Morphokinetics of early equine embryo development in vitro using time-lapse imaging, and use in selecting blastocysts for transfer

Abstract

The use of time-lapse imaging (TLI) in the evaluation of morphokinetics associated with invitro developmental competence is well described for human, cattle and pig embryos. It is generally accepted that embryos that complete early cleavage sooner are more likely to form blastocysts and that timing of later events, such as blastocyst formation and expansion, are predictive of implantation potential and euploid status. In the horse, morphokinetics as a predictor of developmental competence has received little attention. In this study we evaluated the morphokinetics of early equine embryo development invitro for 144 oocytes after intracytoplasmic sperm injection and report the timings of blastocyst development associated with ongoing pregnancy for the first time. There was a tendency for time of cytoplasmic extrusion and first cleavage to occur earlier in the embryos that went on to form blastocysts (n=19) compared with those that arrested, and for first cleavage to occur earlier in blastocysts that established pregnancies that were ongoing (n=4) compared with pregnancies that were lost (n=2). TLI was clinically useful in identifying blastocysts when evaluation of morphology on static imaging was equivocal.

The Mare: A Pertinent Model for Human Assisted Reproductive Technologies?

“…In humans, in recent years, many tools have been developed to assist medical teams in this selection, while in horses, the quality assessment of cultured embryos is at its beginning. Methods can be invasive, such as embryo biopsy for pre-implantation genetic testing [ 124 , 157 , 158 ], or non-invasive, such as embryo monitoring by time-lapse imaging [ 159 , 160 , 161 , 162 , 163 ], metabolomics, or aneuploidy diagnosis on spent culture media (niPGT–A) [ 164 ]. These different techniques present different sensitivities, specificities, and acceptability, but have allowed to better control early embryonic development, to refine the criteria for the choice of the embryo to be transferred, and to promote single embryo transfer and thus considerably reduce the risks of multiple pregnancies (see below).…”

Morphokinetics of Porcine and Bovine Embryos and Anomalies in Their Development

“…There is abundance of data on embryo developmental kinetics in human [5,6,11,12,[19][20][21][22][23][24], although much less for cattle [10,[25][26][27][28] and some other species such as hamsters [29,30], mice [31][32][33][34] and horses [35]. The precise timing of morphokinetic events of in vitro produced porcine embryos has not yet been fully established.…”

Glucose concentration during equine in vitro maturation alters mitochondrial function

“…Images of each presumptive zygote were captured at 5-min intervals using the Primovision Time-Lapse System. Morphologic and morphokinetic analysis was performed on the resulting videos as previously described (Lewis et al 2019). Briefly, zona pellucida thickness and oocyte diameter were measured on the first frame by taking the mean of at least two measurements of each.…”

“…Time of cytoplasmic extrusion, first cleavage, and blastocyst formation was recorded for each injected oocyte when visualisation allowed, and this was complicated by the dark, opaque nature of the horse oocyte/embryo cytoplasm and movement due to remaining cumulus cells. Cytoplasmic extrusion, a phenomenon that appears to be physiological in the horse zygote and associated with competence for blastocyst development (Salgado et al 2018, Lewis et al 2019, was defined as the time cytoplasmic contents were first actively extruded from the oolemma. Time of first cleavage was defined as the time that the first visually identifiable indentation of the oolemma occurred, before a visualized cleavage.…”

“…Given the emerging evidence that nutrient provision during the periconceptual period can influence the lifelong health of the offspring (Watkins et al 2008, Fleming et al 2018, the aim of the present study was to compare the effect of the two commonly used glucose concentrations (5.6 mM and 17 mM) during IVM on equine COC energy metabolism. In addition, we evaluated the effects of these glucose concentrations during IVM on meiotic competence and developmental kinetics after ICSI, using our previously established methods (Lewis et al 2019). We also examined the effects of the IVM environment on oocyte and cumulus cell gene expression, measuring the expression of genes coding for components of key metabolic pathways known to be affected by hyperglycaemia in other species (Colton et al 2003, Chang et al 2005, Ratchford et al 2008, Wang et al 2010.…”