13 In vitro and in vivo embryo production during foal heat in a mare: A case report

Abstract

The objective of this case report is to describe in vitro and in vivo embryo production during foal heat in a mare. A 16-year-old American Quarter Horse mare was presented for breeding and nonsurgical embryo recovery days post-foaling. Upon transrectal ultrasonographic examination, the donor mare was determined to be in oestrous (foal heat) with presence of moderate uterine oedema, a relaxed cervix, absence of uterine fluid, a 35-mm dominant follicle, and multiple (n = 7) subordinate follicles (10-20 mm). To increase embryo production, oocytes were retrieved by ultrasound-guided ovum pickup of all subordinate follicles. Upon collection, oocytes (n = 4) were placed in embryo holding medium for 18 h at room temperature (22°C) and then matured in equine maturation medium (EqMat, Campos-Chillon et al. 2019 J. Equine Vet. Sci. 73, 51-55) for 30 h at 38.5°C in 6% CO₂, 5% O₂, and 89% N₂. Matured oocytes (n = 3), as assessed by extrusion of the first polar body, underwent intracytoplasmic sperm injection with frozen-thawed semen and a Piezo-driven injection system. Injected oocytes were cultured in SCF1 (Owen et al. 2017 Reprod. Fertil. Dev. 29, 129-130) for 5 days and Dulbecco's modified Eagle medium/F12 plus 5% FBS for 2 days at 38.5°C in 6% CO₂, 5% O₂, and 89% N₂. On Day 10 post-foaling, the dominant follicle was 45 mm and the donor mare was inseminated with fresh semen (500 × 10⁶ progressively motile spermatozoa) and ovulation was induced with 1.8 mg of deslorelin IM (SucroMate, Thorn BioScience LLC). The donor mare ovulated within normal limits by 48 h post-induction of ovulation (12 days post-foaling) and embryo recovery was attempted 8 days post-ovulation (20 days post-foaling). The donor mare was then administered 250 μg of Cloprostenol IM (Estrumate, Merck Animal Health) to induce oestrus and was inseminated again with cooled semen (1 × 10⁹ progressively motile spermatozoa) for two consecutive cycles. Maturation, cleavage, and blastocyst rates were 57% (4/7), 67% (2/3), and 33% (1/3), respectively. The nonsurgical embryo recovery resulted in one expanded blastocyst grade 1. Both in vitro- and in vivo-produced blastocysts were transferred into synchronized recipients 5 days after oestrus on Day 16 and 20 post-foaling respectively. The donor mare got pregnant after the second cycle post-embryo recovery attempt. Pregnancy status of recipients and donor mare were evaluated at 14, 21, 30, and 50 days after embryo transfers or insemination with normal development for the three pregnancies. In conclusion, to our knowledge, this is the first case report describing in vitro and in vivo embryo production performed during foal heat increasing number of pregnancies in a post-foaling mare in a single cycle.