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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. [ABSTRACT FROM AUTHOR]

It is not known whether the likelihood of pregnancy after transfer of cryopreserved equine in vitro produced (IVP) blastocysts is related to post-thaw morphological characteristics, or could be impacted by other factors such as embryo biopsy prior to cryopreservation. This study examined associations between post-thaw morphological appearance of equine IVP embryos, and biopsy prior to slow-freezing, on the likelihood of pregnancy. Biopsy of IVP blastocysts was performed by harvesting cells herniated through the intra-cytoplasmic sperm injection (ICSI)-derived hole in the zona pellucida (ZP). Morphological characteristics (shape, extent of presumptive trophectoderm layer, % extruded blastomeres, expansion and % herniated cells) of frozen-thawed, biopsied (n = 36) and non-biopsied (n = 444) IVP blastocysts were recorded prior to transfer, and pregnancy outcome was recorded. A binomial multivariate generalized linear model was used to identify factors influencing pregnancy outcome. The overall pregnancy rate was 73.3 %, but was significantly affected by the interval between ICSI and confirmation of blastocyst formation, with lower pregnancy rates for later developing embryos (p < 0.01). Furthermore likelihood of pregnancy was significantly influenced by the stallion used for ICSI (p < 0.01) and the biological mother (p = 0.02), although no single biological sire or dam could be identified as contributing significantly. The biopsy procedure per se did not compromise pregnancy outcome (p = 0.59). On the other hand, pregnancy was less likely (p = 0.02) for blastocysts with more than 10 % herniated cells post-thaw (39 %; n = 13) than for those with fewer than 10 % (69 %; n = 166) or no (77 %; n = 301) herniated cells. No other post-thaw morphological characteristic affected pregnancy outcome. In conclusion, the sporadic herniation of a large part of the embryo through the ICSI-derived hole in the ZP during thawing negatively influences pregnancy outcome., Competing Interests: Conflicts of interests The authors declare that there are no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Circulating anti-Müllerian hormone concentration (AMH) is positively correlated to the number of small growing follicles in the mare and may reflect ovarian function. Dynamics of AMH during immunocontraception have not previously been investigated. This study aimed to compare serum AMH in mares following treatment with native porcine zona pellucida (pZP), recombinant pZP3 and pZP4 (reZP) or gonadotrophin releasing hormone (GnRH) vaccines, and saline-treated controls. Stored sera collected during two previous studies examining ovarian activity in mares during zona pellucida (ZP) or GnRH immunocontraception were analysed for serum AMH. Data were compared among treatment groups using mixed-effects linear regression and one-way ANOVA with post hoc testing. Correlations between AMH and previously reported clinical variables were estimated using Spearman's rho. Mares immunized against GnRH showed variable but detectable AMH throughout successive breeding and non-breeding seasons that were not significantly different to unvaccinated control mares. Mares treated with pZP demonstrated marked, reversible suppression of AMH. Mares immunized using reZP showed an intermediate effect. In the ZP study, AMH was positively correlated to serum progesterone concentrations, mean ovarian volumes and antral follicle counts, whereas no correlations between AMH and serum progesterone concentrations, mean ovarian volumes, or the presence of one or more follicles ≥20 mm in diameter were detected in the GnRH study. In conclusion, marked suppression of AMH during pZP immunocontraception, but not during GnRH immunocontraception, suggested enhanced suppression of ovarian follicular development and, or follicular function during pZP immunocontraception. Serum AMH concentrations may provide a novel tool for the assessment of ovarian function during ZP-based immunocontraception., (Copyright © 2017 Elsevier Inc. All rights reserved.)