Horse embryo diameter is influenced by the embryonic age but not by the type of semen used to inseminate donor mares

A prospective study of the proteome of equine pre-implantation embryo

The present study was conducted to investigate the global proteome of 8-day-old equine blastocysts. Follicular dynamics of eight adult mares were monitored by ultrasonography and inseminated 24 h after the detection of a preovulatory follicle. Four expanded blastocysts were recovered, pooled, and subjected to protein extraction and mass spectrometry. Protein identification was conducted based on four database searches (PEAKS, Proteome Discoverer software, SearchGUI software, and PepExplorer). Enrichment analysis was performed using g:Profiler, Panther, and String platforms. After the elimination of identification redundancies among search tools (at three levels, based on identifiers, peptides, and cross-database mapping), 1977 proteins were reliably identified in the samples of equine embryos. Proteomic analysis unveiled robust metabolic activity in the 8-day equine embryo, highlighted by an abundance of proteins engaged in key metabolic pathways like the TCA cycle, ATP biosynthesis, and glycolysis. The prevalence of chaperones among highly abundant proteins suggests that regulation of protein folding, and degradation is a key process during embryo development. These findings pave the way for developing new strategies to improve equine embryo media and optimize in vitro fertilization techniques.

Successful vitrification of equine embryos >300 microns without puncture or aspiration

BACKGROUND

Equine embryos >300 μm require puncture before vitrification. Protocols that do not require pre-puncture would make vitrification easier and allow for its widespread use.

OBJECTIVES

To design a successful vitrification protocol for embryos >300 μm without puncture as a pre-treatment.

STUDY DESIGN

Experimental in vivo study.

METHODS

Thirty-eight embryos were divided into 3 groups (G1: ≤300 μm, n = 11; G2: >300-500 μm, n = 20; G3: >500 μm, n = 7). Embryos were vitrified using a human vitrification kit. Following a 15 min exposure to equilibration solution (ES; 7.5% DMSO +7.5% ethylene glycol [EG] in a base medium [BM] of M199 HEPES-buffered medium [H199] + hydroxypropyl cellulose + gentamycin), embryos were exposed for ≤90 s to a vitrification solution (15% DMSO +15% EG + 0.5 M trelahose in BM), loaded onto a Cryolock and plunged into LN2. Warming was undertaken by plunging the Cryolock tip into 1 mL of H199 + 20% FBS + pen/strep +1 M sucrose at 42°C for 1 min. The embryos were then moved to a 0.5 M sucrose solution for 4 min, then placed in Vigro Hold for 4 min prior to transfer to a recipient.

RESULTS

Pregnancy rates were 81.8% (9/11) for G1, 80% (16/20) for G2, and 0% (0/7) for G3. The largest embryo to survive was 480 μm.

MAIN LIMITATIONS

Limited numbers and only one pregnancy was followed to term.

CONCLUSIONS

Equine embryos ≤480 μm can be successfully vitrified using a protocol with a longer exposure time to the ES. This does not appear to have a negative effect on early embryonic development.

Mule embryos share identical morphological features to horse embryos

This study aimed to compare the morphometry of horse and mule embryos. The study's hypothesis was that the micronuclei and nuclear fragmentation indexes are higher in mule embryos than in horse embryos. Twenty-two mares were randomly assigned in a crossover design to receive semen from a horse and a donkey; thirteen horse and thirteen mule embryos were obtained. Embryos were recovered eight days post-ovulation and classified according to the stage of development and quality with a score from 1 (excellent) to 4 (degenerate). Embryos were stained with Hoechst33342, and images were acquired with a fluorescence microscope. Nuclei were categorized as compact, mitotic, or fragmented; the fragmented and mitotic indexes were calculated based on their proportion over the total amount of nuclei counted. Embryo size and nuclear morphometry were assessed through ImageJ. Data analyses were carried out with GraphPad using ANOVA and T-test; significance was set at P < 0.05. The number of positive flushes in cycles bred with donkey or stallion semen did not differ when compared per cycle or per ovulation (13 vs. 12) (P > 0.05). One set of twins was recovered from a mare bred to the stallion that had a double ovulation; a mule and horse embryos were both recovered from eight mares. There was no difference in size between mule and horse embryos (915.5 ± 288 μm vs. 575.8 ± 69.6 μm) (P > 0.05) size of the study. The mule embryos scored between grade 1 (n = 9) and grade 2 (n = 4); similarly, the horse embryos scored between grade 1 (n = 6) and grade 2 (n = 7). The evaluation of the nuclear morphometry revealed that horse and mule embryos have a similar number of compact nuclei per sector (148.7 ± 6.8 nuclei/sector in mule embryos vs. 156.5 ± 8.5 nuclei/sector in horse embryos) (P > 0.05); however, the number of mitotic nuclei tended to be higher in mule embryos (5.2 ± 0.82) than in horse embryos (3.3 ± 0.3) (P = 0.08). The fragmented nuclei index was similar between mule (0.25 ± 0.1%) and horse (0.22 ± 0.1%) embryos (P = 0.4); the mitotic nuclei index was higher in mule embryos (3.2 ± 0.4%) than in horse embryos (2.2 ± 0.2%) (P = 0.02). In conclusion, embryo morphology of mares bred to a donkey and a horse shares similar nuclear ultrastructure features, except that mule embryos have a higher mitotic index.

Dynamic regulation of the transcriptome and proteome of the equine embryo during maternal recognition of pregnancy

During initial maternal recognition of pregnancy (MRP), the equine embryo displays a series of unique events characterized by rapid blastocyst expansion, secretion of a diverse array of molecules, and transuterine migration to interact with the uterine surface. Up to date, the intricate transcriptome and proteome changes of the embryo underlying these events have not been critically studied in horses. Thus, the objective of this study was to perform an integrative transcriptomic (including mRNA, miRNAs, and other small non-coding RNAs) and proteomic analysis of embryos collected from days 10 to 13 of gestation. The results revealed dynamic transcriptome profiles with a total of 1311 differentially expressed genes, including 18 microRNAs (miRNAs). Two main profiles for mRNAs and miRNAs were identified, one with higher expression in embryos ≤5 mm and the second with higher expression in embryos ≥7 mm. At the protein level, similar results were obtained, with 259 differentially abundant proteins between small and large embryos. Overall, the findings demonstrated fine-tuned transcriptomic and proteomic regulations in the developing embryo associated with embryo growth. The identification of specific regulation of mRNAs, proteins, and miRNAs on days 12 and 13 of gestation suggested these molecules as pivotal for embryo development and as involved in MRP, and in establishment of pregnancy in general. In addition, the results revealed new insights into prostaglandin synthesis by the equine embryo, miRNAs and genes potentially involved in modulation of the maternal immune response, regulation of endometrial receptivity and of late implantation in the mare.

A practical guide to estimate the age of the early CL by ultrasonography in mares examined for the first time to be used as recipients in a commercial embryo transfer program

The echogenicity of the early CL undergoes obvious changes during the first 5 days of luteal development. This phenomenon could potentially be used to estimate the age of the CL in mares which have not been checked frequently for the diagnosis of ovulation. The objective of this retrospective study was to determine the accuracy of estimating the age of the early CL (Day 0 to Day 4; Day 0 = Day of ovulation) in recipient mares examined for the first time in the breeding season to be used in a commercial embryo transfer (ET) program. The post-transfer pregnancy rate and embryo loss of 28 recipient mares whose CL age was estimated at the first scan of the breeding season (at least 2 months gap from the previous examination) were compared to that of 41 recipients in which the Day of ovulation had been determined by daily examinations and that received an embryo on the respective day. There was no difference (P > 0.1) in pregnancy (85.7 and 85.3%) or early embryonic loss (12.5% and 11.4%) between groups, respectively.

Effect of Timing of Postovulatory Insemination Relative to Human Chorionic Gonadotropin/Buserelin Treatment With 1 Straw of Frozen-Thawed Semen on Mare Fertility

The reproductive management of mares for frozen semen artificial insemination (AI) can be costly and labor intensive. Predicting the exact time of ovulation can be challenging even when ovulation-inducing drugs are used. The main objective of this retrospective study was to determine whether there was an effect of interval between examinations to detect ovulation on likelihood of pregnancy and early embryonic loss in mares after postovulatory breeding with a single straw of frozen/thawed semen. The second objective was to determine the efficacy of two different drugs (human chorionic gonadotropin vs. buserelin) for timely induction of ovulation. The length of the interval from penultimate check to ovulation had no significant effect on pregnancy or embryo loss rates (4 hours: 34.1% and 13.3% vs. 8 hours: 26.1% and 0% and 16 hours: 34.5% and 10%, respectively) nor did the ovulation-inducing drug used, number of the cycle, or the stallion. In conclusion, there appears to be no advantage of checking mares for ovulation during the late evening and night hours when using a postovulatory AI protocol and ovulation-inducing drugs.