Effect of immunomodulatory therapy on the endometrial inflammatory response to induced infectious endometritis in susceptible mares

Use of equine embryo -derived mesenchymal stromal cells and their extracellular vesicles as a treatment for persistent breeding-induced endometritis in susceptible mares

Persistent breeding induced endometritis (PBIE) is a significant cause of infertility in mares. The development of a safe, universal, readily available therapeutic to manage PBIE and facilitate an optimal uterine environment for embryo development may improve pregnancy rates in susceptible mares. Mesenchymal stromal cells (MSCs) are being used increasingly as a therapeutic mediator for inflammatory conditions such as endometritis, and early gestational tissue provides a unique source of multipotent stem cells for creating MSCs. Extracellular vesicles (EVs) are mediators of cell communication produced by many different cell types. This study utilized embryo-derived mesenchymal stromal cells (EDMSCs) and their EVs as a potential therapeutic modality for PBIE in two groups: a) PBIE-susceptible mares challenged with pooled dead sperm (n=5); and b) client-owned mares diagnosed as susceptible to PBIE (n=37 mares and 40 estrous cycles). Mares pre-treated with intrauterine EDMSCs or their EVs resulted in a significant reduction in the accumulation of intrauterine fluid post-breeding. Nine of 19 (47 %) mares treated with EDMSCs prior to natural breeding and 13 of 20 (65 %) mares treated with EDMSC derived EVs were pregnant after the first cycle and 12 of 18 (67 %) mares treated with EDMSCs, and 15 of 19 (79 %) mares treated with EVs conceived by the end of the breeding season. These preliminary clinical studies are the first reports of the use of EDMSCs or their EVs as a potential intrauterine therapy for the management of PBIE susceptible mares.

The efficacy of intravenous application of the Mycobacterium Cell Wall Fraction (AMPLIMUNE) in the treatment of subclinical mastitis caused by S. Aureus

The aim of the study was to investigate the effect of the immunostimulant Mycobacterium Cell Wall Fraction (MCWF) on the treatment of S. aureus SCM by intravenous application. The study included 45 HF dairy cows in 2nd and 3rd month after parturition divided into three groups (n = 15 per group): the MC + group - cows with S. aureus SCM treated with MCWF; the MC- group - cows with S. aureus SCM, with no treatment; and the C group - the control group of healthy cow with no treatment. Samples were collected 0th (I sample), 7th (II), and 14th day (III) from the day of SCM diagnosis and on day 21st (IV). A greater influx of leukocytes was confirmed into milk after 7 days after MCWF treatment in MC + group, which was followed by increase of WBC and LYM in blood. These results support the hypothesis of effective action of MCWF, and in quarters with lower-grade infection, bacteriological cure was achieved. The MC- group had a statistically higher concentration of TBARS and CAT activity in milk, while MC + group had lower blood serum LDH activity, which indicates a positive effect of the MCWF application and a lower exposure of the tissue to lipide peroxidation and inflammation caused by S. aureus. The application of MCWF would give new possibilities in the prevention and therapy of mammary gland diseases without fear of the presence of residues and the emergence of bacterial resistance. In future studies, the effects of local and systemic application of MCWF in the treatment of S. aureus SCM should be compared.

Platelet-Rich Plasma Proteome of Mares Susceptible to Persistent-Breeding-Induced Endometritis Differs from Resistant Mares

Persistent-breeding-induced endometritis (PBIE) is the leading cause of subfertility and poor reproductive efficiency in mares. Platelet-rich plasma (PRP) treatment has been shown to mitigate PBIE, reduce uterine infections, and improve fertility in mares. However, the proteome of PRP in mares, particularly those susceptible to PBIE, remains unknown. This study aimed to fill this knowledge gap by comparing the most abundant proteins present in PRP prepared from mares with histories of being susceptible or resistant to PBIE. The study involved twelve light-breed mares: seven susceptible and five resistant to PBIE. A complete blood count and physical examination were performed on each mare before blood drawing to ensure good health. The PRP was prepared following collection in a blood transfusion bag and double centrifugation. Platelet counts in the PRP were compared across the groups. The PRP was cryopreserved in liquid nitrogen until proteomics could be completed. Physical parameters and complete blood cell counts were within normal ranges. The platelet counts for resistant (561 ± 152 × 103) and susceptible mares (768 ± 395 × 103) differed (p < 0.05). One hundred and five proteins were detected in all mares, and four proteins were more abundant in resistant mares (p < 0.05). The proteins were apolipoprotein C-II, serpin family G member 1, protection of telomeres protein 1, and non-specific serine/threonine protein kinase. All these proteins are linked to the immune response. These results suggest that PRP prepared from mares resistant to PBIE may be more beneficial in mitigating PBIE in mares, offering a promising avenue for improving equine reproductive health. However, this remains to be determined with in vivo studies.

Using mycobacterium cell wall fraction to decrease equine chorionic gonadotropin after abortion

BACKGROUND

Equine embryonic loss following the development of endometrial cups delays return to cyclicity due to the production of equine chorionic gonadotropin (eCG). Natural degradation of endometrial cups coincides with an influx of immune cells at 100-120 days of gestation, but therapeutic stimulation of reduced eCG production has been relatively unsuccessful. Recently, we observed an increase in pro-inflammatory cytokine production following the use of the immunostimulant mycobacterium cell wall fraction (MCWF).

OBJECTIVES

To evaluate the efficacy of hysteroscopic-guided injection of MCWF on the accelerated decline of eCG secretion.

STUDY DESIGN

In vivo experiment.

METHODS

Mares were pharmacologically aborted at 40-45 days of gestation, and then divided into groups: MCWF-treated (6 mg MCWF suspended in 20 mL LRS; n = 10) and Control (20 mL LRS; n = 6). Five days after abortion, hysteroscopic-guided injection of endometrial cups was performed, with 1 mL of volume placed into each visible endometrial cup. This was repeated 7 days later. Trans-rectal ultrasonography was performed to monitor ovarian activity, and serum was obtained to assess eCG and cytokine concentrations.

RESULTS

Concentrations of eCG decreased in the MCWF-treated group (p < 0.01) with a significant suppression noted as early as 14 days after onset of treatment and remained suppressed for the duration of the study. This coincided with an increase in peripheral IFN-γ (p < 0.01) and IL-1β (p < 0.01) concentrations. Eight out of ten MCWF-treated mares (80%) developed pre-ovulatory follicles, in comparison to 2/6 controls (33%). A pre-ovulatory follicle was noted 23 ± 4 days after onset of treatment.

MAIN LIMITATIONS

No pregnancy data was obtained following treatment.

CONCLUSIONS

This is the first report of a treatment for the accelerated reduction of eCG following abortion. Stimulation of this process allowed mares to develop a pre-ovulatory follicle within a month of MCWF treatment onset, granting repeat attempts at breeding within the confines of a single breeding season.

Assessment of Connective Tissue in the Equine Uterus and Cervix: Review of Clinical Impact and Staining Options

Uterine diseases stand as the primary cause of infertility in mares; however, the diagnostic process often relies on obtaining endometrial biopsies and their hematoxylin-eosin staining. This review seeks to present the variability of uterine changes and their impact on fertility and underscore the utility of special stains, such as Masson trichrome, picrosirius red, elastica van Gieson, or periodic acid-Schiff, in enhancing diagnostic breadth. Connective tissue evaluation in the cervix is discussed, as it is subjected to cyclic changes and the impact on overall fertility. Vascular changes, particularly prevalent in multiparous mares, play a crucial role in adapting to physiological and pathological alterations, affecting early gestation and impeding placental development. Given that uterine vascular pathologies often involve fibrotic changes, connective tissue stains emerge as a valuable tool in this context. Moreover, equine endometriosis, predominantly associated with endometrial fibrosis, further highlights the relevance of special stains, suggesting their underutilization in the diagnostic process. Recognizing the subjective nature of diagnosing uterine pathologies and the need for additional diagnostic tools, we advocate for using dedicated stains in the histopathological evaluation of uterine samples. In conclusion, we encourage scientists and diagnosticians to embrace additional tools that enhance pathology visualization, enabling more reliable diagnoses concerning expected fertility.

Clinical and subclinical endometritis in dromedary camels: An overview of definition and clinical presentation, etiopathogenesis, diagnostic biomarkers, and treatment protocols

The current review collected and analyzed research on clinical endometritis (CE) and subclinical endometritis (SCE) in dromedary camels in terms of definition and clinical presentation, etiopathogenesis, diagnostic biomarkers, and treatment protocols. CE is characterized by uterine inflammation with abnormal vaginal discharges, while SCE comprises uterine inflammation with no clinical signs and is described as the infiltration of polymorphnuclear cells into the endometrium. CE is the prevalent clinical finding of barren female dromedaries (18-60 %). SCE has been detected in 9.9 % of infertile female dromedaries. CE and SCE are observed mainly in repeat breeding females. Unhygienic reproductive management, unsanitary dealings during parturition, and postpartum problems are major risk factors. Environmental stress, immunodeficiency, mucus abrasion, or the presence of other opportunistic microbes are predisposing factors. Trueperella pyogenes, Escherichia coli, Pseudomonas aeruginosa, Streptococcus spp., and Staphylococcus spp. are the major uterine isolates obtained from females with CE, while Bacillus spp., Staphylococcus spp., and Candida albicans are the most frequent isolates of SCE. CE and SCE reveal biomarker changes that could aid in the diagnosis of this common reproductive disorder. Only a few treatment protocols for CE and SCE have been tried and proven to work in camel practice. However, there is room for the new, challenging treatment programs proposed in this review. This review also provides a compilation that may be of use to future research and to those working in the field of camel reproduction.

Genotypic and Phenotypic Characterization of Escherichia coli Isolates Recovered from the Uterus of Mares with Fertility Problems

Escherichia coli is the bacterial pathogen most frequently associated with mare infertility. Here, we characterized 24 E. coli strains isolated from mares which presented signs of endometritis and infertility from a genotypic and phenotypic point of view. The majority of the isolates belonged to phylogenetic group B1 (9/24, 37.5%). Regarding antibiotic resistance profiles, 10 out of 24 (41.7%) were multidrug-resistant (MDR). Moreover, 17 out of 24 (70.8%) were strong or moderate biofilm producers, and of these eight were MDR strains. Interestingly, 21 out of 24 (87.5%) E. coli strains were phenotypically resistant to ampicillin and 10 of them were also resistant to amoxicillin with clavulanic acid. Regarding the presence of selected virulence factors, 50% of the examined strains carried at least three of them, with fimH detected in all strains, and followed by kpsMTII (11/24, 45.9%). No strain was able to invade HeLa cell monolayers. No relevant differences for all the investigated characteristics were shown by strains that grew directly on plates versus strains requiring the broth-enrichment step before growing on solid media. In conclusion, this work provides new insight into E. coli strains associated with mares' infertility. These results broaden the knowledge of E. coli and, consequently, add useful information to improve prevention strategies and therapeutic treatments contributing to a significant increase in the pregnancy rate in mares.

Citral protects against LPS-induced endometritis by inhibiting ferroptosis through activating Nrf2 signaling pathway

INTRODUCTION

Endometritis is the inflammatory condition of the uterus. Citral, a component of lemongrass oil, is known to exhibit anti-inflammatory activity.

AIM

The effects of citral on LPS-induced endometritis were tested and the mechanisms were investigated.

METHODS

LPS-induced endometritis mice model was established and the effects of citral were detected using this model. Inflammatory cytokines were tested by ELISA. Ferroptosis was assessed by detecting GSH, ATP, MDA, and Fe²⁺ levels. Signaling pathway was tested by western blot analysis.

RESULTS

Citral prevented LPS-induced endometritis through attenuating uterine pathological changes and inflammatory cytokine release. Meanwhile, citral prevents LPS-induced ferroptosis through attenuating MDA and Fe²⁺ levels, as well as increasing ATP and GSH levels. Furthermore, citral up-regulated Nrf2 and HO-1 expression and attenuated NF-κB activation. In addition, in Nrf2 knockdown mice, the inhibitory roles of citral on ferroptosis and endometritis were largely reversed.

CONCLUSION

Taken together, citral inhibited LPS-induced endometritis through preventing ferroptosis, which were regulated by Nrf2 signaling pathway.

Clinical Aspects of Bacterial Distribution and Antibiotic Resistance in the Reproductive System of Equids

Antibiotic administration is a standard therapeutic practice for the treatment of reproductive disorders of equids. This might lead to undesirable microbial imbalance and could favour the acquisition of antibiotic resistance. Therefore, it is imperative for clinicians to understand patterns of antibiotic resistance when considering and developing treatment regimes. Continued engagement of clinicians with novel alternative approaches to treat reproductive infections would be essential in order to address this rising threat within the One Health perspective. The objectives of the present review were to present the bacterial infections in the reproductive system of equids (horses, donkeys), to upraise the literature related to the issue of antibiotic resistance of bacteria causing these infections and to discuss the topic from a clinical perspective. Initially, the review summarised the various infections of the reproductive system of equids (genital system of females, genital system of males, mammary glands) and the causal bacteria, providing relevant information about horses and donkeys. Subsequently, the clinical therapeutics of these infections were presented, taking into account the significance of antibiotic resistance of bacteria as a limiting factor in treating the infections. Finally, approaches to circumvent antibiotic resistance in clinical settings were summarized. It was concluded that awareness regarding antibiotic resistance in equine reproductive medicine would increase, as we would recognise the multifaceted problem of resistance. Actions and initiatives within the One Health approach, minimizing the potential dissemination of resistant strains to humans and to the environment, with specific applications in medicine of equids should be appropriately instituted internationally.

Evolution of the Concepts of Endometrosis, Post Breeding Endometritis, and Susceptibility of Mares

In this paper, the evolution of our understanding about post breeding endometritis (PBE), the susceptibility of mares, and events leading to endometrosis are reviewed. When sperm arrive in the uterus, pro-inflammatory cytokines and chemokines are released. They attract neutrophils and induce modulatory cytokines which control inflammation. In susceptible mares, this physiological defense can be prolonged since the pattern of cytokine release differs from that of resistant mares being delayed and weaker for anti-inflammatory cytokines. Delayed uterine clearance due to conformational defects, deficient myometrial contractions, and failure of the cervix to relax is detected by intrauterine fluid accumulation and is an important reason for susceptibility to endometritis. Multiparous aged mares are more likely to be susceptible. Untreated prolonged PBE can lead to bacterial or fungal endometritis called persistent or chronic endometritis. Exuberant or prolonged neutrophilia and cytokine release can have deleterious and permanent effects in inducing endometrosis. Interactions of neutrophils, cytokines, and prostaglandins in the formation of collagen and extracellular matrix in the pathogenesis of fibrosis are discussed. Endometritis and endometrosis are interconnected, influencing each other. It is suggested that they represent epigenetic changes induced by age and hostile uterine environment.

Effect of peripartal administration of mycobacterium cell wall fraction on health and fertility of Holstein cows under organic-certified management

The main objective of this study was to evaluate the effect of peripartal administration of a commercially available nonspecific immune stimulant (mycobacterium cell wall fraction; MCWF [Amplimune, NovaVive Inc., Napanee, ON, Canada]) on the incidence of disease during early lactation and subsequent fertility of dairy cows. A second objective was to characterize the dynamics of circulating white blood cells (WBC) and metabolic markers following treatment administration. Cows in an United States Department of Agriculture (USDA) organic-certified dairy herd were blocked by parity and, based on sequential calving dates, randomly assigned to receive two injections (5 mL s.c.) of either a placebo (saline solution) as a control (CON; n = 71) or MCWF (n = 65) at enrollment (7 d before expected calving) and within 24 h after calving. Blood samples were collected from a subsample of the study population (MCWF = 16; CON = 18) for WBC count at enrollment, at day 2 post enrollment, and at days 1, 3, 7, and 14 after calving. Serum fatty acids, beta-hydroxybutyrate, and Ca concentrations were determined at days 1 and 7 postpartum (MCWF = 21; CON = 21). Main outcome variables included incidence risk of peripartal and early lactation health disorders and pregnancy at first artificial insemination (AI), at 100, and at 150 days in milk (DIM). In addition, the average daily milk yield up to 90 DIM and death and live culling before 305 DIM were compared. Treatment effects were assessed using multivariable logistic regression, time-to-event analyses, and repeated measures analysis of variance (ANOVA). A treatment effect on the incidence risk of some of the health disorders in the study was established. Incidence risk of metritis and clinical mastitis <28 DIM was smaller in MCWF than in CON cows (36.9% vs. 50.7% and 6.3% vs. 19.7%, respectively). On the contrary, the incidence risk of respiratory disease <28 DIM was smaller in CON (0%) than in MCWF (7.7%). Reproductive performance of multiparous cows was affected by MCWF administration: pregnancy at first AI and pregnancy at 100 and 150 DIM were greater in MCWF than in CON (35.6% vs. 19.2%; 51.1% vs. 25.0%; and 64.4% vs. 40.4%, respectively). Overall, median intervals from calving to pregnancy were 90 vs. 121 d in MCWF and CON cows, respectively. No treatment effects on the dynamics of circulating WBC or in postpartum metabolic status were established. No differences for milk yield or for the proportion of cows that survived up to 305 DIM were determined, although cows in MCWF left the herd earlier than cows in CON. In conclusion, incidence risks of metritis and mastitis in early lactation were smaller in cows receiving MCWF, whereas the incidence risk of respiratory disease was smaller in CON. Fertility significantly improved in MCWF compared with CON cows. As this study was performed in an organic-certified dairy, specific health and reproductive management practices may affect the external validity of the current findings.

Intrauterine Blood Plasma Platelet-Therapy Mitigates Persistent Breeding-Induced Endometritis, Reduces Uterine Infections, and Improves Embryo Recovery in Mares

Microorganisms, including pathogenic or opportunistic bacteria and fungi, may gain access to the uterus during breeding, and infectious endometritis plays a major role in equine subfertility. This study aimed to assess the post-breeding inflammatory response, endometrial culture, and embryo recovery of mares susceptible to persistent breeding-induced endometritis (PBIE) treated with plasma-rich (PRP) or -poor (PPP) plasma. Mares (n = 12) susceptible to PBIE had three cycles randomly assigned to receive intrauterine infusions of lactate ringer solution (LRS, control), or autologous PRP or PPP pre- (−48 and −24 h) and post-breeding (6 and 24 h). Mares were bred with fresh semen from one stallion. Intrauterine fluid accumulation (IUF) and endometrial neutrophils were assessed every 24 h up to 96 h post-breeding. Uterine cytokines (Ilβ, IL6, CXCL8, and IL10) were evaluated before (0 h), 6, and 24 h post-breeding, and endometrial culture three and nine days after breed. Embryo flushing was performed 8 days post-ovulation. Data were analyzed with mixed model, Tukey’s post-hoc test, and multivariate regression. PRP treatment reduced endometrial neutrophils, post-breeding IUF, and pro-inflammatory cytokines when compared to control-assigned cycles, but not significantly different than PPP. Controls had a significantly higher percentage of positive bacterial cultures (33%) in comparison to PRP-assigned cycles (0%), whereas cycles treated with PPP were not significantly different from the other groups (25%). The PRP-assigned cycles had significantly greater embryo recovery rates (83%) than the control (33%), though not significantly different than PPP (60%). Plasma infusion reduced the duration and intensity of the post-breeding inflammatory response and improved embryo recovery in mares susceptible to PBIE. Platelets incrementally downregulate PBIE and appear to have a dose-dependent antimicrobial property.

Allogenic mesenchymal stem cell-conditioned medium does not affect sperm parameters and mitigates early endometrial inflammatory responses in mares

This study aimed to evaluate the effects of mesenchymal stem cell-conditioned medium (MSC-CM) on sperm parameters, intrauterine polymorphonuclear neutrophils (PMN), intrauterine fluid accumulation (IUF), and fertility in mares. In experiment 1, two ejaculates from ten stallions were extended to 50 million sperm/mL using a milk-based extender. Thereafter, 20 mL of extended semen was added of MSC-CM as follows: 0, 5, 10, 15, and 20 mL. Sperm kinetics and plasma membrane integrity were evaluated immediately after dilution (T0) and 2 h post-incubation at 37 °C (T2). In experiment 2, mares characterized as resistant (n = 13) or susceptible (n = 7) to endometritis were inseminated with fresh semen 24 h post-induction of ovulation in two (Control and CM-1) and three (Control, CM-1, and CM-2) cycles in a crossover, as follows: control, no pharmacological interference; CM-1, supplementation of semen insemination dose at 3:4 (v:v, MSC-CM:semen); CM-2, 30 mL of MSC-CM was infused into the uterus 24 h before insemination. Endometrial cytology and uterine fluid were collected 6 and 24 h after insemination to evaluate the number of PMNs and concentrations of interleukins IL6, IL10, and TNFα. IUF was determined by ultrasonography 24 and 48 h after insemination. Pregnancy status was diagnosed 14 days after ovulation. The addition of MSC-CM to semen did not influence sperm parameters at T0 and T2 (P > 0.05) and reduced (CM-1; P < 0.05) the number of PMNs at 6 h post-insemination in resistant mares. In susceptible mares, PMNs at 6 and 24 h post-insemination, as well as IUF were reduced (P < 0.05) in both treated cycles (CM-1 and CM-2). In addition, MSC-CM downregulated IL6 and upregulated IL10 concentrations in the uterus of susceptible mares after insemination. There were no differences in fertility rates among groups both in resistant (Control, 77%, 10/13; CM-1, 62%, 8/13) and susceptible mares (Control, 42.8%, 3/7; CM-1, 57.1%, 4/7; CM-2, 85.7%. 6/7). In conclusion, MSC-CM did not affect sperm parameters when mixed with diluted semen, and reduced post-insemination inflammatory responses in mares.

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.

Effects of the Administration of a Non-specific Immune Stimulant Around Transportation on Health and Performance of Jersey and Jersey-Cross Heifer Calves During the Rearing Period: Randomized Clinical Trial

Our objective was to evaluate the effects of a non-specific immune stimulant (IS) administered around transportation on health scores (HS), average daily gain (ADG), disease treatment and mortality of Jersey and Jersey-cross calves during the rearing period. Newborn calves (4 d ± 1) were randomly allocated to receive either 1 mL of saline (CON; n = 438), 1 mL of IS before transport (BTIS; n = 431), or 1 mL of IS immediately after transport (ATIS; n = 436). Calves were health scored weekly for 3 weeks after transport. The data were analyzed using multivariable linear mixed models and multivariable logistic regression models. Kaplan-Meier survival analysis was performed for time to event analysis. Treatment, birth weight, breed, site of birth, serum total solids, dam parity, season of enrollment, and metaphylaxis were offered to models. Differences in respiratory and fecal HS, and ADG between treatment groups were not statistically significant. A total of 196 (15.0%) calves were treated at least once for any disease and 52 calves were treated multiple times. The proportion of calves treated for respiratory disease and/or diarrhea were 14.4, 14.4, and 16.2% for BTIS, ATIS and CON groups, respectively. Although the differences in the likelihood of treatment for both respiratory disease and/or diarrhea during the first 9 weeks of life was not statistically different between groups, we observed that more calves in the control group received disease treatments around 15 days of age compared with calves that received IS. The likelihood of treatment for respiratory diseases alone during the first 30 days of life was smaller in the calves that received IS before transportation when compared to the control group. Only 18 (1.4%) calves died within the study period. The calf mortality likelihood was not statistically different between study groups; however, fewer calves in the IS groups died when compared to CON. In conclusion, the use of IS around transportation did not influence weekly HS, ADG, and the number of disease treatments during the rearing period, but administering IS before transportation resulted in fewer treatments of respiratory diseases during the first 30 days post-transport and marginally lower mortality rates during the rearing period.

Acute endometritis induced by Escherichia coli in mares evaluated through color doppler ultrasonography

ABSTRACT The objectives of this study were to characterize the endometritis induced in mares using color Doppler ultrasonography and traditional exams. Experiment 1. Mares (n=20) were submitted to intrauterine inoculation with Escherichia coli. Uterine evaluation was performed at M0 and M1. Experiment 2. Animals were divided into two groups: control group (n=10), and treated group (n=10) using phytotherapeutic solution. In both groups, the uterine evaluation was performed at time T1, T2, and T3. Experiment 3: Uterine evaluation was compared after antibiotic therapy, phytotherapy, and M0. For statistical analysis, the Tukey test, t Student, and Anova test were applied. Experiment 1. The mean values of vascularization at M1 were significantly higher than those obtained at M0 (P<0.05). Bacterial growth was observed in all samples collected. Experiment 2. The mean value of vascularization at time T1 in both groups was significantly higher (P<0.05) compared to M2 and M3. Experiment 3. After antibiotic therapy, the vascularization of the body and uterine horns was not equivalent to the vascularization presented at M0. We can conclude that it was not possible to correlate results obtained by color Doppler ultrasonography with the traditional findings for the diagnosis of endometritis.

Fractionated semen collection as a tool to rescue fertility in stallions with seminal vesiculitis

Treatments for seminal vesiculitis have poor outcomes in stallions; thus, the development of alternative strategies is warranted. This study aimed to evaluate fractionated semen collection as a method to restore the fertility of stallions diagnosed with seminal vesiculitis. Eighteen ejaculates from six stallions (three ejaculates/stallion) diagnosed with seminal vesiculitis were harvested in fractions, as follows: Fraction A (FA), the first two jets; Fraction B (FB), the third and fourth jets; and Fraction C (FC), the fifth and remaining jets of the ejaculate. All fractions were subject to standard semen evaluations that were performed in addition to cytology and bacterial aerobic cultures. Fractions were extended and cooled to 5 °C. As a proof of concept, 20 mares (48 estrous cycles, ∼8 cycles/stallion) were bred with 1 billion sperm from FA (cooled at 5 °C for 24 h). In our study, FA had negative bacterial cultures, absent macroscopic or microscopic abnormalities; FB had positive bacterial cultures in two stallions and presence of polymorphonuclear neutrophils (PMNs) in all samples, but with no macroscopic abnormalities; and FC had positive bacterial cultures, purulent appearance, and the presence of degenerated PMNs, just as noted in the whole semen. Overall, post-cooling sperm motility results were superior (P < 0.05) for FA in comparison with FB and FC. First cycle pregnancy rates using FA varied from 66% to 86%. None of the non-pregnant mares developed endometritis. In conclusion, fractionated semen collection can be used to obtain semen free of contamination and to achieve satisfactory pregnancy rates from stallions with seminal vesiculitis.

Effect of Mycobacterium cell wall fraction on endometrial histomorphometry of mares resistant and susceptible to persistent breeding-induced endometritis

Mycobacterium cell wall fraction (MCWF) is a biological component made up of molecules with immunostimulant properties, which is therapeutically used to modulate persistent breeding-induced endometritis (PBIE). The aim of this study was to analyze the effect of this immunomodulator on the endometrial histological structure during the diestrus of PBIE-resistant and -susceptible mares that either received treatment with MCWF or not. The experiment was conducted with 10 resistant mares (RM) and 9 susceptible mares (SM). In the first estrous cycle of the trial, all mares were inseminated with dead semen as an inflammatory stimulus (Group A); at the next cycle, all mares were inseminated with dead semen and treated with a MCWF commercial immunomodulator (Group B). In both groups, endometrial biopsies were taken on day 7 post-ovulation (diestrus). Endometrial biopsies of untreated-RM (UTRM, n = 6), untreated-SM (UTSM, n = 7) MCWF-treated-RM (TRM, n = 6) and MCWF-treated-SM (TSM, n = 6) were evaluated. They were randomly chosen as representative mares of Group A and B, respectively. The height of lining and glandular epithelia, glandular diameter, glandular density and glandular area were evaluated. The histological structure revealed lymphocytic infiltration and dilated, tortuous glands with some glandular nests, particularly in UTSM. The histomorphometrical results showed no differences (ρ > 0.05) between the analyzed groups. This would indicate that post-service treatment with the MCWF immunomodulator does not modify the endometrial histoarchitecture but, apparently, its action would be mainly based on the stimulation of the cellular and humoral immune responses.

Endometritis Changes the Neurochemical Characteristics of the Caudal Mesenteric Ganglion Neurons Supplying the Gilt Uterus

Simple Summary

Uterine inflammation is a very frequent pathology in domestic animals leading to disturbances in reproductive processes and causing significant economic losses. The uterus possesses nerves from either the autonomic or sensory part of the peripheral nervous system. Most of the uterus-projecting neurons are localized in the caudal mesenteric ganglion. These neurons synthesize and release numerous biologically active substances in the uterus, which regulate uterine functions. The effect of inflammation on uterine innervation is poorly recognized. This study showed that Escherichia coli-induced uterine inflammation in pig led to a reduction in the total population of uterine neurons in the caudal mesenteric ganglion, and in the populations of these cells in the dorsal and central areas of this ganglion. In the caudal mesenteric ganglion of gilts after intrauterine bacterial injection, the population of uterine neurons presenting positive staining for dopamine-β-hydroxylase (an enzyme participating in noradrenaline synthesis) and negative staining for galanin, as well as the population of uterine neurons presenting negative staining for dopamine-β-hydroxylase but positive staining for neuropeptide Y, were decreased. In these gilts, there were increased numbers of uterine neurons which, besides dopamine-β-hydroxylase, also expressed neuropeptide Y, galanin and vasoactive intestinal peptide. The above changes suggest that inflammation of the gilt uterus may affect the function(s) of this organ by its action on the neurons of the caudal mesenteric ganglion.

Abstract

This study analyzed the influence of uterine inflammation on the neurochemical characteristics of the gilt caudal mesenteric ganglion (CaMG) uterus-supplying neurons. The horns of uteri were injected with retrograde tracer Fast Blue on day 17 of the first studied estrous cycle. Twenty-eight days later (the expected day 3 of the third studied estrous cycle), either saline or Escherichia coli suspension were administered into each uterine horn. Only the laparotomy was done in the control gilts. After 8 days, the CaMGs and uteri were harvested. The infected gilts presented a severe acute endometritis. In the CaMGs, the populations of uterine perikarya possessing dopamine-β-hydroxylase (DβH) and/or neuropeptide Y (NPY), somatostatin (SOM), galanin (GAL) and vasoactive intestinal polypeptide (VIP) were analyzed using the double immunofluorescence method. In the CaMG, bacterial injection decreased the total number of the perikarya (Fast Blue-positive), the small and large perikarya populations in the dorsal and central regions, and the small and large perikarya populations coded DβH+/GAL- and DβH-/NPY+. After bacterial treatment, there was an increase in the numbers of small and large perikarya coded DβH+/NPY+, small perikarya coded DβH+/GAL+ and DβH+/SOM- and large perikarya coded DβH+/VIP+. To summarize, uterine inflammation influences the neurochemical characteristics of the CaMG uterus-supplying neurons, which may be important for pathologically changed organ functions.

The Effect of Mycobacterium Cell Wall Fraction on Histologic, Immunologic, and Clinical Parameters of Postpartum Involution in the Mare

Maintaining yearly foal production is important for the economic success of the broodmare, and this requires breeding to occur as quickly postpartum as possible. The initial postpartum estrus occurs within 5-20 days postpartum, whereas the uterus is still undergoing repair from tissue alterations during pregnancy and parturition, a process known as involution. Attempts have been made to hasten this process, but with minimal success. Mycobacterium cell wall fraction (MCWF) is an immunomodulator that has been shown to reduce bacterial growth and alter aspects of the immune response to breeding, but it is unknown if MCWF hastens the process of involution. Therefore, the objectives of this study were to (1) investigate the effect of MCWF on tissue remodeling, (2) assess the effect of MCWF on the local immune system of the uterus, and (3) determine the optimal treatment interval needed for these processes to occur. We hypothesize that repeated treatments of MCWF postpartum will hasten the process of involution. To study this, 16 pregnant mares of mixed breeds were evaluated postpartum. Control mares (n = 4) received 1.5 mL lactated Ringer's solution intravenously on Day 1 (Day 0 = day of parturition) postpartum and again on Day 7, whereas treated mares either received 1.5 mL Settle intravenously on Day 1 and Day 7 (TX1; n = 6) or 1.5 mL Settle intravenously on Day 1 and then every 3 days until ovulation was detected (TX2; n = 6) and then evaluated until 15 days postpartum. Mares were assessed every 3 days for clinical, immunologic, and histologic parameters. Clinical parameters were assessed with transrectal ultrasonography and included ovarian activity, uterine fluid retention, and measurement of the uterine diameter, in addition to endometrial culture. Immunologic parameters included endometrial biopsies for quantitative polymerase chain reaction for expression of various cytokines (interleukin [IL]-1β, IL-1RN, IL-4, IL-6, IL-8, IL-10, tumor necrosis factor [TNF], interferon [IFN]-γ, and granulocyte-macrophage colony-stimulating factor) in addition to endometrial cytology. Formalin-fixed endometrial biopsies were histologically assessed for the retention of microcaruncles, dilation of endometrial glands, and inflammation of the mucosa, stratum compactum, and spongiosum. Statistics were performed using SAS 9.4, using a mixed model for repeated measures with mare and treatment as a random effect. All post-hoc analysis was done using a Tukey's honestly significant difference test. Involution was considered complete by Day 15 postpartum in all mares, and the day postpartum had a significant effect on almost all parameters investigated, indicating the immunologic process of involution. Treatment with MCWF decreased the magnitude of bacterial growth in addition to time to negative culture. In addition, MCWF increased the expression of IL-1β, IFNγ, and TNF. Although minimal treatment effect was noted histologically, a decrease in mucosal inflammation was seen in MCWF-treated mares. In conclusion, involution appears to be influenced by the immune system. In addition, MCWF appears to have a bactericidal effect on the postpartum mare, and this may be because of an increase in proinflammatory cytokines. It is unknown if this bactericidal property will improve fertility on the first estrous cycle postpartum, and future studies are needed to determine this.

Persistent Breeding-Induced Endometritis in Mares - a Multifaceted Challenge: From Clinical Aspects to Immunopathogenesis and Pathobiology

Post-breeding endometritis (i.e., inflammation/infection of the endometrium), is a physiological reaction taking place in the endometrium of mares within 48 hours post-breeding, aimed to clear seminal plasma, excess sperm, microorganisms, and debris from the uterine lumen in preparation for the arrival of an embryo. Mares are classified as susceptible or resistant to persistent breeding-induced endometritis (PBIE) based on their ability to clear this inflammation/infection by 48 hours post-breeding. Mares susceptible to PBIE, or those with difficulty clearing infection/inflammation, have a deficient immune response and compromised physical mechanisms of defense against infection. Molecular pathways of the innate immune response known to be involved in PBIE are discussed herein. The role of the adaptive uterine immune response on PBIE remains to be elucidated in horses. Advances in the pathobiology of microbes involved in PBIE are also revised here. Traditional and non-traditional therapeutic modalities for endometritis are contrasted and described in the context of clinical and molecular aspects. In recent years, the lack of efficacy of traditional therapeutic modalities, alongside the ever-increasing incidence of antibiotic-resistant microorganisms, has enforced the development of non-traditional therapies. Novel biological products capable of modulating the endometrial inflammatory response are also discussed here as part of the non-traditional therapies for endometritis.

Participation of acetylcholine and its receptors in the contractility of inflamed porcine uterus

This study analyzed the effect of inflammation on acetylcholine (ACh)-induced muscarinic receptors (MR)2 and MR3 conducted contractility of the porcine uterus. On Day 3 of the estrous cycle, either E.coli suspension (E.coli group) or saline (SAL group) was injected into uterine horns or laparotomy was performed (CON group). Eight days later, infected gilts developed severe acute endometritis. Compared to the period before ACh treatment, ACh (10^-5 M) increased the tension in myometrium (MYO) and endometrium/myometrium (ENDO/MYO) of the CON group (P < 0.01) and in ENDO/MYO of the SAL group (P < 0.01), the amplitude in strips of the CON (P < 0.05) and SAL (MYO: P < 0.05, ENDO/MYO: P < 0.001) groups and the frequency in strips of the CON (MYO: P < 0.01, ENDO/MYO: P < 0.001) and SAL (P < 0.01) groups. In the E.coli group, ACh (10^-5 M) reduced the amplitude in MYO (P < 0.05) and ENDO/MYO (P < 0.001), increased the frequency in MYO (P < 0.01) and ENDO/MYO (P < 0.001) and did not change (P > 0.05) the tension. ACh (10^-5 M) in ENDO/MYO of the E.coli group, reduced the tension compared to the CON group (P < 0.05) and the amplitude compared to other groups (P < 0.001), while increased the frequency in relation to the SAL group (P < 0.05). MR2 antagonist (AF-DX 44 116) and ACh (10^-5 M) reduced (by 16.92%, P < 0.01) the tension in MYO of the CON group and increased (P < 0.01) it in the E.coli group compared to the period before antagonist and ACh addition. In MYO of the SAL group, the tension was increased (P < 0.01) in response to MR3 antagonist (4-DAMP) and ACh (10^-7, 10^-6 M). In the E.coli group, these substances did not change (P > 0.05) the tension, but it was lower (P < 0.001) in MYO (ACh: 10^-7 M) and ENDO/MYO (ACh: 10^-5 M) than in the SAL group. MR2 or MR3 antagonists and ACh (10^-5 M) increased (P < 0.05-0.001) the amplitude in strips of the CON and SAL groups and reduced it in the E.coli group (P < 0.001) compared to the period before antagonists and ACh use. This parameter in the E.coli group was lower (P < 0.001) after using MR2 or MR3 antagonists and ACh (10^-6, 10^-5 M) than in other groups. Both antagonists and ACh (10^-5 M) reduced the frequency in the CON, SAL (P < 0.05) and E.coli (MR2 antagonist: P < 0.01, MR3 antagonist: P < 0.05) groups compared to period before antagonists and ACh addition. Data show that ACh reduces the contractility of the inflamed porcine uterus by MR2 and MR3, which suggests that pharmacological modulation of these receptors can be used to raise the contractility of an inflamed uterus.

Uterine clinical findings, fertility rate, leucocyte migration, and COX-2 protein levels in the endometrial tissue of susceptible mares treated with platelet-rich plasma before and after AI

Persistent mating-induced endometritis (PMIE) results in decreased fertility in horses, thereby causing a significant impact in the horse market. Platelet-rich plasma (PRP), a modulator of the inflammatory response, has been largely used in veterinary medicine. Here, we investigated the effects of PRP on uterine inflammation, conception rate, endometrial polymorphonuclear neutrophil (PMN) migration, and COX-2 protein levels in the endometrial tissue. Thirteen PMIE-susceptible mares were used for artificial insemination (AI). The mares were inseminated with fresh semen in three consecutive cycles in a cross-over study design. The following cycle classifications were used: control cycle, no pharmacological interference; pre-AI, 20 mL of PRP was infused 24 h before AI; and post-AI, 20 mL of PRP was infused four h after AI. Follicular dynamics were monitored daily by transrectal ultrasound. When a follicle larger than 35 mm was detected, ovulation was induced with deslorelin acetate (1 mg, im). AI was performed 24 h after ovulation induction. Intrauterine fluid (FLU) was evaluated by ultrasonography before and 24 h after AI. PMNs in uterine cytology (CYT) and biopsy (HIS) were also observed before and 24 h after AI. Pregnancy was determined within 14 days after ovulation. Number of COX-2 positive cells was evaluated by immunohistochemistry. Both PRP treatments resulted in a decrease of PMNs in the CYT after breeding when compared to controls. FLU did not differ between cycles; however, the conception rates were significantly higher in the PRP mares. Mares positive for endometritis decreased in both treatment groups, and a more intense positive COX-2 labeling was observed in the control group when compared to the two treatment groups. In conclusion, PRP beneficially reduces inflammatory response in PMIE mares independent of when treatments were administered, thus increasing chances of successful pregnancy.

Oestrous cycle-dependent equine uterine immune response to induced infectious endometritis

Infectious endometritis is a major cause of reduced pregnancy rates in horses. The objectives of this study were to establish a timeline of the innate immune response in the uterus of healthy horses and to investigate the oestrous cycle effect on this. Endometrial biopsies were collected from five horses before and at 3, 12, 24, 48 and 72 h after inoculation of Escherichia coli, once in oestrus and once in dioestrus. They were analysed by quantitative real-time PCR, microbiology and histology. Neutrophil numbers increased from very low levels in the absence of inflammation to severe neutrophilia 3 h after inoculation. The concentrations of mRNAs for Toll-like receptor (TLR)2, TLR4, NOD-like receptor NLRC5, tissue inhibitor of metallopeptidases 1 (TIMP1) and chemokines CCL2, CXCL9, CXCL10 and CXCL11 were all increased 3 h after inoculation of E. coli compared to levels detected prior to inoculation. Chemokine mRNA levels remained elevated for 48 h. Concentrations of mRNAs for the antimicrobial peptides equine β-defensin 1 (EBD1), lysozyme, secretory leukoprotease inhibitor (SLPI), lipocalin 2 (LCN2), lactoferrin and uteroferrin were increased between 3 and 12 h post inoculation. The gene for secreted phospholipase A₂ (sPLA₂) was expressed constitutively. P19 uterocalin mRNA levels were higher in dioestrus than in oestrus over the first 24 h of inflammation. Neutrophils and many innate immune genes responded rapidly to the introduction of E. coli into the uterus, while the oestrous cycle stage had only a relatively minor effect on the response to E. coli. This study has delineated a useful model of innate immunity in infectious endometritis of healthy animals.

Deep sequencing of the uterine immune response to bacteria during the equine oestrous cycle

Background

The steroid hormone environment in healthy horses seems to have a significant impact on the efficiency of their uterine immune response. The objective of this study was to characterize the changes in gene expression in the equine endometrium in response to the introduction of bacterial pathogens and the influence of steroid hormone concentrations on this expression.

Methods

Endometrial biopsies were collected from five horses before and 3 h after the inoculation of Escherichia coli once in oestrus (follicle >35 mm in diameter) and once in dioestrus (5 days after ovulation) and analysed using high-throughput RNA sequencing techniques (RNA-Seq).

Results

Comparison between time points revealed that 2422 genes were expressed at significantly higher levels and 2191 genes at significantly lower levels 3 h post inoculation in oestrus in comparison to pre-inoculation levels. In dioestrus, the expression of 1476 genes was up-regulated and 383 genes were down-regulated post inoculation. Many immune related genes were found to be up-regulated after the introduction of E. coli. These include pathogen recognition receptors, particularly toll-like receptors TLR2 and 4 and NOD-like receptor NLRC5. In addition, several interleukins including IL1B, IL6, IL8 and IL1ra were significantly up-regulated. Genes for chemokines, including CCL 2, CXCL 6, 9, 10, 11 and 16 and those for antimicrobial peptides, including secretory phospholipase sPLA₂, lipocalin 2, lysozyme and equine β-defensin 1, as well as the gene for tissue inhibitor for metalloproteinases TIMP-1 were also up-regulated post inoculation.

Conclusion

The results of this study emphasize the complexity of an effective uterine immune response during acute endometritis and the tight balance between pro- and anti-inflammatory factors required for efficient elimination of bacteria. It is one of the first high-throughput analyses of the uterine inflammatory response in any species and several new potential targets for treatment of inflammatory diseases of the equine uterus have been identified.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2139-3) contains supplementary material, which is available to authorized users.

The influence of leukotrienes C₄ and D₄ on the contractility of an inflamed porcine uterus

The effect of leukotriene (LT) C4 (LTC4) and LTD4 on the contractility of an inflamed porcine uterus was investigated. On Day 3 of the estrous cycle (Day 0 of the study), either saline or Escherichia coli suspension was injected into each uterine horn. Although acute endometritis developed in all bacteria-inoculated gilts, a severe acute endometritis was noted more often on Day 8 than on Day 16. Myometrial and endometrial/myometrial strips were incubated with LTC4 or LTD4 alone, or together with a cysteinyl-LT receptor antagonist (BAY-u9773). Leukotriene C4 increased the contraction intensity in the saline- and bacteria-treated uteri on Day 8; however, its effect was lower in the myometrium of inflamed uteri. Contraction frequency was found to decrease in the saline-treated uteri as opposed to inflamed ones, in which it was elevated. On Day 16, contraction intensity increased in response to LTC4 in the saline-treated uteri but was reduced in the inflamed organs. The value of this parameter was lower in the inflamed uteri than that in the saline-treated ones. Leukotriene D4 (Days 8 and 16) augmented contractility in the saline-treated uteri, but despite increasing its intensity in the inflamed organs, it decreased contraction frequency. Leukotriene C4 or LTD4, added to BAY-u9773-pretreated saline- and bacteria-treated uteri on both days, decreased the contraction intensity. On Day 16 after treatment with BAY-u9773 and LTC4, contraction intensity in the endometrium/myometrium of the inflamed uteri was lower than that in the saline-treated organs. Data show that both LTC4 and LTD4 affect the contractility of inflamed porcine uteri, though LTC4 exerts a weaker contractile effect.

The effect of treatment with immune modulators on endometrial cytokine expression in mares susceptible to persistent breeding-induced endometritis

REASONS FOR PERFORMING STUDY

Research has shown that 6 h after breeding is a critical time during the uterine innate immune response, and the failure to respond appropriately will result in persistent breeding-induced endometritis. This presents a potential opportunity to modulate the course of inflammation towards a timely resolution.

OBJECTIVES

To evaluate the effects of immune modulation on endometrial mRNA expression of inflammatory genes in susceptible mares 6 h after breeding. The hypothesis was that immune modulation alters endometrial cytokine expression in susceptible mares.

STUDY DESIGN

A randomised controlled study to evaluate the effects of mycobacterial cell wall extract and dexamethasone on endometrial gene expression after insemination in 6 mares susceptible to persistent breeding-induced endometritis.

METHODS

Six susceptible mares were selected based on their uterine inflammatory response to insemination. Mares were inseminated during 3 oestrous cycles with 1 × 10(9) nonviable spermatozoa and 1) no additional treatment (control), or in combination with 2) dexamethasone (50 mg i.v.) at the time of insemination, or 3) with mycobacterial cell wall extract (1.5 ml i.v.) administered 24 h prior to insemination. Mares received one treatment per cycle in randomised order, and each mare served as her own control. Endometrial biopsies were collected 6 h after breeding, and quantitative polymerase chain reaction analysis for interleukin (IL)1β, IL6, interferon γ, IL10 and IL1RA was performed. Relative quantification values reported fold changes in mRNA expression from the control. Data were analysed using an ANOVA and significance was set at P<0.05.

RESULTS

Expression of IL1β mRNA was lower after treatment with dexamethasone (P<0.001) and mycobacterial cell wall extract (P<0.05) when compared with control. No differences were detected in the mRNA expression of the other cytokines after any of the treatments.

CONCLUSIONS

Treatment with immune modulators alters endometrial mRNA expression of IL1β after insemination. A better understanding of the mechanisms of immune modulation in the equine uterus can help to improve treatments for persistent breeding-induced endometritis.

Influence of the uterine inflammatory response after insemination with frozen-thawed semen on serum concentrations of acute phase proteins in mares

The aim of this study was to investigate the clinical relevance of measuring blood concentrations of serum amyloid A (SAA), haptoglobin (Hp) and fibrinogen (Fib) in horse reproductive management, and changes in response to artificial insemination (AI) with frozen-thawed semen. Standardbred mares (n=18) with different reproductive status (eight healthy mares in first postpartum oestrus, five healthy barren mares and five mares with endometritis) were inseminated with frozen-thawed semen. Endometritis was evaluated during oestrus by bacteriological culture, cytology and presence of ultrasonically visible intrauterine fluid during oestrus. Concentrations of SAA, Hp and Fib were analysed in the blood in every 48h during oestrus and until 5, 6 or 7 days after AI. The day of sampling and number of blood samples varied between mares because of length of the oestrus and time of AI. Changes in concentrations of SAA, Hp and Fib were evaluated based on the day of sampling regard to AI and classification of the mares. There were no differences in SAA, Hp and Fib concentrations over time before or after AI or between the groups of mares. The insemination of mares with frozen-thawed semen did not increase the plasma concentrations of SAA, Hp and Fib above clinical threshold concentration and there were no differences between susceptible or healthy mares.

Endometrial inflammatory markers of the early immune response in mares susceptible or resistant to persistent breeding-induced endometritis

Transient endometritis after breeding is necessary for clearance of bacteria and spermatozoa; however, in a subpopulation of mares, the inflammation fails to resolve in a timely fashion. The objective of this study was to describe the uterine inflammatory response in mares susceptible or resistant to persistent breeding-induced endometritis (PBIE) during the first 24 h after induction of uterine inflammation.Twelve mares were classified as susceptible (nZ6) or resistant (nZ6) to PBIE. Mares were inseminated over five estrous cycles and endometrial biopsies were collected at one time point per cycle before (0) and 2, 6, 12, and 24 h after insemination. qPCR analysis for IL1B, IL6, IL8, IFNG, TNF (TNFA), IL10, and IL1RN was performed, and endometrial inflammatory cells were counted for each sample. Relative quantification values reported fold changes in mRNA expression from 0 h values. A general pattern of expression post insemination was observed in both groups of mares. Cytokine mRNA increased at 2 h, peaked between 2 and 12 h, and then decreased.Differences were detected between groups of mares 6 h after challenge; resistant mares had higher mRNA expression of IL6, IL1RN,and IL10 than susceptible mares. Susceptible mares had an increased number of polymorphonuclear neutrophils in the endometrium 2 and 12 h after breeding when compared with resistant mares. These findings describe an inherent difference in the initial immune response to insemination and may help explain the transient nature of inflammation in resistant mares, whereas susceptible mares develop a persistent inflammation.