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

De novo reconstruction of a functional in vivo-like equine endometrium using collagen-based tissue engineering

To better understand molecular aspects of equine endometrial function, there is a need for advanced in vitro culture systems that more closely imitate the intricate 3-dimensional (3D) in vivo endometrial structure than current techniques. However, development of a 3D in vitro model of this complex tissue is challenging. This study aimed to develop an in vitro 3D endometrial tissue (3D-ET) with an epithelial cell phenotype optimized by treatment with a Rho-associated protein kinase (ROCK) inhibitor. Equine endometrial epithelial (eECs) and mesenchymal stromal (eMSCs) cells were isolated separately, and eECs cultured in various concentrations of Rock inhibitor (0, 5, 10 µmol) in epithelial medium (EC-medium) containing 10% knock-out serum replacement (KSR). The optimal concentration of Rock inhibitor for enhancing eEC proliferation and viability was 10 µM. However, 10 µM Rock inhibitor in the 10% KSR EC-medium was able to maintain mucin1 (Muc1) gene expression for only a short period. In contrast, fetal bovine serum (FBS) was able to maintain Muc1 gene expression for longer culture durations. An in vitro 3D-ET was successfully constructed using a collagen-based scaffold to support the eECs and eMSCs. The 3D-ET closely mimicked in vivo endometrium by displaying gland-like eEC-derived structures positive for the endometrial gland marker, Fork headbox A2 (FOXA2), and by mimicking the 3D morphology of the stromal compartment. In addition, the 3D-ET expressed the secretory protein MUC1 on its glandular epithelial surface and responded to LPS challenge by upregulating the expression of the interleukin-6 (IL6) and prostaglandin F synthase (PGFS) genes (P < 0.01), along with an increase in their secretory products, IL-6 (P < 0.01) and prostaglandin F2alpha (PGF2α) (P < 0.001) respectively. In the future, this culture system can be used to study both normal physiology and pathological processes of the equine endometrium.

Follicular metabolic alterations are associated with obesity in mares and can be mitigated by dietary supplementation

Obesity is a growing concern in human and equine populations, predisposing to metabolic pathologies and reproductive disturbances. Cellular lipid accumulation and mitochondrial dysfunction play an important role in the pathologic consequences of obesity, which may be mitigated by dietary interventions targeting these processes. We hypothesized that obesity in the mare promotes follicular lipid accumulation and altered mitochondrial function of oocytes and granulosa cells, potentially contributing to impaired fertility in this population. We also predicted that these effects could be mitigated by dietary supplementation with a combination of targeted nutrients to improve follicular cell metabolism. Twenty mares were grouped as: Normal Weight [NW, n = 6, body condition score (BCS) 5.7 ± 0.3], Obese (OB, n = 7, BCS 7.7 ± 0.2), and Obese Diet Supplemented (OBD, n = 7, BCS 7.7 ± 0.2), and fed specific feed regimens for ≥ 6 weeks before sampling. Granulosa cells, follicular fluid, and cumulus-oocyte complexes were collected from follicles ≥ 35 mm during estrus and after induction of maturation. Obesity promoted several mitochondrial metabolic disturbances in granulosa cells, reduced L-carnitine availability in the follicle, promoted lipid accumulation in cumulus cells and oocytes, and increased basal oocyte metabolism. Diet supplementation of a complex nutrient mixture mitigated most of the metabolic changes in the follicles of obese mares, resulting in parameters similar to NW mares. In conclusion, obesity disturbs the equine ovarian follicle by promoting lipid accumulation and altering mitochondrial function. These effects may be partially mitigated with targeted nutritional intervention, thereby potentially improving fertility outcomes in the obese female.

Recent advances of oocyte/embryo vitrification in mammals from rodents and large animals

Vitrification is a valuable technology that enables semipermanent preservation and long-distance or international transportation of genetically modified and native animals. In laboratory mice, vitrification maintains and transports embryos, and many institutions and companies sell vitrified embryos. In contrast, despite numerous papers reporting on vitrification in livestock over the past decade, practical implementation has yet to be achieved. However, with advances in genome editing technology, it is anticipated that the number of genetically modified domestic animals will increase, leading to a rise in demand for vitrification of oocytes and embryos. Here, we provide an objective overview of recent advancements in vitrification technology for livestock, drawing a comparison with the current developments in laboratory animals. Additionally, we explore the future prospects for vitrification in livestock, focusing on its potential benefits and drawbacks.

Ethanol, Carnoy, and paraformaldehyde as fixative solutions for histological evaluation of preantral follicles in equine ovarian tissue

The most adequate fixative solution for equine ovarian tissue is still to be determined as a tool to evaluate the improvement of methodological studies in assisted reproductive techniques and fertility preservation. This study aimed to evaluate a short-time ethanol 70% (ST-EtOH, 45 min) exposure as an alternative fixative compared with two classically fixatives [Carnoy's (CAR) solution and paraformaldehyde 4% (PFA)] at different fixation times (6 h, 12 h). The end points evaluated were morphology and classes of preantral follicles, follicular and stromal cell densities, and follicular and oocyte nuclear diameters in equine ovarian tissue. Ovaries (n = 6) from ovariectomized young mares were fragmented (3 × 3 × 1 mm; 20 fragments/ovary) and fixed in the tested treatments. Overall, a total of 11,661 preantral follicles were evaluated in 1444 histological slides. The ST-EtOH similarly preserved the preantral follicle morphometry and stromal cell density compared to the PFA fixative, regardless of the exposure time. Nonetheless, the CAR fixative solution had the greatest percentage of normal preantral follicles and the highest stromal cell density among all treatments. In conclusion, Carnoy's solution must be preferred compared with ST-EtOH and PFA fixatives for studies concerning the cellular morphology of equine ovarian tissue. Moreover, ST-EtOH fixative is a good alternative for equine ovarian tissue when a quick histological evaluation is required instead of more time-consuming and expensive techniques. Additional studies concerning the impact of different fixatives on the ultrastructure of cellular populations and their compatibility with IHC and molecular techniques in equine ovarian tissue are warranted.

Relationship Between Ovulation and Body Temperature in the Mare: A Preliminary Study

In the equine industry, monitoring of the reproduction cycle is key to be able to produce one foal per mare and per year. Ovulation detection is difficult partly due to the variability of the estrus length. Currently, the most reliable method for ovulation detection is transrectal ultrasonography. This technique, however, implies handling of the mare as well as veterinary costs. The aim of this experimentation is to study body temperature variations around ovulation. Nine reproduction cycles were monitored around ovulation. Transrectal ultrasonographies were performed each day as well as blood sampling to dose estradiol-17β and progesterone to confirm ultrasonographic results. Body temperature was automatically recorded every 10 minutes using an identification chip equipped with a temperature sensor implanted in the mares' neckline. Data were analyzed using linear mixed models. Daily body temperature pattern did not vary between the phases of the reproductive cycle (follicular, ovulatory and luteal). Temperature differences between phases, however, were identified and appeared hourly-specific. There was an increase of temperature at ovulation compared to the end of the follicular phase ranging from 0.51°C ± 0.21°C to 0.92°C ± 0.26°C and occurring between 04:30 and 08:00. Moreover, a significant increase of body temperature was measured during the first days of luteal phase, ranging from 0.29°C ± 0.17°C to 0.60°C ± 0.16°C, between 10:30 and 16:00. Body temperature varied around ovulation and it might be a promising tool for mare reproduction monitoring. A more complete study, however, focusing on the whole cycle is required.

The mammalian preimplantation embryo: Its role in the environmental programming of postnatal health and performance

During formation of the preimplantation embryo several cellular and molecular milestones take place, making the few cells forming the early embryo vulnerable to environmental stressors than can impair epigenetic reprogramming and controls of gene expression. Although these molecular alterations can result in embryonic death, a significant developmental plasticity is present in the preimplantation embryo that promotes full-term pregnancy. Prenatal epigenetic modifications are inherited during mitosis and can perpetuate specific phenotypes during early postnatal development and adulthood. As such, the preimplantation phase is a developmental window where developmental programming can take place in response to the embryonic microenvironment present in vivo or in vitro. In this review, the relevance of the preimplantation embryo as a developmental stage where offspring health and performance can be programmed is discussed, with emphasis on malnutrition and assisted reproductive technologies; two major environmental insults with important implications for livestock production and human reproductive medicine.

Embryonic resorption rates at canine pregnancy diagnoses: A retrospective evaluation

Pregnancy diagnosis in canines is generally performed during embryonic phase, between 19 and 35 days of gestation. At this stage embryonic resorptions can be observed, which, according to the literature, affects 11-26% of conceptuses and 5-43% of pregnancies. Resorption has been hypothesized as a physiological event in uterine overcrowding, however other factors may be involved, such as infectious or non-infectious diseases. This study aimed to retrospectively evaluate the incidence of embryo resorption at ultrasonographic pregnancy diagnosis in different dog breeds, and to identify the main factors determining the occurrence of the resorption sites. 95 pregnancy diagnoses were performed 21-30 days post-ovulation by ultrasound examination on 74 different animals. Breed, weight, and age of the bitches were recorded, and the reproductive anamnesis was collected from their medical records. The overall pregnancy rate was 91.6%. In 48.3% of pregnancies (42/87), at least one resorption site was visible, and embryonic resorption rate was 14.2% (61 resorption sites/431 total structures). Binary logistic regression showed a significant effect of age (P < 0.001), but not the size of the litter (P = 0.357), nor the size of the mother (P = 0.281) or any previous reproductive problems (P = 0.077). Age was significantly higher in pregnancies with resorptions than in normal ones (60.88 ± 18.24 and 40.27 ± 15.74 months, respectively, P < 0.001). The embryonic resorption rate was in line with previous findings, while the incidence of affected pregnancies was higher. Although resorptions may occur physiologically in pregnancies with large litters, a relationship between embryo resorption and litter size was not identified in our sample group, while aging increased the resorption rates. This, together with the occurrence of repeated embryonic resorptions in some bitches included in the study, suggests how resorptions could also be the result of pathological events. The underlying mechanisms and other factors that may be involved need further clarification.

Seasonal Variation of Melatonin Concentration and mRNA Expression of Melatonin-Related Genes in Developing Ovarian Follicles of Mares Kept under Natural Photoperiods in the Southern Hemisphere

This study investigated the seasonal variations in mRNA expression of FSH (Fshr), LH (Lhr) receptors, melatonin (Mt1 and Mt2) receptors, melatonin-synthetizing enzymes (Asmt and Aanat) and melatonin concentration in developing follicles from mares raised in natural photoperiods. For one year, ultrasonographic follicular aspiration procedures were performed monthly, and small (<20 mm), medium (20 to 35 mm) and large (>35 mm) follicles were recovered from five mares. One day before monthly sample collections, an exploratory ultrasonography conducted to record the number and the size of all follicles larger than 15 mm. The total number of large follicles were higher during the spring/summer (8.2 ± 1.9) than during autumn/winter (3.0 ± 0.5). Compared to autumn/winter seasons, there was an increase of Fshr and Aanat mRNA expressions in small, medium and large follicles, an increase of Lhr and Asmt mRNA expressions in medium and large follicles and an increase of Mt1 and Mt2 mRNA expressions in small and large follicles during spring/summer. The melatonin levels in follicular fluid were also higher during the spring/summer seasons. The present data show that melatonin locally upregulates the mRNA expression of Mt1 and Mt2 receptors and melatonin-forming enzymes in mare developing follicles during reproductive seasons.

Characterization of preantral follicle clustering and neighborhood patterns in the equine ovary

Understanding the transition from quiescent primordial follicles to activated primary follicles is vital for characterizing ovarian folliculogenesis and improving assisted reproductive techniques. To date, no study has investigated preantral follicle crowding in the ovaries of livestock or characterized these crowds according to follicular morphology and ovarian location (portions and regions) in any species. Therefore, the present study aimed to assess the crowding (clustering and neighborhood) patterns of preantral follicles in the equine ovary according to mare age, follicular morphology and developmental stage, and spatial location in the ovary. Ovaries from mares (n = 8) were collected at an abattoir and processed histologically for evaluation of follicular clustering using the Morisita Index and follicular neighborhoods in ovarian sections. Young mares were found to have a large number of preantral follicles with neighbors (n = 2,626), while old mares had a small number (n = 305). Moreover, young mares had a higher number of neighbors per follicle (2.6 ± 0.0) than old mares (1.2 ± 0.1). Follicle clustering was shown to be present in all areas of the ovary, with young mares having more clustering overall than old mares and a tendency for higher clustering in the ventral region when ages were combined. Furthermore, follicles with neighbors were more likely to be morphologically normal (76.5 ± 6.5%) than abnormal (23.5 ± 6.5%). Additionally, morphologically normal activated follicles had increased odds of having neighbors than normal resting follicles, and these normal activated follicles had more neighbors (2.6 ± 0.1) than normal resting follicles (2.3 ± 0.1 neighbors). In the present study, it was demonstrated that preantral follicles do crowd in the mare ovary and that clustering/neighborhood patterns are dynamic and differ depending on mare age, follicular morphology, and follicular developmental stage.

Granulosa Cells Improved Mare Oocyte Cytoplasmic Maturation by Providing Collagens

Assisted reproductive technology has important clinical applications and commercial values in the horse industry. However, this approach is limited largely by the low efficiency of oocyte in vitro maturation (IVM), especially cytoplasmic maturation. To improve the efficiency of mare oocyte IVM, we evaluated the effects of co-culture with cumulus–oocyte complexes (COCs) and granulosa cells (GCs) from follicles with small (&lt;15 mm) and large diameters (&gt;35 mm). Our results showed that oocyte nucleus maturation was not significantly improved by co-culturing with GCs. Interestingly, the cytoplasmic maturation of oocytes, defined by the distribution of cortical granules and mitochondria, as well as reactive oxygen species (ROS) levels, improved dramatically by co-culture with GCs, especially those derived from small follicles. Moreover, GCs promoted cumulus cell expansion by upregulating the expression of BMP15 in oocytes. To determine the mechanism underlying the effects of GCs, the transcriptomes of GCs from large and small follicles were compared. Expression levels of COL1A2, COL6A1, and COL6A2 were significantly higher in GCs from small follicles than in those from large follicles. These three genes were enriched in the extracellular matrix proteins-receptor interaction pathway and were involved in the regulation of collagens. Taken together, our results suggest that co-culture with GCs is beneficial to oocyte cytoplasmic maturation, and the increased expression of COL1A2, COL6A1, and COL6A2 improve the mare oocyte IVM system via the regulation of collagen.

Pregnancy and placental development in horses: an update

Horses have been domesticated by man and historical information mostly associates horses with men. Nowadays, however, horse riding is essentially by women. Women are also very much involved in equine sciences, with a large contribution to the understanding of fetoplacental development. While highlighting the work of female scientists, this review describes the recent advances in equine fetoplacental studies, focusing on data obtained by new generation sequencing and progress on the understanding of the role of placental progesterone metabolites throughout gestation. A second emphasis is made on fetal programming, a currently very active field, where the importance of maternal nutrition, mare management or the use of embryo technologies has been shown to induce long term effects in the offspring that might affect progeny's performance. Finally, new perspectives for the study of equine pregnancy are drawn, that will rely on new methodologies applied to molecular explorations and imaging.