The influences of cycle stage and pregnancy upon cell glycosylation in the endometrium of the mare

Evidence of glycan mosaicism in the equine oviduct

We report a lectin histochemical study of oviductal ampulla and isthmus of thirteen mares euthanised at anestrus (1), estrus (5), 1-day post-ovulation (5) or diestrus (2). Staining with a panel of 5 lectins recognizing N-Acetylgalactosamine (GalNAc) residues revealed mosaicism in glycan expression in some specimens of ampulla and isthmus, peaking at estrus and 1-day post-ovulation (ov+1). In the ampulla, this presented as positively stained areas of both ciliated and non-ciliated cells in otherwise negatively-stained ampullae, ranging from small foci (diestrus) to areas up to 200 microns in length or more (estrus and ov+1). No positive clusters were observed in anestrus. In the isthmus, there was 1 specimen at estrus exhibiting discrete areas lacking stain with all five GalNAc-binding lectins which showed strong staining in the rest of the tissue, while at ov+1, another specimen showed unstained areas with 3 of the 5 GalNAc binding lectins. In both isthmus cases, terminal lactosamine (Gal-GlcNAc-) and α2-3-linked sialic acid were present in the unstained foci but were negligible elsewhere. Other glycans did not appear to be affected in this way. Various lectins and pre-treatment to cleave terminal sialic acid residues were used to assess how terminal glycosylation might differ between areas showing mosaicism and other epithelial cells in the respective tissue compartments. We suggest that one explanation for this mosaicism may be that it has resulted from absence or activation of a GalNAc transferase in clones of cells, most likely the blood group A-related enzyme UDP-GalNAc:Fuc α1-2 Gal α1-3GalNAc transferase. These glycosylation patterns may affect the adherence of sperm and/or zygotes to these sites, and more studies are required to evaluate the extent of its occurrence and functional significance.

The Dynamic Equine Embryo from Postfixation (Day 17) to the End of the Embryo Stage (Day 40)

After the cessation of equine embryo mobility (fixation) on mean Day 16, the embryonic vesicle is rotated or oriented so that the pole with the embryo proper is opposite to the mesometrial attachment. Orientation involves massage of the vesicle by contractions of the turgid uterine horn and greater thickening of the vesicle at the pole with the embryo proper. Thickening of the dorsal endometrium (encroachment) especially on each side of the mesometrial attachment accounts for a guitar-pick shape of the vesicle when viewed in cross section of the uterine horn. On Days 21-40, the allantoic sac expands, and the relative size of the yolk sac diminishes highlighted by carrying of the embryo proper to the dorsal aspect of the embryonic vesicle. There, the blood vessels from the embryonic vesicle meet at the mesometrial attachment to become the beginning of the umbilical cord. At the end of the embryo stage and beginning of the fetal stage (Day 40), the umbilical cord lengthens in association with the descent of the fetus to the bottom of the allantoic sac. After unilateral fixation of twins, a natural embryo reduction process frequently (∼85%) eliminates one of the embryos. The twins are massaged by the uterine contractions, and a critical proportion of the thicker wall of the doomed embryonic vesicle is forced into the thinner wall of the survivor. Natural embryo reduction does not occur for bilateral twins and reduction requires intervention from the theriogenologist.

Equine Embryo Mobility. A Friend of Theriogenologists

Equine embryo mobility and cessation of mobility (fixation) provide explanations to several enigmas in reproductive biology of the pregnant mare and provide an efficient solution to the twinning problem, the bane of brood-mare owners. Embryo mobility is maximum on Days 12 to 15 (Day 0 = ovulation) while the spherical embryo is growing from 9 to 23 mm in diameter. During mobility, the embryo can be anywhere in the uterine lumen regardless of side of ovulation. Mobility solved the enigmas of how a small embryo can block luteolysis in a relatively massive uterus and why the side of ovulation does not determine the side of the initial placental attachment. Fixation occurs on ∼ Day 16 at a bend or flexure in a uterine horn that has a cross sectional diameter of the endometrium that is similar to diameter of the embryo. The occurrence of fixation in the horn with smaller diameter solved several enigmas involving side of fixation such as (1) greater frequency of postpartum fixation in the formerly nongravid horn and (2) later fixation in a horse than in a pony; horses and ponies have a similar embryo diameter but horses have a larger uterus. Unilateral fixation of twins is associated with a high frequency (e.g., 85%) of natural embryo reduction (elimination of one member of a twin set) whereas bilateral fixation precludes natural embryo reduction. The theriogenologist can efficiently solve the twinning problem by compressing one mobile or bilaterally fixed embryo with finger/thumb or with the ultrasound probe.

Equine embryo mobility. A game changer

The equine embryo or embryonic vesicle on Days 11-15 postovulation travels with profound physiologic purpose throughout the lumen of the two uterine horns and uterine body making 12 to 22 trips between the two uterine horns per day. This phenomenon is termed embryo mobility and is unique in equids among domestic species. Apparently, the embryo first reaches the uterine body on Days 8 or 9. Mobility increases to maximum by Days 11 or 12 and continues until an abrupt cessation of mobility (fixation) on Days 15 (ponies) or 16 (horses and donkeys). The embryo is propelled by uterine contractions in response to the production of apparently both PGF2α and PGE2 by both the embryo and uterus. An increase in endometrial vascular perfusion accompanies the mobile embryo as it moves from horn to horn. Restricting the embryo to one uterine horn by a ligature has indicated that specific roles of the traveling embryo include the stimulation of uterine contractions, tone, vascularity, and edema and to curtail the production of the luteolysin (PGF2α) by the uterus. The increase in uterine tone, decrease in diameter of the uterine horns, and a flexure in the caudal portion of each horn collaborate in the selection of a horn of fixation. Embryo mobility is a game changer that has solved several long-time enigmas in mare reproduction and has provided a needed and effective finger/thumb compression method for eliminating one member of a twin set.

Hormonal Levels and Follicular Dynamics in Relation to the Oestrous Cycle in Barb and Arabian Mares, Algeria

This current study is an effort to understand the hormonal and follicular growth in the Barb and Arabian mares during the oestrous cycle; as mares are unique creatures. A total of 53 mares with 97 oestrous cycles were studied. The mares with a mean age of 10.38 ± 4.55 were examined by ultrasonography every day during their breeding season (2017). Two blood samples from each mare (n = 24) were obtained for progesterone (P4), oestrogen (oestradiol-17 beta) and follicle-stimulating hormone (FSH) determinations. The data revealed that the duration of the oestrous cycle was between 19 to 22 days. The pre-ovulatory follicle grew (3.02 ± 1.04) millimetre per day. The rate of cycles exploited in the mare (Arabian versus Barb) for conception was significantly different (P < 0.001). The maximal diameter of the follicle was 50.00 millimetre. The serum progesterone levels (P < 0.01) in mares were significantly higher in the luteal phase than those recorded during the time of oestrous. However, the levels of oestradiol and for FSH did not significantly change during the oestrous cycle in the mares. Determining the association between the size of the follicle and the hormone profiles were the most reliable criterion in the prediction of ovulation.

Puncture of the Equine Embryonic Capsule and Its Repair In Vivo and In Vitro

Vitrification of embryos >300 µm in diameter requires puncture of the glycoprotein capsule, although the size of the hole compatible with embryo survival is unknown. Forty-five day-7 or -8 embryos were punctured using a 30-µm glass biopsy pipette mounted on a micromanipulator (n = 20) or manually with either an acupuncture needle (∼100-µm diameter -hole; n = 10) or a microneedle with a <1 µm tip to produce a ∼30-µm diameter hole (n = 15) before transferring to recipient mares; further 12 embryos were punctured with either the acupuncture needle or microneedle before being cultured in vitro for 48 hrs (n = 3 per puncture group) or transferred to recipient mares and recovered 48 hrs later (n = 3 per puncture group). No pregnancies resulted from the 10 embryos punctured with the acupuncture needle, whereas 15 of 20 (75%) and 10 of 15 (67%) punctured on the micromanipulator or manually with the microneedle resulted pregnancies. Neither acupunctured nor microneedle-punctured embryos repaired their capsules in vitro. The acupunctured embryos also failed to repair their capsule after 48 hrs in vivo and subsequent uterine flushing yielded numerous capsular vesicles. The microneedle-punctured embryos did repair their capsule in vivo. Puncture with the microneedle opens the way for development of a manual method to vitrify equine embryos.