnosed with twins when TUA is performed early in gestation (<40 days).

Ultrasound-guided fetal thorax compression to reduce post-fixation twins in the mare

BACKGROUND

Management of twin pregnancy after conceptus vesicle fixation in the horse is challenging because the reduction techniques described are either invasive, difficult to perform or associated with disappointing success rates.

OBJECTIVES

To evaluate the success of transrectal ultrasound-guided fetal thorax compression for reducing post-fixation twin pregnancy in mares.

STUDY DESIGN

Retrospective clinical study.

METHODS

Sixteen mares were presented for twin reduction between 51 and 79 days of gestation. History obtained from the owner and/or referring veterinarian detailed information regarding the mare (age, breed), pregnancy (day of gestation, dizygotic versus monozygotic twins, unilateral versus bilateral fixation), treatment and outcome (one live fetus at discharge; live singleton at foaling) after twin reduction. Transrectal fetal thorax compression was performed under ultrasound guidance by two experienced operators.

RESULTS

Overall 9 of 16 twin pregnancies were successfully reduced and the likelihood of success was significantly higher in dizygotic than monozygotic twins. The procedure was successful in 9 of 10 dizygotic twins but unsuccessful in all six cases of monozygotic twins. Among the dizygotic twins, two mares lost the pregnancy after discharge from the clinic, seven mares delivered a healthy foal of normal size.

MAIN LIMITATIONS

Small case number.

CONCLUSIONS

Transrectal ultrasound-guided fetal thorax compression is a minimally-invasive and successful technique for reducing dizygotic twin pregnancies at approximately 2 months of gestation, but does not lead to any live births in cases of monozygotic twins.

Sexing of Embryos at the Time of Twin Reduction: A Clinical Approach

This study provides new unique information on bovine twin pairs during the late embryonic period (28-34 days of pregnancy) in relation to (1) a predictive ultrasound measurement that was differential for sexing heterosexual twins; (2) intrauterine embryonic growth patterns in twin pairs; and (3) a higher vulnerability of female embryos compared to males following an induced embryo reduction in heterosexual twins. The study population comprised 92 dairy cows carrying bilateral twins. A length difference between co-twins equal to or greater than 25% in around 50% of pregnancies served to determine the sex of embryos with 100% accuracy in heterosexual twins, which was assessed four weeks later on the remaining fetus after twin reduction. The apparent rates of growth of twin pairs and of individual male and female embryos from day 28 to 34 of gestation were similar to established growth pattern standards for singletons. Mean embryo sizes in relation to gestational age were smaller by some 5 days' growth equivalent in twins compared to singletons. After the reduction in the female embryo in heterosexual twins, the risk of male embryo loss was null. This new information allowed for sex selection at the time of twin reduction.

Luteal tissue area and immunoreactive concentrations of progesterone in plasma of bred and non-bred mares

Progesterone is pivotal to maintain pregnancy in the first trimester and low concentrations (<4 ng/mL) have been associated with early pregnancy loss. Measurement of progesterone is widely used in practice to determine whether a mare needs progestin supplementation. Therefore, the objective of the present study was to determine progesterone concentrations and the luteal tissue area in mares non-bred, and those bred becoming pregnant, and those failing to become pregnant. We hypothesized that pregnant mares have greater progesterone concentrations than non-pregnant mares. Fifty-two cycles of mares (n=14) were monitored by ultrasonography every other day until detection of a preovulatory follicle. Then deslorelin acetate was administered to induce ovulation. Twenty-four hours later, mares were bred (∼2 billion progressively motile sperm extended in 50 mL; n=37 cycles) or a sham-bred (50 mL of extender; n=15 cycles). Ovulation was confirmed and number of corpora lutea and the luteal tissue area were recorded daily until 10d post-ovulation. Progesterone concentrations were assessed daily from the day of the ovulation up to 10d post-ovulation. Pregnancy diagnosis was carried out at 10d and 13d post-ovulation. Of the bred mares, 20 of them became pregnant and 17 did not. Data were analyzed with a mixed model, Tukey test as post-hoc, and Pearson's coefficient of correlation. Progesterone concentrations and luteal tissue area varied with time (P=0.001) but not with group (P>0.05). Multiple ovulations were associated with greater progesterone concentrations and luteal tissue area (P=0.0001). There was a moderate positive association between the number of ovulations and luteal tissue area (r=0.54; P=0.0001). The lack of change in the progesterone concentration and luteal tissue area between bred and non-bred mares suggests that horse seminal plasma does not affect luteal function in mares. As all mares had progesterone above 4 ng/mL after 5d post-ovulation; it is possible that if mares with abnormal progesterone concentrations were used, the results could have been different. In conclusion, pregnancy was not associated with greater progesterone concentrations or luteal tissue area.

A retrospective study of twin pregnancy management in mares

The aim of the study was to compare three methods of reducing twin pregnancy in mares to maintain a single pregnancy. As multiple pregnancies in mare are always undesirable, early ultrasound diagnosis makes possible management of twin pregnancies and extra embryo removal. In years 2010-2018, 16494 mares were sonographically tested for early pregnancy, finding 868 cases of twins (471 bilateral and 397 unilateral). 260 mares with a confirmed bilateral tween pregnancy were subjected to manual crushing of one embryo and administration of flunixin at a dose of 1.1 mg/kg BW. 186 mares were subjected only to the embryo crushing procedure. 25 mares from this group were on a restrictive diet. In the unilateral twin pregnancy mare group, 62 were subjected to manual embryo reduction with simultaneous treatment with flunixin, 60 had only manual embryonic vesicle crush and 210 had a restrictive diet. Determination of success, measured as the development of a single pregnancy, were monitored 2 weeks after the procedure, between the 50th and 60th day of pregnancy and after the 90th day of pregnancy. In general, warm-blooded mares were more prone to a twin pregnancy, and at the same time, all the procedures used to reduce it to a single pregnancy caused a greater risk of losing both embryos than in the case of cold-blooded mares. The beneficial effect of administering flunixin after manual removal of one embryo on the maintenance of the other has been experimentally proven in both unilateral and bilateral twin pregnancy.

Twins in Dairy Herds. Is It Better to Maintain or Reduce a Pregnancy?

Simple Summary

In dairy herds, twin or other multiple pregnancies are not desirable as they compromise the health and productive lifespan of the cows. The mean productive lifespan of primiparous and secundiparous dairy cows delivering twins is about 300 and 200 days shorter, respectively, than that of cows delivering singletons. In addition, the long-term negative effects of twinning are not limited to the early lactation but continue for a period of up to 800 days after calving. Herd management options after diagnosing a twin pregnancy are discussed from an animal health and economic perspective.

Abstract

Multiple ovulations and so multiple pregnancies have increased recently in dairy cattle. The incidence of the double ovulation impact in high producers at insemination may be over 20%. Twin pregnancies are undesirable as they seriously compromise the welfare and productive lifespan of the cow and herd economy. Clinical problems extend from the time of pregnancy diagnosis to pregnancy loss, abortion or parturition. Early pregnancy loss or abortion of multiple pregnancies lead in most cases to culling. In cows reaching their term, mean productive lifespan is up to about 300 days shorter for cows delivering twins than for cows delivering singletons. While there is an urgent need to address multiple pregnancy prevention procedures in the foreseeable future, the incidence of twin pregnancies continues to rise in parallel with increased milk production. Herein, we review two contrasting measures proposed for the time of twin pregnancy diagnosis: (1) gonadotropin-releasing hormone treatment for pregnancy maintenance, or (2) embryo reduction. These options are discussed in terms of their implications for individual animal health and herd economy. Our main conclusions find that manual twin reduction has proven to be the best management option, whereas the use of prostaglandin F_2α for inducing abortion may be a better option than doing nothing.