Inflammation and fertility in the mare

Endometrial expression of antimicrobial peptides as markers of subclinical endometritis in mares

BACKGROUND

Endometritis is a major cause of subfertility in mares. Multiparous old mares are more susceptible to developing endometritis given that ageing is associated with an altered immune response and with inadequate physiological uterine clearance after breeding, which can lead to degenerative changes in the endometrium. Molecules such as antimicrobial peptides (AMPs) have been proposed as endometritis markers in the equine species.

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To investigate the endometrial expression of defensin-beta 4B (DEFB4B), lysozyme (LYZ) and secretory leukocyte peptidase inhibitor (SLPI) genes in mares either affected or not by subclinical endometritis, due to the role of these AMPs in the immune response to bacteria and inflammatory reactions.

METHODS

Endometrial biopsy for histopathological and gene expression examinations was performed on 26 mares. The inclusion criteria for the normal mare group (NM, N = 7) were 2-4 years of age, maiden status, no clinical signs of endometritis and a uterine biopsy score of I, while for mares affected by subclinical endometritis (EM, N = 19) the inclusion criteria were 10-22 years of age, barren status for 1-3 years, no clinical signs of endometritis and a uterine biopsy score between IIA and III.

RESULTS

A significantly higher expression of LYZ (NM: 0.76 [1.84-0.37] vs. EM: 2.78 [5.53-1.44], p = 0.0255) and DEFB4B (NM: 0.06 [0.11-0.01] vs. EM: 0.15 [0.99-0.08], p = 0.0457) genes was found in endometritis mares versus normal mares. Statistically significant moderate positive correlations were found between the level of expression of LYZ gene and both the age (r = 0.4071, p = 0.039) and the biopsy grade (r = 0.4831, p = 0.0124) of the mares.

MAIN LIMITATIONS

The study investigated a limited number of genes and mares, and the presence/location of the proteins coded by these genes was not confirmed within the endometrium by IHC.

CONCLUSIONS

If the results of this study are confirmed, LYZ and DEFB4B genes can be used as markers to identify mares that are affected by subclinical endometritis.

Isolation of lactic acid bacteria from the reproductive tract of mares as potentially beneficial strains to prevent equine endometritis

Endometritis, the inflammation of the endometrium, is the leading cause of subfertility in mares, and therefore responsible for major economic losses in the horse industry worldwide. It is generally treated with uterine lavages combined with ecbolic agents and local or systemic antibiotics. However, since antibiotic overuse has been associated with antimicrobial resistance in mares with persistent endometritis, new prevention and treatment alternatives are needed. One such alternative could be the use of probiotic lactic acid bacteria (LAB) isolated from the host. Thanks to their species specificity, resident microbiota may restore ecological equilibrium within the host, and therefore, help prevent infections and improve physiological functions. In the present study, 257 bacterial strains were isolated from 77 healthy mares, and 88.76% (n = 228) of them were phenotypically classified as LAB. Within this group, 65.79% were able to inhibit at least one strain from each of the genera that most commonly cause equine endometritis (Streptococcus equi subsp. zooepidemicus, Escherichia coli, and Staphylococcus spp.). Five strains (RCE11, RCE20, RCE91, RCE99, and RCE167) were selected on the basis of their beneficial properties: ability to autoaggregate and adhere to equine epithelial cells, high inhibition of and co-aggregation with all the bacteria isolated from clinical cases of endometritis evaluated, and negative co-inhibition between one another. All five were finally identified as Enterococcus spp., namely E. faecium (two strains), E. hirae (two strains), and E. gallinarum (one strain). Further studies will assess their safety and biotechnological potential for the design of a multi-strain probiotic formula to prevent equine endometritis.

General and comparative aspects of endometritis in domestic species: A review

Endometritis is a leading cause of sub- and infertility in domestic animal species. The healthy uterus is colonized by commensal bacteria, viruses and yeast/fungi that represent the nonpathogenic microbiota. A shift in the number or type of organisms accompanied by immune dysfunction, however, may trigger uterine infection and inflammation. Metritis is associated with inflammation of all uterine layers (endometrium, myometrium and perimetrium), whereas endometritis is a more superficial inflammation involving solely the endometrium. Endometritis generally occurs at two time points in domestic animal species, postpartum and postmating. Postpartum endometritis may chronically persist, either as a low-grade disease that often manifests as a vaginal discharge but not a systemic illness (in some species termed clinical endometritis) or sometimes subclinical where features are only detected by endometrial sampling. Contamination of the uterus at the time of mating occurs by direct deposition of semen (ejaculated or artificially inseminated) into the uterus. Improper drainage of the ejaculatory fluid or an inadequate immune response may result in persistent mating-induced endometritis. Both postpartum and postmating endometritis interferes with fertility by creating a suboptimal environment for embryo development and placentation, and chronic endometritis may have an impact on sperm survival and fertilization ability. In the postpartum animal, there may also be changes in milk production and maternal behaviour, which can affect offspring health and survival. Preventive strategies for endometritis largely depend on monitoring their known risk factors, which are sometimes specific with regard to the species. Effective, nonantibiotic therapy for endometritis is not available to date. Overall, extensive research has been performed in cattle and horses to unravel key aspects of endometritis, but in sows and bitches, the available literature is scant. Thus, the need and opportunity to investigate the condition vary considerably among domestic species and necessitate their comparative assessment. This article reviews general and comparative aspects of the diagnosis and classification, pathogenesis, preventive strategies and therapeutics of endometritis in domestic species with a specific focus on cows, mares, sows and bitches.

Construction of a model of endometritis in domestic rabbits using equine-derived pathogens and evaluation of therapeutic effect of sensitive drugs

Pathogenic bacteria were isolated from the uterine lavage fluid of a mare with endometritis. After identification and purification, the pathogenic bacteria were injected into the uterus of rabbits to induce endometritis. Then, anatomical, blood routine, chemical examination, and histopathological examinations were performed on the rabbits. Rabbit uterus was collected, and quantitative polymerase chain reaction (qPCR) was used to detect the mRNA expression of inflammatory factors including IL-1β, IL-6, and TNF-α in the rabbit uterus. In addition, enzyme-linked immunosorbent assay (ELISA) was used to detect the uterine concentrations of the inflammatory factors IL-1β, IL-6, and TNF-α. Western Blot was used to detect the protein expressions of NF-kB, IkBα, and TNF-α in the NF-kB pathway. An antibiotic treatment group was also set up to verify the accuracy of the results. The clinical examination results showed that there was a significant increase of leukocytes in the blood of the rabbits in the model group (P < 0.01). The uterus was congested, enlarged, and purulent. The integrity of the uterine lining was destroyed, and there was a significant increase of lymphocytes in the uterus (P < 0.01). The qPCR and ELISA results showed that the expressions of the inflammatory factors IL-1β, IL-6, and TNF-α in the uterus of rabbits were significantly increased (P < 0.01). Western blot results showed that the inflammatory factors IL-1β, IL-6, and TNF-α play a role in promoting inflammation through the NF-kB pathway. The results of the test provide a simple, economical, and reliable means of studying the occurrence, development, prevention, and treatment of equine endometritis.

Effects of Intra-Uterine Fluid Accumulation after Artificial Insemination on Luteal Function in Mares

After breeding or artificial insemination, especially with frozen/thawed semen, mares often develop a persistent uterine inflammation, which is diagnosed by intra-uterine fluid accumulation. Here, we explored whether intra-uterine fluid accumulation affects corpus luteum function and tested the hypothesis that intra-uterine fluid accumulation after artificial insemination alters blood flow in the corpus luteum and plasma progesterone concentrations. A total of 40 Standardbred mares were artificially inseminated with frozen-thawed semen 30 to 36 h after induction of ovulation, and cases with or without intra-uterine fluid accumulation were detected by ultrasound 12 h after insemination. Luteal blood flow was measured by Power Doppler ultrasonography 3 and 6 days after ovulation, progesterone concentration was measured in peripheral plasma by ELISA 6 days after ovulation, and pregnancy was diagnosed by ultrasonography 14 days after ovulation. Luteal blood flow increased between 3 and 6 days after ovulation, but blood flow did not differ significantly between cases with (n = 28) and without (n = 25) intra-uterine fluid accumulation after insemination. Surprisingly, progesterone concentrations were higher in cases of intra-uterine fluid accumulation than cases without (9.3 ± 1.1 vs. 6.6 ± 0.5 ng/mL, p = 0.048). Pregnancy was less likely in cases with intra-uterine fluid accumulation than in cases without (10/28 vs. 17/25, p = 0.019), and there was a negative correlation between the severity of intra-uterine fluid accumulation and per cycle pregnancy rate. These data suggest that although intra-uterine fluid accumulation increases the secretion of progesterone, pregnancy is more dependent on uterine health than ovarian function.

The NF-κB signaling pathway in mare's endometrium infiltrated with the inflammatory cells

Endometritis is an important issue decreasing mares' fertility. In the case of endometritis both, inflammatory cells infiltration and proinflammatory molecules production are regulated by various cellular and gene-regulatory mechanisms, including the nuclear factor-κB (NF-κB) dependent pathway. NF-κB signaling pathway has been recently studied in the equine endometrium in the context of endometrosis. Thus, this study aimed to determine gene transcription of NF-κB subunits (RelA; NF-κB1; NF-κB2), proinflammatory molecules (MCP-1; IL-6), and hyaluronan synthases (HAS 1; HAS 2; HAS 3) in endometritis and compare them with the intensity and type of inflammatory cell infiltration. Endometrial samples, collected post-mortem from cyclic mares in estrus or diestrus, were classified histologically and examined using quantitative PCR. Transcription NF-κB subunits genes did not differ with either inflammatory intensity or type of inflammatory cell infiltration. Transcription of MCP-1 and IL-6 genes increased with the severity of inflammation, with the involvement of HAS 3 and HAS 2 genes, as opposed to HAS 1 genes. These proinflammatory molecules and hyaluronan synthases in the equine inflamed endometrium do not seem to be regulated by the NF-κB pathway. Hence, separate signaling pathways for the development and progression of equine endometritis and endometrosis may be suggested.

Effect of platelet lysate on uterine response of mares susceptible to persistent mating-induced endometritis

Many mares are susceptible to persistent mating-induced endometritis (PMIE), an important cause of reduced fertility. Platelet lysate (PL) derives from freeze-thawing platelets after concentration, so that growth factors are released from the platelets. Among the advantages of PL compared to platelet-rich plasma (PRP), it can be frozen stored and allogenic use for PL might also be conceivable. Platelet-rich plasma beneficially reduced inflammatory response in PMIE mares when administered 24 h pre- or 4 h post-AI. The aim of this study was to test the effect of PL on inflammatory uterine response in mares susceptible to PMIE. A total of 14 mares susceptible to PMIE (based on presence of fluid or inflammatory cells 24 h after AI) underwent an untreated (Ctr) cycle followed by a treated (PL) cycle. From each mare, 100 mL of citrated whole blood was obtained for PRP production by centrifugation. The resultant PRP was brought to a final volume of 10 mL with platelet poor plasma and frozen at -80 °C to obtain PL. On untreated cycles, mares were inseminated with frozen-thawed semen 36 h after ovulation induction. On treated cycles, PL was thawed, infused into the uterus 12 h after ovulation induction, and AIs were performed 24 h later. The number of neutrophils in uterine cytology (score 1(normal)-3(severe inflammation)) evaluated by optical microscopy, uterine fluid accumulation (height x width) and uterine edema (score 0-3) observed in ultrasonography, were analysed. Pregnancy was evaluated by ultrasonography 14 days after ovulation. A significant decrease (P < 0.05) was observed on cytology score (PL 1.3 ± 0.1 vs Ctr 2.0 ± 0.1), fluid accumulation (PL 79.5 ± 30.1 mm² vs Ctr 342.7 ± 52.9 mm²) and edema score (PL 1.8 ± 0.2 vs Ctr 2.3 ± 0.2) in treated mares. Pregnancy rate in PL-treated cycles (3/12) and control cycles (2/14), were not significantly different (P > 0.05). According to the results, we conclude that treatment with PL in mares classified as susceptible to PMIE appears to reduce the inflammatory response after breeding, based on clinical signs of uterine edema, IUF accumulation and PMNs migration.

Inflammatory Markers in Uterine Lavage Fluids of Pregnant, Non-Pregnant, and Intrauterine Device Implanted Mares on Days 10 and 15 Post Ovulation

Simple Summary

While intrauterine devices (IUDs) are used to prevent disturbing oestrous behaviour in sport mares, their mechanism of action has not been elucidated. The presence of an embryo or an IUD prevents cyclooxygenase-2 (COX-2) and subsequently prostaglandin (PG) release and luteolysis. It has been suggested that a plastic sphere would mimic the embryo by mechanotransduction. However, there is some evidence that IUDs also cause endometrial inflammation, which might contribute to luteostasis. The aim of this study was to investigate the presence and time course of possible inflammation by evaluating changes in uterine fluid composition. On Day 10 after ovulation, events leading to COX-2 and prostaglandin F_2α (PGF_2α) inhibition start, whereas either luteolysis occurs or the corpus luteum is maintained on Day 15. Therefore, uterine lavage fluid was evaluated at two time points in inseminated mares, either pregnant or not, and in mares inserted with an IUD. On Day 10, PGF_2α concentration in the fluid was significantly lower in the IUD group than in the pregnant mare one but did not differ from the non-pregnant mare group. On Day 15, the IUD group had significantly higher levels of the modulatory cytokine IL-10 and inhibin A, which could indicate previous inflammation and resolution stage.

Abstract

Intrauterine devices (IUDs) are used in mares to suppress oestrous behaviour, but the underlying mechanism is yet to be elucidated. The presence of an embryo or an IUD prevents cyclooxygenase-2 (COX-2) and, subsequently, prostaglandin (PG) release and luteolysis. However, inflammation may also be involved. Endometrial inflammatory markers in uterine lavage fluid were measured on Day 10 (EXP 1, n = 25) and Day 15 (EXP 2, n = 27) after ovulation in inseminated mares, non-pregnant or pregnant, and in mares in which a small plastic sphere had been inserted into the uterus 4 (EXP 1) or 3 days (EXP 2) after ovulation. Uterine lavage fluid samples were analysed for nitric oxide (NO), prostaglandin E₂ (PGE₂) (only EXP 1), prostaglandin F_2α (PGF_2α), inhibin A and cytokines, and blood samples for progesterone and oestradiol. On Day 10, the concentration of PGF_2α was lower (p < 0.05) in the IUD group than in pregnant mares. The concentration of the modulatory cytokine IL-10 was significantly higher in the IUD group in comparison to non-pregnant mares, and inhibin A was significantly higher in IUD mares than in the pregnant counterparts on Day 15. The results suggest that the presence of IUD causes endometrial inflammation which is at a resolution stage on Day 15.

Identification of genes associated with susceptibility to persistent breeding-induced endometritis by RNA-sequencing of uterine cytobrush samples

This study aimed to investigate the susceptibility to persistent breeding-induced endometritis (PBIE). Cytobrush samples were collected from 81 broodmares 1-3 days before artificial insemination (AI). Susceptibility to PBIE was evaluated by the presence of ≥ 2 cm of intrauterine fluid 24 h after AI, besides the fertility was determined by a sonographic pregnancy diagnosis 2 weeks after ovulation. RNA expressions were compared between susceptible non-pregnant (SNP) mares (n=9) and resistant pregnant (RP) mares (n=9) as well as between susceptible pregnant (SP) mares (n=9) and susceptible non-pregnant (SNP) mares. 66 differentially expressed genes (DEGs) were identified between SNP and RP mares and 60 DEGs between SP and SNP mares. In SNP compared to RP mares, transcript levels of genes regulating steroid hormone metabolism and neutrophil chemotaxis were lower, while higher for genes participating in uterine inflammation.Transcripts of genes related to extracellular matrix degradation, tissue adhesions, and fibrosis were lower in SP mares than in SNP mares, while higher for genes related to uterine cell proliferation, differentiation, and angiogenesis in SP mares than SNP mares. In conclusion, increased transcript levels of apolipoprotein E (APOE) and roundabout 2 (ROBO2), cluster domain 44 (CD44), integrin beta 3 (ITGB3), and epidermal growth factor (EGF) are possible biomarkers for susceptibility to PBIE. While higher expression of fibroblast growth factor 9 (FGF9), kinase domain receptor (KDR), and C-X-C motif chemokine ligand (CXCL) 16, collagen type V alpha 2 (COL5A2) and fibronectin (FN1) are suggested indicators of fertility in susceptible mares if they receive proper breeding management.

Comparative study utilizing different post-breeding treatment regimens in cyclic Arabian mares

BACKGROUND AND AIM

Post-breeding treatment is the most common practice in the reproductive management of mares. Oxytocin, uterine lavage, and intrauterine (I/U) antibiotic are usually used as prophylactic therapy. This study aimed to determine the most efficient prophylactic treatment regimen among six treatment protocols applied during natural breeding of cyclic Arabian mares.

MATERIALS AND METHODS

The current study was conducted on cyclic Arabian mares that were subdivided into three age categories (n=968): Category I (5-10 years, n=380), Category II (11-15 years, n=361), and Category III (≥16 years, n=227). Six prophylactic treatments were applied after 4 h of breeding. According to the treatment regimen, treated mares (n=483) were divided into six treatment groups: A (n=80), treated with I/U antibiotic (1 g gentamicin); B (n=81), I/U lavage (normal saline 500 mL); C (n=83), intramuscular (I/M) oxytocin (10 IU); D (n=82), I/U antibiotic and I/M oxytocin; E (n=78), I/U lavage and I/M oxytocin; and F (n=79), I/U lavage with I/U antibiotic and I/M oxytocin. Non-treated mares were classified as controls (n=485). Ultrasonography was performed to monitor pregnant mares 30 and 60 days after mating, and mares were followed until foaling.

RESULTS

Pregnancy and foaling results reveals that in age Category I, treatment with oxytocin alone or oxytocin with I/U lavage showed the highest pregnancy and foaling rates (p<0.01). In age Category II, the highest pregnancy and foaling rates were observed in lavage treatment (p<0.01), whereas, in age Category III, the good pregnancy and foaling rates were monitored in treatment with oxytocin and I/U lavage (p<0.01).

CONCLUSION

Treatment with systemic I/M oxytocin is ideal in early age group mares (5-10 years of age). However, irrespective of the age categories, all mares exhibited high pregnancy and foaling rates after treatment with systemic I/M oxytocin and I/U lavage with normal saline (0.9%) 4 h post-breeding.

Antimicrobial Resistance in Equine Reproduction

Bacteria develop resistance to antibiotics following low-level "background" exposure to antimicrobial agents as well as from exposure at therapeutic levels during treatment for bacterial infections. In this review, we look specifically at antimicrobial resistance (AMR) in the equine reproductive tract and its possible origin, focusing particularly on antibiotics in semen extenders used in preparing semen doses for artificial insemination. Our review of the literature indicated that AMR in the equine uterus and vagina were reported worldwide in the last 20 years, in locations as diverse as Europe, India, and the United States. Bacteria colonizing the mucosa of the reproductive tract are transferred to semen during collection; further contamination of the semen may occur during processing, despite strict attention to hygiene at critical control points. These bacteria compete with spermatozoa for nutrients in the semen extender, producing metabolic byproducts and toxins that have a detrimental effect on sperm quality. Potential pathogens such as Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa may occasionally cause fertility issues in inseminated mares. Antibiotics are added during semen processing, according to legislation, to impede the growth of these microorganisms but may have a detrimental effect on sperm quality, depending on the antimicrobial agent and concentration used. However, this addition of antibiotics is counter to current recommendations on the prudent use of antibiotics, which recommend that antibiotics should be used only for therapeutic purposes and after establishing bacterial sensitivity. There is some evidence of resistance among bacteria found in semen samples. Potential alternatives to the addition of antibiotics are considered, especially physical removal separation of spermatozoa from bacteria. Suggestions for further research with colloid centrifugation are provided.

The Inhibitory Effect of Noscapine on the In Vitro Cathepsin G-Induced Collagen Expression in Equine Endometrium

Cathepsin G (CAT) is a protease released by neutrophils when forming neutrophil extracellular traps that was already associated with inducing type I collagen (COL1) in equine endometrium in vitro. Endometrosis is a fibrotic condition mainly characterized by COL1 deposition in the equine endometrium. The objective was to evaluate if noscapine (an alkaloid for cough treatment with anti-neoplastic and anti-fibrotic properties) would reduce COL1A2 transcription (evaluated by qPCR) and COL1 protein relative abundance (evaluated by western blot) induced by CAT in equine endometrial explants from follicular and mid-luteal phases treated for 24 or 48 h. The explants treated with CAT increased COL1 expression. Noscapine decreased COL1A2 transcription at both estrous cycle phases, but COL1 relative protein only at the follicular phase, both induced by CAT. Additionally, the noscapine anti-fibrotic action was found to be more effective in the follicular phase. The CAT treatment caused more fibrosis at the longest period of treatment, while noscapine acted better at the shortest time of treatment. Our results showed that noscapine could act as an anti-fibrotic drug in equine endometrosis by inhibiting CAT in vitro. Noscapine offers a new promising therapeutic tool for treating fibrosis as a single non-selective agent to be considered in the future.

Pharmacological activation of rev-erbα suppresses LPS-induced macrophage M1 polarization and prevents pregnancy loss

BACKGROUND

Circadian rhythm is an important player for reproduction. Rev-erbα, a significant clock gene, is involved in regulating cell differentiation, inflammation and metabolism. Macrophage polarization plays crucial roles in immune tolerance at the maternal-fetus interface, which also modulates the initiation and resolution of inflammation. Alteration of macrophage polarization induces adverse pregnancy outcomes such as infertility, recurrent spontaneous abortion and preterm labor.

RESULTS

Decidual macrophages from LPS-induced mice abortion model displayed M1-like bias, accompanied by decreased expression of Rev-erbα. SR9009, an agonist of Rev-erbα, may reduce lipopolysaccharide (LPS)-induced M1 polarization of macrophages via activation of PI3K but not NF-κB signaling pathway. Furthermore, SR9009 could reduce M1-like polarization of decidual macrophages induced by LPS and attenuate LPS-induced resorption rates in mice model.

CONCLUSIONS

Both in vivo and in vitro experiments demonstrated that the pharmacological activation of Rev-erbα using SR9009 could attenuate the effect of LPS on macrophage polarization and protect pregnancy. This study may provide a potential therapeutic strategy for miscarriage induced by inflammation.

A comparative analysis of the intrauterine transcriptome in fertile and subfertile mares using cytobrush sampling

Background

Subfertility is a major problem in modern horse breeding. Especially, mares without clinical signs of reproductive diseases, without known uterine pathogens and no evidence of inflammation but not becoming pregnant after several breeding attempts are challenging for veterinarians. To obtain new insights into the cause of these fertility problems and aiming at improving diagnosis of subfertile mares, a comparative analysis of the intrauterine transcriptome in subfertile and fertile mares was performed. Uterine cytobrush samples were collected during estrus from 57 mares without clinical signs of uterine diseases. RNA was extracted from the cytobrush samples and samples from 11 selected subfertile and 11 fertile mares were used for Illumina RNA-sequencing.

Results

The cytobrush sampling was a suitable technique to isolate enough RNA of high quality for transcriptome analysis. Comparing subfertile and fertile mares, 114 differentially expressed genes (FDR = 10%) were identified. Metascape enrichment analysis revealed that genes with lower mRNA levels in subfertile mares were related to ‘extracellular matrix (ECM)’, ‘ECM-receptor interaction’, ‘focal adhesion’, ‘immune response’ and ‘cytosolic calcium ion concentration’, while DEGs with higher levels in subfertile mares were enriched for ‘monocarboxyl acid transmembrane transport activity’ and ‘protein targeting’.

Conclusion

Our study revealed significant differences in the uterine transcriptome between fertile and subfertile mares and provides leads for potential uterine molecular biomarkers of subfertility in the mare.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07701-3.

Viral infection and allergy - What equine immune responses can tell us about disease severity and protection

Horses have many naturally occurring diseases that mimic similar conditions in humans. The ability to conduct environmentally controlled experiments and induced disease studies in a genetically diverse host makes the horse a valuable intermediate model between mouse studies and human clinical trials. This review highlights important similarities in the immune landscape between horses and humans using current research on two equine diseases as examples. First, equine herpesvirus type 1 (EHV-1) infection initiates a series of innate inflammatory signals at its mucosal entry site in the upper respiratory tract. These inflammatory markers are highly synchronized and predictable between individuals during viral respiratory infection and ultimately lead to adaptive immune induction and protection. The timing of early inflammatory signals, followed by specific adaptive immune markers correlating with immunity and protection, allow accurate outbreak tracking and also provide a foundation for understanding the importance of local mucosal immunity during other viral respiratory infections. Second, rare peripheral blood immune cells that promote allergic inflammation can be analyzed during Culicoides hypersensitivity, a naturally occurring type I IgE-mediated allergic disease of horses. Rare immune cells, such as IgE-binding monocytes or basophils, can be studied repeatedly in the horse model to unravel their larger mechanistic role in inflammation during allergic and other inflammatory diseases. We conclude with a survey of all other common equine inflammatory conditions. Together, this review serves as a reference and rationale for the horse as a non-rodent model for immunological research.

Seminal plasma, and not sperm, induces time and concentration-dependent neutrophil extracellular trap release in donkeys

BACKGROUND

In several mammalian species, acute endometritis driven by the recruitment of polymorphonuclear cells (PMN) occurs in response to semen. These PMNs release DNA to form neutrophil extracellular traps (NETs) in cattle, horse and human, leading to sperm entrapment. While there is no evidence of this phenomenon occurring in donkeys, artificial insemination (AI) with frozen-thawed semen, which results in very poor pregnancy rates, leads to a large PMN recruitment to the uterus.

OBJECTIVES

To investigate whether donkey semen can trigger NET release (NETosis) and if excessive NETosis occurs in response to frozen-thawed semen.

STUDY DESIGN

In vitro experiments.

METHODS

Jenny PMNs were exposed to jackass fresh or frozen-thawed semen, isolated sperm or seminal plasma (SP), over the course of three experiments. NET formation in response to different treatments was assessed through manual quantification of stained slides. A one-way analysis of variance (ANOVA), followed by a post hoc Sidak test, was carried out to determine statistical significance.

RESULTS

NET release occurred in a semen concentration- and incubation-time-dependent manner. Surprisingly, frozen-thawed donkey sperm did not increase NETosis rate in comparison with the control (23 ± 2.5% vs. 31 ± 3.7%; P > .05), whereas fresh semen exposure did (78 ± 5.7% vs. 26 ± 3.2%, P < .01). NETosis increased in the presence of SP, regardless of the presence or absence of sperm, in comparison with the control in both fresh (84 ± 5.2% and 77 ± 5.0% vs. 12 ± 2.7%, respectively; P < .01) and frozen (95 ± 2.2% and 94 ± 2.9% vs. 14 ± 3.8%, respectively; P < .01) samples. Moreover, exposure of PMN to viable and motile sperm, in the absence of SP, did not increase NETosis rates (P > .05).

CONCLUSIONS

Donkey SP, and not sperm-intrinsic factors, is able to trigger NETosis in both time- and semen concentration-dependent manner. The physiological relevance of such response against semen in the donkey remains to be elucidated.

Treatments for Endometritis in Mares Caused by Streptococcus equi Subspecies zooepidemicus: A Structured Literature Review

Bacterial infections are the main causes of endometritis in mares. It is well known that the most common bacterial pathogen is Streptococcus equi subspecies zooepidemicus (SEZ). This structured review was completed according to the PRISMA procedure to search endometritis treatment protocols published between 1990 and 2020 it was our intent to evaluate the actual effects of different treatment protocols for endometritis caused by SEZ. The trials included were collected from Pubmed, CAB and Agricola. Ten articles with 116 horses and 17 different interventions were identified. The results of this structured review indicated that the reported antibiotics, immunomodulatory agents and fresh white blood cell treatments were superior for treating SEZ caused endometritis in mares, whereas oxytocin and uterine lavage alone may not be as effective as presumed. The inclusion and evaluation of more randomized controlled trials may be helpful for further elucidation of the differences.

Intrauterine infusion of killed semen adversely affects uterine blood flow and endometrial gene expression of inflammatory cytokines in mares susceptible to persistent breeding-induced endometritis

Persistent breeding-induced endometritis (PBIE) is a leading cause of infertility in mares. The objective of the study was to assess genital perfusion and endometrial gene expression of inflammatory cytokines in mares classified as susceptible (n = 5) or resistant (n = 5) to PBIE. Ten mares were examined daily during estrus until 6 d after hCG-induced ovulation for two estrous cycles. Twenty-four hours after application of 1500 IU hCG, 4 mL of killed (by repeated freezing in liquid nitrogen and thawing at 50 °C) deep-frozen semen or sterile saline was instilled into the uterine body and examinations were carried out immediately before and 3, 6, and 12 h after intrauterine infusion. Examinations included blood sampling to determine plasma progesterone (P₄) concentrations, and transrectal ultrasonography in B- and color Doppler mode to determine follicular and luteal size and blood flow, the extent of intrauterine fluid, as well as time-averaged maximum velocity (TAMV), blood flow volume (BFV), and blood flow resistance (expressed as pulsatility index, PI) of the uterine arteries. Additionally, endometrial biopsies were obtained at 24 h before, and 2 and 7 d after infusion, and mRNA expressions of IL1B, IL6, IL8, IL10, TNF, CASP3, and COX2 were determined by qRT-PCR. Statistical analyses were performed with mixed models. Intrauterine fluid retention (diameter >20 mm for at least 3 d) was found after infusion of killed semen in five susceptible mares. There was no treatment effect (semen vs saline; P > 0.05) on genital blood flow, plasma P₄ concentration, and endometrial gene expression. In comparison to resistant mares, susceptible mares had an increased (P = 0.04) BFV of the uterine arteries at 24 h before intrauterine infusion of killed semen, and an increased (P = 0.03) PI at 2 d after infusion. The TAMV, plasma P₄ concentrations, and follicular and luteal size and blood flow did not differ (P > 0.05) between resistant and susceptible mares. Endometrial mRNA expression of IL1B increased (P = 0.05) at 2 d after the infusion of killed semen in the susceptible mares, and the expression of IL10 increased (P = 0.003) at 7 d after the infusion within the resistant mares. Interleukin 6 mRNA was increased (P = 0.05) in susceptible compared to resistant mares at 2 d after infusion. In summary, an intrauterine infusion of killed semen increases uterine blood flow resistance and alters endometrial gene expression of inflammatory cytokines for at least 7 d but does not affect ovarian blood supply and luteal function in mares susceptible to PBIE.

Baicalin attenuates endometritis in a rabbit model induced by infection with Escherichia coli and Staphylococcus aureus via NF-κB and JNK signaling pathways

In this study, a rabbit endometritis model was developed to study cow endometritis. In addition, the protective effects of baicalin (a flavonoid) against endometritis were investigated. Clinical symptoms, differential leukocyte counting, uterine secretion smear microscopy and chemical examination, urine testing, and signs of necropsy showed abnormal changes and inflammatory responses in the uterus of rabbits. Histopathological results revealed visible inflammatory exudates and blood spots between intercellular spaces which confirmed that the rabbit endometritis model was successfully developed. Most importantly, these inflammatory signs were partially attenuated with baicalin treatment. The data revealed that the increased body temperature and leukocyte cells, pus, and the detachment of epithelial cells were alleviated with baicalin administration in a dose-dependent manner. Histopathological tissue changes such as inflammatory cells infiltrates, hyperemia, hemorrhages, and shedding of epithelial cells were partially attenuated with baicalin treatment. In addition, the mRNA expression of inflammation-related genes (iNOS, IL-1β, TNF-α, IL-10, IL-4, and IL-6) was significantly altered in RAW264.7 cells after LPS treatment. Further, the phosphorylated protein expression of JNK, p65, and IκBα were significantly reduced with LPS treatment. Intriguingly, baicalin pretreatment reversed the alteration in mRNA expression of inflammation-related genes and significantly reduced the phosphorylation of JNK, p65, and IκBα. In summary, our results suggest that baicalin has protective effects on bacterial-induced endometritis in rabbits that involve the suppression of NF-κB and JNK signaling pathways and pro-inflammatory cytokines.

The functions of CAP superfamily proteins in mammalian fertility and disease

BACKGROUND

Members of the cysteine-rich secretory proteins (CRISPS), antigen 5 (Ag5) and pathogenesis-related 1 (Pr-1) (CAP) superfamily of proteins are found across the bacterial, fungal, plant and animal kingdoms. Although many CAP superfamily proteins remain poorly characterized, over the past decade evidence has accumulated, which provides insights into the functional roles of these proteins in various processes, including fertilization, immune defence and subversion, pathogen virulence, venom toxicology and cancer biology.

OBJECTIVE AND RATIONALE

The aim of this article is to summarize the current state of knowledge on CAP superfamily proteins in mammalian fertility, organismal homeostasis and disease pathogenesis.

SEARCH METHODS

The scientific literature search was undertaken via PubMed database on all articles published prior to November 2019. Search terms were based on following keywords: 'CAP superfamily', 'CRISP', 'Cysteine-rich secretory proteins', 'Antigen 5', 'Pathogenesis-related 1', 'male fertility', 'CAP and CTL domain containing', 'CRISPLD1', 'CRISPLD2', 'bacterial SCP', 'ion channel regulator', 'CatSper', 'PI15', 'PI16', 'CLEC', 'PRY proteins', 'ASP proteins', 'spermatogenesis', 'epididymal maturation', 'capacitation' and 'snake CRISP'. In addition to that, reference lists of primary and review article were reviewed for additional relevant publications.

OUTCOMES

In this review, we discuss the breadth of knowledge on CAP superfamily proteins with regards to their protein structure, biological functions and emerging significance in reproduction, health and disease. We discuss the evolution of CAP superfamily proteins from their otherwise unembellished prokaryotic predecessors into the multi-domain and neofunctionalized members found in eukaryotic organisms today. At least in part because of the rapid evolution of these proteins, many inconsistencies in nomenclature exist within the literature. As such, and in part through the use of a maximum likelihood phylogenetic analysis of the vertebrate CRISP subfamily, we have attempted to clarify this confusion, thus allowing for a comparison of orthologous protein function between species. This framework also allows the prediction of functional relevance between species based on sequence and structural conservation.

WIDER IMPLICATIONS

This review generates a picture of critical roles for CAP proteins in ion channel regulation, sterol and lipid binding and protease inhibition, and as ligands involved in the induction of multiple cellular processes.

Vaginal Microbiota Is Stable throughout the Estrous Cycle in Arabian Maress

Lactic acid bacteria (LAB) dominate human vaginal microbiota and inhibit pathogen proliferation. In other mammals, LAB do not dominate vaginal microbiota, however shifts of dominant microorganisms occur during ovarian cycle. The study objectives were to characterize equine vaginal microbiota in mares by culture-dependent and independent methods and to describe its variation in estrus and diestrus. Vaginal swabs from 8 healthy adult Arabian mares were obtained in estrus and diestrus. For culture-dependent processing, bacteria were isolated on Columbia blood agar (BA) and Man Rogosa Sharpe (MRS) agar. LAB comprised only 2% of total bacterial isolates and were not related to ovarian phases. For culture-independent processing, V3/V4 variable regions of the 16S ribosomal RNA gene were amplified and sequenced using Illumina Miseq. The diversity and composition of the vaginal microbiota did not change during the estrous cycle. Core equine vaginal microbiome consisted of Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria at the phylum level. At the genus level it was defined by Porphyromonas, Campylobacter, Arcanobacterium, Corynebacterium, Streptococcus, Fusobacterium, uncultured Kiritimatiaellae and Akkermansia. Lactobacillus comprised only 0.18% of the taxonomic composition in estrus and 0.37% in diestrus. No differences in the relative abundance of the most abundant phylum or genera were observed between estrus and diestrus samples.

Microbiota of semen from stallions in Sweden identified by MALDI-TOF

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Bacteria isolated from stallion semen vary in number and species found.

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Differences may depend on culture conditions and method of identification.

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64% bacteria in stallion semen were cultured and identified by MALDI-TOF.

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The number of bacteria varied considerably among samples, even from the same stud.

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More information is needed on their effect on sperm quality.

Stallion semen is known to contain environmental bacteria and normal commensals, and in some cases may contain opportunistic pathogens. These bacteria may negatively influence sperm quality during storage before artificial insemination. The bacteria isolated depend on the culture conditions and method of identification; therefore, the aim of this study was to identify as many of the bacteria present in stallion semen as possible by culturing aliquots of semen under a variety of conditions. Eleven semen samples were available: five extended semen samples from one stud together with a sample of the extender, and six raw semen samples from another stud. Aliquots of semen samples were cultured on different agars and under specialized conditions; individual bacterial colonies were identified using Matrix-assisted laser desorption ionization time of flight mass spectrometry. Approximately 55% of the bacteria could be identified, with 20 bacterial taxa being isolated from semen samples from the five stallions on the first stud and 11 taxa from the semen samples from six stallions on the second stud. Staphylococcus spp. were present in all samples, and Micrococcus spp. were present in all of the extended semen samples although they were also isolated from the extender. The number of bacteria in colony forming units per mL varied considerably among samples. Only one microbe known to be associated with equine infertility, Pseudomonas spp., was isolated from three samples, albeit in low numbers. In conclusion, bacterial culture followed by MALDI-TOF does not identify all bacteria present in stallion semen samples. In-depth knowledge of which microbes are likely to be present is useful in determining their effects on sperm quality and, where appropriate, developing protocols for effectively controlling microbial growth.

Impaired inflammatory state of the endometrium: a multifaceted approach to endometrial inflammation. Current insights and future directions

New insights into the complex and fine-regulated inflammatory mechanisms involved in the endometrium reveal multiple facets to the problem of endometrial inflammation. However, the entity termed chronic endometritis is to date restricted to infectious etiology and managed with antibiotics. Conversely, the concept of impaired inflammatory state of the endometrium (IISE) provides a more global approach to defective endometrial inflammation, considering both infectious and non-infectious etiology. A non-systematic review was done through a search on MEDLINE, EMBASE, Global Health, The Cochrane Library, Health Technology Assessment Database and Web of Science, research registers. Pertinent original and review articles, published in English or French until December 31, 2019, were selected. A compelling body of evidence demonstrates transient, repeated and persistent IISE to be a major factor of most problematic disorders in obstetrics/gynecology, such as endometrial polyps, unexplained infertility, miscarriage, placenta-related pathology and endometrial cancer. When scheduled accordingly, hysteroscopy can play a key role in the IISE assessment. Robust data suggests the pertinence of minimal-effective anti-inflammatory regimens for therapeutic IISE targeting. This review provides a comprehensive update on the multiple facets of inflammation in the endometrial physiology and pathology. Further research is needed to improve classification, diagnosis and treatment of IISE.

The Effects of Treatment with N-Acetyl Cysteine on Clinical Signs in Persistent Breeding-Induced Endometritis Susceptible Mares

Persistent breeding-induced endometritis (PBIE) is a major cause of infertility in mares. Endometrial inflammation that persists until embryonic descent ultimately results in early embryonic death. A poor endometrial biopsy grade (IIb or III) has been identified as a risk factor for PBIE. Intrauterine fluid accumulation (>2 cm in depth), pathologic endometrial edema, and elevated intrauterine neutrophil levels are all clinical features of PBIE. Commonly applied treatment options include uterine lavage and oxytocin therapy. N-acetyl cysteine (NAC), a mucolytic used to treat bacterial endometritis in mares, has anti-inflammatory properties and was investigated as a potential treatment for PBIE. A randomized, blinded, cross-over design clinical trial used NAC before breeding in PBIE-susceptible mares (n = 9). Intrauterine infusion of 3.3% NAC was performed 12 hours before insemination, and endometrial cytology and endometrial biopsy samples were obtained at 12 and 60 hours after insemination. Endometrial biopsies were evaluated for the degree of inflammation present. Clinical signs of endometrial edema and intrauterine fluid volumes were assessed by transrectal ultrasound at 12 and then every 24 hours after breeding. Data were analyzed using repeated measures analysis of variance and a Mann Whitney Wilcoxon Test. Treatment with NAC did not improve clinical signs in PBIE-affected mares. However, endometrial biopsies from mares treated with NAC displayed more diffuse and severe neutrophil infiltration than control cycles. Further research using a larger population of mares is required to evaluate the effects of NAC treatment on the endometrium of PBIE-susceptible mares.

Luteinizing hormone and ovarian steroids affect in vitro prostaglandin production in the equine myometrium and endometrium

Prostaglandins (PGs) play crucial roles in the regulation of the oestrus cycle and establishment of pregnancy in animals. Luteinizing hormone (LH) and ovarian steroids are involved in regulating endometrial PG production in many species. Their effects on PG production and associated pathways in the mare myometrium and endometrium are the subjects of our interest. This study aimed to evaluate the specific effects of LH and ovarian steroids on equine myometrial and endometrial tissues on (i) PGE₂ and PGF_2α secretion and (ii) transcription of genes encoding specific enzymes responsible for PG synthesis, such as prostaglandin-endoperoxide synthase (PTGS2), PGE₂ synthases (PGES), PGF_2α synthases (PGFS), and PGI₂ synthases (PGIS), using equine myometrial and endometrial explants. Equine myometrial and endometrial tissues were collected at the mid-luteal (n = 6) and follicular (n = 6) phases of the oestrus cycle and were exposed to: (1) vehicle (control), (2) arachidonic acid (AA, 50 ng/mL, positive control), (3) LH (10 ng/mL), (4) progesterone (P₄, 10^-7M) and (5) 17-β oestradiol (E₂, 10^-9M) for 24 h. After exposure, PGF_2α and PGE₂ concentrations were determined using direct enzyme immunoassays. Alterations in PG synthase mRNA expression were determined using RT-qPCR. After 24 h, LH and P₄ increased PGE₂ and PGF_2α secretion by myometrial tissues at the mid-luteal phase (P < 0.05), whereas PG secretion was augmented by LH and E₂ during the follicular phase (P < 0.01). In contrast, LH and E₂ increased PGE₂ and PGF_2α secretion by endometrial tissues during the mid-luteal phase (P < 0.05), while E₂ enhanced PGE₂ secretion during the follicular phase of the oestrus cycle (P < 0.01). These results indicate that LH and ovarian steroids modulate PG production in equine myometrial and endometrial tissues and affect PG synthase expression at the mRNA level. We conclude that the equine myometrium is an alternative source of PG production and participates in the regulation of uterus function during the oestrus cycle.

The Healthy and Diseased Equine Endometrium: A Review of Morphological Features and Molecular Analyses

Simple Summary

Diseases of the endometrium are a frequent cause of subfertility in mares and have an economic impact on the horse breeding industry. These include periglandular fibrosis of endometrial glands (endometrosis), degenerative diseases of vessels (angiosis), inflammation (endometritis), as well as altered differentiation of endometrial glands. Some mares are susceptible towards persistent endometritis. The etiology and pathogenesis of endometrosis are still unclear. This review describes morphological hallmarks and molecular features associated with endometrial health and different types of diseases. The presented literature data reveal characteristic differences in the expression of several extra- and intracellular molecules between the healthy and diseased equine endometrium. Some of these molecules can be detected directly within the tissue and thus have the potential to serve as excellent diagnostic markers for the presence of endometrial diseases. The knowledge of disease-associated changes in cellular differentiation, secretory functions, and immune mechanisms will help to decipher pathogenesis and will contribute to the development of novel treatments. In addition, the quantification of molecular alterations may contribute to a fertility prognosis for an individual mare. Reproductive health increases the well-being of mares and reduces financial loss for the horse breeding industry.

Abstract

Mares are seasonally polyestric. The breeding season in spring and summer and the winter anestrus are flanked by transitional periods. Endometrial diseases are a frequent cause of subfertility and have an economic impact on the horse breeding industry. They include different forms of endometrosis, endometritis, glandular maldifferentiation, and angiosis. Except for suppurative endometritis, these are subclinical and can only be diagnosed by the microscopic examination of an endometrial biopsy. Endometrosis is characterized by periglandular fibrosis and nonsuppurative endometritis by stromal infiltration with lymphocytes and plasma cells. The pathogenesis of endometrosis and nonsuppurative endometritis is still undetermined. Some mares are predisposed to persistent endometritis; this has likely a multifactorial etiology. Glandular differentiation has to be interpreted under consideration of the season. The presence of endometrial diseases is associated with alterations in the expression of several intra- and extracellular molecular markers. Some of them may have potential to be used as diagnostic biomarkers for equine endometrial health and disease. The aim of this review is to provide an overview on pathomorphological findings of equine endometrial diseases, to outline data on analyses of cellular and molecular mechanisms, and to discuss the impact of these data on reproduction and treatment.

Age-Dependent Effect of Foal Heat Breeding on Pregnancy and Embryo Mortality Rates in Thoroughbred Mares

The aim of the present study was to evaluate the correlation of age and heat cycle to determine reproductive efficiency in young and aged Thoroughbred mares bred on foal heat (FH) or on second heat (SH) after foaling. Embryo mortality (EmbM) was determined every time a mare was found open after a positive pregnancy diagnosis. Parturition to breeding interval, pregnancy rate (PregR) and EmbM rate were the dependent variables and the treatments were breeding on the FH or on SH. The cutoff age to obtain above-average probability for the EmbM was 10 years old. PregR in mares bred on FH was lower compared with SH (P < .01); however, it was neither affected by the age of mares (P > .05) nor by the age group of mares (P > .05). Regarding FH and SH, there was a difference in PregR in young mares (P < .01), unlike in aged mares (P > .05). EmbM rate was not different between mares bred on FH or SH (P > .05) although it was affected by age of mares (P < .01). EmbM was higher in oldest than young mares (P < .01). Aged mares bred on FH had a significantly higher EmbM rate compared with the young group also bred on FH (P < .01). In conclusion, the reproductive efficiency of Thoroughbred mares bred on FH is dependent of the age. Aged mares (≥10 years old) should be bred at their SH to reduce EmbM and improve reproductive performance.

Neutrophils, monocytes and other immune components in the equine endometrium: Friends or foes?

The innate and adaptive immune mechanisms are key components of regulation of reproductive physiological function and uterine disorders in equine uterus. The predominant immunological response in equine endometrium, characterized by an innate immune response, occurs under estrogens influence, in the follicular phase. Although, the increase in immune-related genes in equine endometrium during estrus has been suggested to play a role in uterine clearance after mating, immune cells and their product, i.e. cytokines play also mandatory role in the luteal development and maintenance, regression of equine corpus luteum, as well as in early pregnancy. Innate immune response is nonspecific and acts as the first line of defense against pathogens, foreign stimuli that include constituents of seminal fluid and local infections (endometritis). It has been recently established that a phagocytosis-independent mechanism to restrain bacteria, by means of neutrophil extracellular traps (NETs) formation, is involved in pathogenesis of in mare endometrial fibrosis (endometrosis). Moreover, persistent macrophages and mast cell activation could also have pro-fibrotic roles by secreting great amounts of pro-fibrotic factors and lead to fibrosis. This review will highlight the involvement of immune key components of the innate and adaptive immune system and their products in equine uterus and their contribution to reproductive physiological function and uterine disorders.

Preimplantation factor modulates acute inflammatory responses of equine endometrium

Persistent mating-induced endometritis (PMIE) is a significant cause of mare infertility hence its treatment would advance the management of susceptible mares. Preimplantation factor (PIF) is secreted by viable embryos, including human, mouse and cattle, and is essential for maternal immune-tolerance without immune-suppression by modulating inflammation. This preliminary study aimed to test whether PIF exerts inflammatory-modulating properties upon equine endometrium challenged with Escherichia coli-derived lipopolysaccharide (LPS) using endometrial explant culture. Follicular (n = 3), luteal (n = 4), anoestrous (n = 4) and transitional (n = 4) stage endometrial explants were established and cultured in triplicate in either serum-free medium alone (control) or medium with; 50 or 100 nmol/L synthetic PIF (sPIF); 3 μg/mL LPS; LPS and 50 or 100 nmol/L sPIF; or scrambled PIF (PIFscr; same amino acid composition arranged in a different order). Media samples were collected at 24 and 72 h, representing acute and chronic inflammatory response. Radioimmunoassay determined Prostaglandin F_2α (PGF_2α ) as an inflammatory marker. The only significant observation was the abrogation of PGF_2α response to LPS challenge by 100 nmol/L PIF for follicular stage tissue, 24 h after treatment. Further studies are therefore, warranted to realise PIF potential in managing PMIE.

Assessment of uterine luminal pH in mares and the effect of dilute vinegar lavage on uterine luminal pH and endometrial health

Uterine luminal pH has been demonstrated to be a valid indicator of uterine health in species such as cattle and sheep. However, research regarding uterine luminal pH in equines is lacking. The objectives of this study were to assess uterine luminal pH in mares during the estrous cycle, and evaluate the effect of dilute vinegar lavage on both uterine luminal pH and endometrial health. The study was conducted using a randomized block design in which eight mares (four Thoroughbred and four Standardbred) were aged matched then randomly assigned to two groups. Endometrial biopsies were taken from each mare prior to trial commencement. The treatment group (n = 4; 1 Thoroughbred, 3 Standardbreds) received a uterine lavage of one liter dilute vinegar (20 mL of vinegar in 1 L saline) every second day during each estrus period throughout the trial. Control group mares did not receive a uterine lavage. Uterine luminal pH measurements were recorded in all mares in both groups for a period of up to 10 min immediately prior to lavage (0 h), one hour and 24 h post lavage (same time points in control group mares as if they had been treated). Diestrus uterine luminal pH measurements were recorded once between days 6-10 post-ovulation. Endometrial biopsies were repeated from all mares at trial completion. Mean uterine luminal pH ranged from pH 5.3 to 7.6 and was significantly lower during diestrus compared to estrus (P < 0.001). Regression analysis indicated that this variation in pH was best explained by estrous cycle day, with uterine luminal pH increasing by a mean of 0.03 units each day (P < 0.001) from 6 to 10 days post-ovulation through to ovulation. Uterine lavage with dilute vinegar did not significantly affect uterine luminal pH (P > 0.05). A scoring system to quantify the abundance of cell types in the endometrial biopsies showed that mares in the treatment group had a significant decrease in polymorphonuclear cell abundance between pre- and post-trial biopsies (P = 0.03). Mares in the treatment group also had a significant decrease in lymphocyte, plasma cell and eosinophil cell abundance (P = 0.05). Although dilute vinegar lavage was not associated with a significant change in uterine luminal pH, it was associated with a significant improvement in endometrial biopsy scores. Because the control group did not receive a uterine lavage, further research is required to determine if this significant improvement results from the addition of dilute vinegar, or the uterine lavage itself.

The Fate of Autologous Endometrial Mesenchymal Stromal Cells After Application in the Healthy Equine Uterus

Because of their distinct differentiation, immunomodulatory, and migratory capacities, endometrial mesenchymal stromal cells (MSCs) may provide an optimum source of therapeutic cells not only in relation to the uterus but also for regeneration of other tissues. This study reports the fate of endometrial MSCs following intrauterine application in mares. Stromal cell fractions were isolated from endometrial biopsies taken from seven reproductively healthy mares, expanded, and fluorescence labeled in culture. Phosphate-buffered saline (PBS) or MSCs (15 × 10⁶) were autologously infused into each uterine horn during early diestrus and subsequently tracked by fluorescence microscopy and flow cytometry of endometrial biopsies and blood samples taken periodically after infusion. The inflammatory response to cell infusion was monitored in endometrial cytology samples. MSCs were detected in endometrial sections at 6, 12, and 24 h, but not later (7 or 14 days), after cell infusion. Cells were in all cases located in the uterine lumen, never within the endometrial tissue. No fluorescence signal was detected in blood samples at any time point after infusion. Cytology analyses showed an increase in % of polymorphonuclear neutrophils between 1 and 3 h after uterine infusion with either MSCs or PBS and a further increase by 6 h only in mares infused with PBS. In summary, endometrial MSCs were detected in the uterine lumen for up to 24 h after infusion, but did not migrate into the healthy endometrium. Moreover, MSCs effectively attenuated the inflammatory response to uterine infusion. We conclude that endometrial MSCs obtained from routine uterine biopsies could provide a safe and effective cell source for treatment of inflammatory conditions of the uterus and potentially other tissues.

Influences of intrauterine semen administration on regulatory T lymphocytes in the oestrous mare (Equus caballus)

In the mare, early pregnancy loss is common, but involvement of the maternal immune system in the pathogenesis of this condition has not been investigated in detail so far. In the present study, we assessed effects of exposure of the endometrium to semen or seminal plasma in oestrous mares on the response of regulatory T lymphocytes (Tregs) in the peripheral circulation as well as in the endometrium. Raw semen, seminal plasma or PBS (control) were introduced into the uterus of oestrous mares (n = 12). Blood was collected immediately before insemination or PBS infusion (time 0), and 12, 24 and 48 h thereafter. Endometrial biopsies were collected at 24 h. In peripheral blood, Treg (CD4⁺Foxp3⁺) cells were determined by flow cytometry. In endometrial biopsies, Tregs were assessed as cells staining positive for Foxp3 by immunohistochemistry. The percentage of Tregs in blood decreased (p < 0.05) at 12 h after exposure to seminal plasma, tended to decrease in response to raw semen (p = 0.095) but not to PBS. Leukocyte and PMN counts were not affected. In the endometrium, numbers of Foxp3 positive cells at 24 h after insemination or PBS infusion were not changed by treatment. Results of the present study provide only little evidence that maternal tolerance of pregnancy in the horse is modulated already by exposure of the oestrous endometrium to seminal plasma at mating.

Review: The epic journey of sperm through the female reproductive tract

Millions or billions of sperm are deposited by artificial insemination or natural mating into the cow reproductive tract but only a few arrive at the site of fertilization and only one fertilizes an oocyte. The remarkable journey that successful sperm take to reach an oocyte is long and tortuous, and includes movement through viscous fluid, avoiding dead ends and hostile immune cells. The privileged collection of sperm that complete this journey must pass selection steps in the vagina, cervix, uterus, utero-tubal junction and oviduct. In many locations in the female reproductive tract, sperm interact with the epithelium and the luminal fluid, which can affect sperm motility and function. Sperm must also be tolerated by the immune system of the female for an adequate time to allow fertilization to occur. This review emphasizes literature about cattle but also includes work in other species that emphasizes critical broad concepts. Although all parts of the female reproductive tract are reviewed, particular attention is given to the sperm destination, the oviduct.