Embryonic and early foetal losses in cattle and other ruminants

Factors influencing pregnancy loss between days 30 and 70 in a single cattle herd: A comprehensive analysis of sire, cow, and other contributing factors

This retrospective study utilized a mixed-effects logistic model analysis to investigate variables associated with the probability of pregnancy loss (PL) between days 30 and 70 in a dataset comprising 9507 pregnancies from a single cattle herd over 10 years. The model incorporated fixed-effect variables including cow breed (Holstein, Crossbred, and Brown Swiss), parity (1st, 2nd, 3rd, and 4th or more), insemination seasons, insemination number (≤3 vs >3), estrus nature (spontaneous vs synchronized), postpartum problems, sire breed (Holstein, Fleckvieh, Brown Swiss, and Montbéliarde), zygote genotypic (pure vs crossbred), days in milk (DIM) at insemination, actual 305-day milk yield, and sire conception rate. Additionally, random effects included sire (n = 129), cow (n = 3463), and production years (n = 10). The results revealed that cows inseminated with Brown Swiss sires or sires with lower initial conception rates had higher PL rates. Biparous cows, cows with lower 305-day milk yield, cows inseminated later in DIM, cows receiving the 4th or subsequent insemination, and cows inseminated during winter or autumn had lower PL rates. The estrus type and zygote genotype did not significantly impact PL. The random effects of cow, sire, and production years were estimated at 0.230, 0.054, and 0.112, respectively. In conclusion, the study findings suggested that improving management practices for high-yielding cows, cows in early lactation stages, and cows exposed to thermal stress conditions, along with utilizing Brown Swiss cows and sires with high initial conception rates per insemination, could potentially decrease overall PL rates on the farm. Nonetheless, the results did not support the use of Crossbred cows, sires from different breeds, or specific sires to mitigate PL rates on the farm.

Effects of intrauterine extracellular vesicle microRNAs on embryonic gene expression in low-fertility cows

Embryo survival and pre-implantation development depend on uterine luminal fluid, which is believed to play a role in early embryonic death and infertility in cows. Extracellular vesicles (EVs) in the uterine luminal fluid contain microRNAs (miRNAs), crucial mediators of intercellular communication. miRNAs regulate conceptus-maternal interactions and participate in embryonic development by suppressing gene expression. Therefore, we hypothesized that miRNAs in the intrauterine EVs of low-fertility cows would hinder embryonic survival and development. EVs were collected from the bovine uterine luminal fluid of both normal- and low-fertility cows 7 days post-estrus. Small RNA-sequencing analysis of miRNAs isolated from these EVs identified eight miRNAs that were highly expressed in normal-fertility cows (normal-fertility miRNAs) and eight with elevated expression in low-fertility cows (low-fertility miRNAs). These two sets of miRNAs were transfected into hatched blastocysts via lipofection. RNA-seq following lipofection with low-fertility miRNAs identified 424 differentially expressed genes (DEGs) relative to the control; in contrast, following lipofection with normal-fertility miRNAs, seven DEGs were identified. Pathway analysis of the DEGs identified following lipofection with low-fertility miRNAs revealed substantial enrichment of mitogen-activated protein kinase (MAPK) signaling. Expression of activator protein 1 (AP1) and interferon-tau (IFNT) mRNA was significantly lower in the low-fertility miRNA transfection group than in the control. IFNT is essential for maternal pregnancy recognition. Therefore, miRNAs in intrauterine EVs from low-fertility cows at 7 days post-estrus may inhibit embryo development and suppress IFNT expression by altering MAPK signaling.

Impact of fluazuron on oocyte maturation: May the antiparasitic affect bovine reproduction?

Fluazuron is a novel veterinary pour-on antitick formulation which can be applied simultaneously with bovine reproduction management strategies. Considering the economic importance of the livestock industry in many countries, it is important to know whether antiparasitics such as fluazuron may cause embryonic loss. The aim of this study was to evaluate the toxicological effect of fluazuron on bovine oocytes during in vitro maturation. The best fluazuron concentrations were determined in a preliminary experiment on Chinese hamster ovary (CHO)-K1 cells and further used to compare fluazuron toxicity in both study models. Results of the annexin V and alkaline single cell gel electrophoresis assays demonstrated that fluazuron caused cytotoxicity and genotoxicity in bovine cumulus cells at all the concentrations tested (50, 75 and 100 μg fluazuron/mL). The evaluation of cortical granules and mitochondria distribution showed that cytoplasmic maturation was not affected by fluazuron treatment. However, a decrease in metaphase II + polar body, degenerate oocytes as well as disorganized chromatin in polar body were observed at all concentrations tested. Whereas the fertilization process was not altered by 50 μg/mL fluazuron, the embryo development rate decreased significantly. No significant differences were observed in any of the oxidative stress parameters assessed. This study contributes to a better understanding of fluazuron in bovines, suggesting that the antiparasitic may affect bovine reproduction and might cause embryo loss.

Incidence and timing of pregnancy loss following timed artificial insemination or timed embryo transfer with a fresh or frozen in vitro-produced embryo

The aim of this study was to characterize the incidence and timing of pregnancy loss from service event (timed artificial insemination or timed embryo transfer) to parturition. Lactating Holstein-Friesian cows were randomly assigned to receive either artificial insemination (AI, n = 243) or embryo transfer (ET, n = 863) with a fresh or frozen in vitro-produced blastocyst derived from oocytes collected from the ovaries of elite dairy donors (n = 14 Holstein Friesian and n = 8 Jersey) and elite beef donors (n = 21 Angus) using transvaginal ovum pick-up. In addition, oocytes were collected from the ovaries of beef heifers of known pedigree following slaughter at a commercial abattoir (n = 119). Blood samples were collected on d 7 from all cows to determine progesterone concentration and from subsets of cows on d 18 (n = 524) and d 25 (n = 378) to determine mRNA abundance of interferon-stimulated gene-15 and pregnancy-specific protein B concentration, respectively, to provide an early pregnancy diagnosis. Transrectal ultrasonography was conducted to determine pregnancy status on d 32, d 62 and d 125 after synchronized ovulation. Parturition date was recorded for all cows that reached a term delivery. The predicted probability of pregnancy (%) varied at each time point (d7, 18, 25, 32, 62, 125, parturition) depending on treatment (AI: 77.0, 60.2, 52.3, 48.8, 47.0, 44.6, 44.0; fresh ET: 100.0, 69.5, 60.3, 56.1, 48.4, 46.8, 45.5; frozen ET: 100.0, 61.7, 52.2, 41.6, 32.9, 31.8, 30.2). Irrespective of treatment, the largest proportion of pregnancy loss occurred in the period from service event (AI on d 0 or ET on d 7) to d 18, with minimal loss occurring between d 62 and parturition (AI: 1.8%, fresh ET: 1.9%, frozen ET: 3.5%). Treatment differences in the predicted probability of pregnancy per service event were detected between fresh ET vs frozen ET on d 32 and both AI and fresh ET vs frozen ET on d 62, 125 and at parturition. There was greater probability of pregnancy loss between d 32 and 62 following ET (Fresh: 11.3%, Frozen: 18.0%) than AI (4.0%). The percentage of cows that calved following transfer of a fresh embryo (45.5%) was similar to AI (44.0%), but less when a frozen embryo was transferred (30.2%). In conclusion, AI and fresh ET led to a greater probability of a cow becoming pregnant and maintaining the pregnancy to term than frozen ET. Cows that were still pregnant on d 62 had a very strong likelihood of maintaining the pregnancy to full-term parturition, irrespective of treatment. Further work is required to improve the likelihood of pregnancy establishment and reduce embryonic and fetal mortality following transfer of a cryopreserved in vitro-produced embryo.

Establishment of functional trophoblast organoids from trophoblast cells of bovine placenta

The placenta is an organ that plays a vital role in successful pregnancies, and the failure of early placentation is a significant factor leading to abortion in ruminant species. However, the mechanisms involved in the development and differentiation of bovine placenta remain elusive due to the lack of suitable in vitro placental models. This study aimed to develop an effective method for generating the bovine functional trophoblast organoids by assembling bovine primary trophoblast cells (PBTCs) from the placenta or immortalized bovine placental trophoblast (BTCs) in a 3D culture system in vitro. PBTCs isolated from the 3-month-gestation placenta and BTCs rapidly proliferated and exhibited typical epithelioid morphology in the modified trophoblast organoid medium (TOM) for bovine. Furthermore, PBTCs and BTCs proliferating in the modified TOM were both CK7- and E-cadherin-positive. Both PBTCs or BTCs embedded into Matrigel droplets overlaid with modified TOM proliferated and formed trophoblast organoids after 15 days of culture. Moreover, the expression of syntrophoblast marker genes, including CD71, CD46, and chorionic somatomammotropin hormone 1 (CSH1), was detectable in both organoids derived from different types of trophoblast cells. Notably, the protein expression levels of various genes implicated in the establishment of early pregnancy in endometrial epithelium cells (EECs) was increased following coculture with bovine trophoblast organoids. Collectively, the bovine trophoblast organoids established in our study could serve as robust models for elucidating the essential physical functions of the placenta and the causes of pregnancy failures related to the placenta developmental disorders during early bovine pregnancy.

Tryptophan regulates the expression of IGFBP1 in bovine endometrial epithelial cells in vitro via the TDO2-AHR pathway

BACKGROUND

This study aimed to identify the roles of L-tryptophan (Trp) and its rate-limiting enzymes on the receptivity of bovine endometrial epithelial cells. Real-time PCR was conducted to analyze the differential expression of genes between different groups of bovine endometrial epithelial cells. Western blot was performed to detect Cyclooxygenase-2 (COX2) expression after treatment with Trp or kynurenine (the main metabolites of Trp). The kynurenine assay was used to examine if Trp or prostaglandin E2 (PGE2) can increase the production of kynurenine in the bovine endometrial epithelial cells.

RESULTS

Trp significantly stimulates insulin growth factor binding protein 1 (IGFBP1) expression, a common endometrial marker of conceptus elongation and uterus receptivity for ruminants. When bovine endometrial epithelial cells are treated with Trp, tryptophan hydroxylase-1 remains unchanged, but tryptophan 2,3-dioxygenase 2 (TDO2) is significantly increased, suggesting tryptophan is mainly metabolized through the kynurenine pathway. Kynurenine significantly stimulates IGFBP1 expression. Furthermore, Trp and kynurenine significantly increase the expression of aryl hydrocarbon receptor (AHR). CH223191, an AHR inhibitor, abrogates the induction of Trp and kynurenine on IGFBP1. PGE2 significantly induces the expression of TDO2, AHR, and IGFBP1.

CONCLUSIONS

The regulation between Trp / kynurenine and PGE2 may be crucial for the receptivity of the bovine uterus.

High and low performing sires differ in their contributions to early embryonic stress in the bovine

Context Sires differ in their ability to produce viable blastocysts, yet our understanding of the cellular mechanisms regulated by the sire during early embryo development is limited. Aims The first aim was to characterise autophagy and reactive oxygen species (ROS) in embryos produced by high and low performing sires under normal and stress culture conditions. The second aim was to evaluate DNA damage and lipid peroxidation as mechanisms that may be impacted by increased cellular stress, specifically oxidative stress. Methods Embryos were produced using four high and four low performing sires based on their ability to produce embryos. Autophagy and ROS were measured throughout development. To evaluate oxidative stress response, autophagy, and ROS were measured in 2-6 cell embryos exposed to heat stress. To understand how cellular stress impacts development, DNA damage and lipid peroxidation were assessed. Key results Under normal conditions, embryos from low performing sires had increased ROS and autophagy. Under heat stress, embryos from low performing sires had increased ROS, yet those from high performing sires had increased autophagy. There was no difference in DNA damage or lipid peroxidation. Conclusions Results suggest that embryos from low performing sires may begin development under increased cellular stress, and autophagy potentially increases to mitigate the impacts of stress. Implications There is potential for improving embryonic competence through selection of sires with lower stress-related markers.

FGF18 impairs blastocyst viability, DNA double-strand breaks and maternal recognition of pregnancy genes

Embryonic mortality in cattle is high, reaching 10-40 % in vivo and 60-70 % in vitro. Death of embryos involves reduced expression of genes related to embryonic viability, inhibition of DNA repair and increased DNA damage. In follicular granulosa cells, FGF18 from the theca layer increases apoptosis and DNA damage, so we hypothesized that FGF18 may also affect the oocyte and contribute to early embryonic death. The aims of this study were to identify the effects of FGF18 on cumulus expansion, oocyte maturation and embryo development from cleavage to blastocyst stage using a conventional bovine in vitro embryo production system using ovaries of abattoir origin. Addition of FGF18 during in-vitro maturation did not affect FSH-induced cumulus expansion or rates of nuclear maturation. When FGF18 was present in the culture system, rates of cleavage were not affected however, blastocyst and expanded blastocyst development was substantially inhibited (P < 0.05), indicating a delay of blastulation. The number of phosphorylated histone H2AFX foci per nucleus, a marker of DNA damage, was higher in cleavage-stage embryos cultured with FGF18 than in those from control group (P < 0.05). Furthermore, FGF18 decreased accumulation of PTGS2 and IFNT2 mRNA in blastocysts. In conclusion, these novel findings suggest that FGF18 plays a role in the regulation of embryonic death during the early stages of development by impairing DNA double-strand break repair and expression of genes associated with embryo viability and maternal recognition of pregnancy during the progression from oocyte to expanded blastocysts.

From the laboratory to the field: how to mitigate pregnancy losses in embryo transfer programs?

Pregnancy losses negatively affect the cattle industry, impacting economic indices and consequently the entire production chain. Early embryonic failure has been an important challenge in the embryo industry because proper identification of embryo death at the beginning of gestation is difficult. This review aimed to provide a better understanding on reproductive failure and the relationship between early embryonic loss and different reproductive biotechniques. This review also considers insights and possible strategies for reducing early embryonic loss. The strategies addressed are as follows: i) great impact of rigorous embryo evaluation on reducing embryo losses; ii) selection of recipients at the time of transfer, taking into account health and nutritional status, and classification of the corpus luteum using ultrasound, either in area or vascularization; and iii) paternal effect as one of the factors that contribute to pregnancy losses, with a focus on embryo transfer.

Molecular approaches to mammalian uterine receptivity for conceptus implantation

Mammalian reproduction is more inefficient than expected and embryo/conceptus implantation into the maternal endometrium is considered to be a rate-limiting process. Although extensive physiological and structural diversity exists among mammalian species, the basic molecular mechanisms underlying successful implantation are conserved. The extensive use of genetically engineered mouse models has provided considerable information on uterine receptivity for embryo implantation. The molecular mechanisms and cellular processes identified thus far require further validation in other mammalian species. In this review, representative ovarian steroid hormone-induced signaling pathways controlling uterine adaptation are presented based on the results of rodent studies. Selected examples of functional conservation in mammals, such as humans and cattle, are briefly described. To date, molecular therapeutic trials for fertility improvement have not been conducted. Considerable efforts are required to provide further understanding of these molecular mechanisms. Such understanding will contribute to the development of reliable clinical diagnostics and therapeutics for implantation failure, leading to reproductive success in a wide variety of mammals in the future.

Evaluation of pregnancy associated glycoproteins assays for on farm determination of pregnancy status in beef cattle

Transrectal ultrasonography is known as the gold standard for pregnancy detection, but requires costly equipment and technical skills; therefore, access to an inexpensive and more user-friendly method with similar accuracy could benefit cattle producers. Detection of pregnancy-associated glycoproteins can accurately determine pregnancy in ruminants; however, usually requires specialized equipment for the assay. Thus, the objectives of these studies were to 1) validate the IDEXX Alertys OnFarm Pregnancy Test (lateral flow) and compare the accuracy of all three commercial PAG assays to transrectal ultrasonography and 2) to determine the postpartum interval necessary for clearance of pregnancy-associated glycoproteins from the previous pregnancy to avoid false positives. In study 1, blood samples from previously identified pregnant Bos taurus females from six different herds (nulliparous n = 1,205 and multiparous n = 1,539; samples collected between d 27 to 285 of gestation over a three-year period) were utilized. In study 2, postpartum females (primiparous n = 48 and multiparous n = 66) from one herd were utilized: (n = 1,066; samples collected weekly for up to 12 weeks postpartum). In study 1, level of agreement between different methods of pregnancy detection was determined by Pearson's correlation and Kappa scores. In study 2, data were analyzed as a repeated measure using the MIXED procedure of SAS with main effects of parity, days postpartum (dpp), and parity by days postpartum, then data were analyzed further using the REG procedure of SAS. In study 1, transrectal ultrasonography and lateral flow were positively correlated (r = 0.77; P <0.01), with 92.4% agreement. In study 2, the abundance of absorbance of PAGs rapidly decreased from 0 to 50 days postpartum, then continued to gradually decrease (P <0.01; r = 0.90). Prior to 42 days postpartum, PAG concentrations were sufficiently elevated resulting in false positive readings in all assays. In conclusion, there is very good agreement between transrectal ultrasonography and PAG assays, but likelihood of false positive results are highif assays are performed fewer than 42 days postpartum.

Effects of administration of mycobacterium cell wall fraction during the periovulatory period on embryo development following superovulation in virgin dairy heifers

Proinflammatory cytokines are involved in regulating several reproductive processes that occur during the periovulatory period, including ovulation, corpus luteum formation, and preimplantation embryo development. The objective of this study was to determine whether stimulation of proinflammatory cytokines through administration of mycobacterium cell wall fraction (MCWF; Amplimune, NovaVive) could improve embryo development following superovulation in dairy heifers. A total of 34 independent embryo recovery procedures were performed using nulliparous Holstein heifers (n = 20; age 12-18 mo) as donors. For superovulation, dominant follicle removal was performed and an intravaginal progesterone device was inserted on d -6. Thirty-six hours later, on d -4, FSH (420 IU total) was administered in a decreasing dose regimen consisting of 8 injections given twice daily at 12-h intervals. Prostaglandin F2α was administered in conjunction with the fifth and sixth injections of FSH on d -2 and the intravaginal progesterone device was removed on the morning of d -1. Twenty-four hours later, on d 0, donors received their randomly assigned treatment (sterile saline or MCWF, 5 mL, i.m.) and gonadotropin-releasing hormone was administered to induce ovulation. Donors were artificially inseminated with frozen-thawed semen at 12 and 24 h after induced ovulation. Nonsurgical embryo recovery procedures were performed on d 7. Recovered structures were evaluated using a stereomicroscope to assess embryo development. There was no effect of MCWF treatment on the numbers of total structures, unfertilized oocytes, degenerate embryos, transferable embryos, or blastocysts. However, there was a trend for donors treated with MCWF to have a greater proportion of blastocysts out of total structures recovered. Overall, the efficacy of superovulation in virgin dairy heifer donors was not improved by administration of MCWF during the peri-ovulatory period, but results indicate that MCWF treatment may enhance embryo developmental kinetics.

Association between body condition profiles, milk production and reproduction performance in Holstein and Normande cows

Body-condition dynamics are known to affect the different steps of reproduction in cattle (cyclicity, estrus expression, fertilization, embryo development). This has led to a widespread idea that there is an ideal-target optimal body condition, but no clear profile has yet been identified. Here we investigated the relationships between body condition score (BCS) profiles and reproductive performance in dairy cows. Data were from Holstein or Normande herds in 6 French experimental farms. In the Holstein breed, we discriminated 4 BCS profiles based on combining BCS at calving (Low: around 2.6 points, or High: around 3.3 points) with BCS loss after calving (Moderate (M): ≤ 1.0 points, or Severe (S): > 1.0 points). The Low-M profile mostly included multiparous cows with higher milk yield and lower reproductive performance than cows in the 3 other profiles. Low-M cows that experienced abnormal ovarian activity had lower reproductive performance than their profile-mates. Moreover, 67% of Low-M cows kept the same profile at the following lactation. The High-S profile mostly included primiparous cows with lower milk yield and higher reproductive performance than cows in other profiles. In High-S cows, higher milk yields correlated to higher risk of failure to calf on first insemination. Moreover, 38% of High-S cows kept the same profile at the following lactation, and none changed to Low-M. The other 2 BCS profiles (Low-S and High-M) were intermediate in terms of milk yield and reproductive performance. In Normande, we discriminated 3 BCS profiles based on combining BCS at calving (Low: around 2.6 points, or High: around 3.5 points) with BCS loss after calving (Flat (F): flat with no loss, Moderate (M): around 0.5 points, or Severe (S): around 1.0 point). The Low-M and High-S profiles included cows with similar performance, even though High-S-profile cows showed better but not significantly different milk yield and reproduction performance. The High-F profile included cows that were more likely to experience abnormal ovarian activity and fail at first insemination than cows in other profiles. More than 50% of Normande cows with 2 successive lactations kept in the same BCS profile at the next lactation. Even though a low BCS at calving combined with severe BCS loss (more than 1 point) after calving was found to increase reproductive failure, there was no evidence of an optimal BCS profile for reproduction in dairy cows, and reproductive success or failure is multifactorial.

Factors influencing pregnancy per artificial insemination (AI) and embryonic mortality in Nelore females subjected to timed-AI in Brazil

A greater understanding of factors influencing fertility is essential to improve pregnancy rates and reduce the occurrence of embryonic mortality in beef herds. The objective of the current study was to evaluate retrospective data of pregnancy per artificial insemination (P/AI) and pregnancy loss in Nelore females subjected to timed-AI (TAI) in Brazil. Data from 40,104 TAI collected from six breeding seasons (2016-2022) were analyzed, and the effects of animal category (e.g., classification based on age and parity), farm, month of parturition, sire, sire breed (Nelore vs Angus), estrus expression at TAI, animal temperament, and body condition scores (BCS) were evaluated. P/AI and pregnancy loss were affected (P < 0.001) by animal category. There was also an effect of farm (P = 0.0013) on P/AI and pregnancy loss (P = 0.001), as P/AI ranged from 49.28% and 55.58% and pregnancy loss from 3.37% to 6.89% across the herds evaluated. Month of parturition also affected (P < 0.001) P/AI and was higher for cows that became pregnant at the beginning of the previous breeding season. Calmer animals, presenting lower velocity scores while exiting the chute following TAI, achieved higher P/AI (P < 0.001). Lower BCS at TAI was associated (P < 0.001) with increased pregnancy loss, and BCS gain following AI was associated (P < 0.001) with reduced rates of embryonic mortality. There was a major effect (P < 0.001) of sire on P/AI and pregnancy loss, as P/AI ranged from 11% to 79%, and embryonic mortality from 0% to 40% for the bulls used in the study, highlighting the importance of the sire fertility on overall pregnancy success. Results from the current study reinforce the idea that animal age and parity at the beginning of the breeding season, BCS at the onset of estrous synchronization, BCS gain following AI, estrus expression at TAI, sire, and month of parturition are important factors influencing P/AI and rates of embryonic mortality in beef herds.

Gonadotropin-Releasing Hormone (GnRH) and Its Agonists in Bovine Reproduction II: Diverse Applications during Insemination, Post-Insemination, Pregnancy, and Postpartum Periods

The administration of GnRH and its agonists benefits various aspects of bovine reproductive programs, encompassing physiological stages such as estrous synchronization, post-insemination, pregnancy, and the postpartum period. The positive impact of GnRH administration in overcoming challenges like repeat breeder cows, early embryonic loss prevention, and the management of cystic ovarian disease (COD) is thoroughly surveyed. Furthermore, this review focuses on the significance of GnRH administration during the postpartum period, its role in ovulation induction, and how it enhances the productivity of embryo transfer (ET) programs. An emerging feature of this field is introduced, focusing on nano-drug delivery systems for GnRH agonists, and the potential benefits that may arise from such advancements are highlighted. While this review offers valuable insights into various applications of GnRH in bovine reproduction, it emphasizes the crucial need for further research and development in this field to advance reproductive efficiency and health management in dairy cattle.

Emerging Contributions of Pluripotent Stem Cells to Reproductive Technologies in Veterinary Medicine

The generation of mature gametes and competent embryos in vitro from pluripotent stem cells has been successfully achieved in a few species, mainly in mice, with recent advances in humans and scarce preliminary reports in other domestic species. These biotechnologies are very attractive as they facilitate the understanding of developmental mechanisms and stages that are generally inaccessible during early embryogenesis, thus enabling advanced reproductive technologies and contributing to the generation of animals of high genetic merit in a short period. Studies on the production of in vitro embryos in pigs and cattle are currently used as study models for humans since they present more similar characteristics when compared to rodents in both the initial embryo development and adult life. This review discusses the most relevant biotechnologies used in veterinary medicine, focusing on the generation of germ-cell-like cells in vitro through the acquisition of totipotent status and the production of embryos in vitro from pluripotent stem cells, thus highlighting the main uses of pluripotent stem cells in livestock species and reproductive medicine.

Pregnancy maintenance and fetal loss assessment in Holstein cows through analyzing pregnancy-associated glycoproteins in milk

Fetal loss (FL) from the 45th day of gestation until calving can impose a significant economic burden on dairy farmers, resulting in lost profits and increased production costs. Pregnancy-associated glycoprotein (PAG) is commonly used for detecting pregnancy in cows. PAG is secreted by binucleated trophoblast cells of the placenta and regulated by more than 24 genes. The purpose of this study was to determine the PAG threshold for FL and a probability of pregnancy maintenance until calving based on milk PAG levels. Our results reveal that primiparous and multiparous cows that maintained pregnancy until the 40th week exhibited higher PAG sample-negative (SN) values in their milk in the 6th week of gestation than did those that experienced FL later in gestation. Pregnant cows with higher PAG SN values in the 6th week of gestation were more likely to maintain their pregnancies. The area under the receiver operating characteristic curve for predicting the probability of pregnancy maintenance was 0.722 for our prediction model. On the other hand, a milk PAG SN value of <0.192 indicated 95 % confidence that FL would occur between the 7th and 40th weeks of gestation. Milk PAG testing is a noninvasive sampling technique that does not induce additional stress in lactating cows. The study reveals that PAG SN values increase significantly in Holstein cows during the 6th week of gestation. The predictive model developed was effective in forecasting pregnancy outcomes up to the 40th week of gestation or calving. The model's performance is moderately good for field application and could be a useful tool for dairy producers.

Enhancement of progesterone biosynthesis via kisspeptin stimulation: Upregulation of steroidogenic transcripts and phosphorylated extracellular signal-regulated kinase (p-ERK1/2) expression in the buffalo luteal cells

The presence of Kisspeptin (Kp) and its receptors in the corpus luteum (CL) of buffalo has recently been demonstrated. In this study, we investigated the role of Kp in the modulation of progesterone (P4) synthesis in vitro. The primary culture of bubaline luteal cells (LCs) was treated with 10, 50, and 100 nM of Kp and Kp antagonist (KpA) alongside a vehicle control. The combined effect of Kp and KpA was assessed at 100 nM concentration. Intracellular response to Kp treatment in the LCs was assessed by examining transcript profiles (LHR, STAR, CYP11A1, HSD3B1, and ERK1/2) using quantitative polymerase chain reaction (qPCR). In addition, the immunolocalization of ERK1/2 and phosphorylated ERK1/2 (p-ERK1/2) in the LCs was studied using immunocytochemistry. Accumulation of P4 from the culture supernatant was determined using enzyme-linked immunosorbent assay (ELISA). The results indicated that LCs had a greater p-ERK1/2 expression in the Kp treatment groups. A significant increase in the P4 concentration was recorded at 50 nM and 100 nM Kp, while KpA did not affect the basal concentration of P4. However, the addition of KpA to the Kp-treated group at 100 nM concentration suppressed the Kp-induced P4 accumulation into a concentration similar to the control. There was significant upregulation of ERK1/2 and CYP11A1 expressions in the Kp-treated LCs at 100 nM (18.1 and 37fold, respectively, p < 0.01). However, the addition of KpA to Kp-treated LCs modulated ERK1/2, LHR, STAR, CYP11A1, and HSD3B1 at 100 nM concentration. It can be concluded that Kp at 100 nM stimulated P4 production, while the addition of KpA suppressed Kp-induced P4 production in the buffalo LCs culture. Furthermore, an increment in p-ERK1/2 expression in the LCs indicated activation of the Kp signaling pathway was associated with luteal steroidogenesis.

Impact of the Sire on Pregnancy Loss

For over a century, scientists have attempted to develop techniques to accurately predict the fertility potential of a male's semen sample. In most livestock species, the sire is responsible for multiple pregnancies per year and up to hundreds of thousands of pregnancies if used for artificial insemination. Use of subfertile or infertile sires can have devastating impacts in regard to the reproductive efficiency of a cow herd. Despite the rapid expansion of fertility studies through advancements in molecular, genomic, and computer techniques, our understanding of male fertility is still far from complete. This article will provide an overview of the impact of the sire in pregnancy loss.

Oocyte competence and gene expression in parthenogenetic produced embryos from repeat breeder and normally fertile buffaloes (Bubalus bubalis) raised in sub-humid tropical climate

The reproductive management of the buffalo species still faces several unresolved problems, which directly affect the productivity of the herd, one of them being the presence of repeat breeder females. Given this scenario, this study aimed to verify the developmental competence of oocytes obtained from repeat breeder females and submitted to parthenogenetic activation. In addition, embryo gene expression was compared to normally fertile females. Murrah buffaloes were divided into two groups: repeat breeder (RB, n = 8) and normally fertile or control (CR, n = 7). Cumulus-oocyte complexes (COCs) were aspirated by transvaginal ovum pick-up from estrus synchronized females. The COCs were submitted to IVM for 24 h, and subsequently, the oocytes were activated using ionomycin, followed by 6-DMAP. Afterwards, the presumptive parthenotes were cultured for six or seven days in a microenvironment of 5 % CO2, 5 % O2, and 90 % N2 at 38.5 °C. The expression of OCT4, GLUT1, BCL2 and TFAM genes from blastocysts was evaluated. The overall COCs recovery rate was 70.9 % (190/268). The maturation (57.8 vs 71.1), cleavage (45.2 vs 62.2) and blastocyst (30.1 vs 45.9) rates did not differ (P > 0.05) between RB and CR females, respectively. Similarly, no significant difference (P > 0.05) was observed for the expression of studied genes in both RB and CR females. In conclusion, oocytes obtained from RB were as developmentally competent as those collected from CR females, with similar energy metabolism and in vitro development capacity. Thus, the low fertility rate of repeat breeder buffaloes, when compared to normal cyclic females, must be due to subsequent events to the blastocyst stage.

Central Role for Glycolysis and Fatty Acids in LH-responsive Progesterone Synthesis

Progesterone production by the corpus luteum is fundamental for establishing and maintaining pregnancy. The pituitary gonadotropin luteinizing hormone (LH) is recognized as the primary stimulus for luteal formation and progesterone synthesis, regardless of species. Previous studies demonstrated an elevation in abundance of genes related to glucose and lipid metabolism during the follicular to luteal transition. However, the metabolic phenotype of these highly steroidogenic cells has not been studied. Herein, we determined acute metabolic changes induced by LH in primary luteal cells and defined pathways required for progesterone synthesis. Untargeted metabolomics analysis revealed that LH induces rapid changes in vital metabolic pathways, including glycolysis, tricarboxylic acid (TCA) cycle, pentose phosphate pathway, de novo lipogenesis, and hydrolysis of phospholipids. LH stimulated glucose uptake, enhanced glycolysis, and flux of [U- 13 C 6 ]-labeled glucose-derived carbons into metabolic branches associated with adenosine 5'-triphosphate (ATP) and NADH/NADPH production, synthesis of nucleotides, proteins, and lipids, glycosylation of proteins or lipids, and redox homeostasis. Selective use of small molecule inhibitors targeting the most significantly changed pathways, such as glycolysis, TCA cycle, and lipogenesis, uncovered cellular metabolic routes required for LH-stimulated steroidogenesis. Furthermore, LH via the protein kinase A (PKA) pathway triggered post- translational modification of acetyl-CoA carboxylase alpha (ACACA) and ATP citrate lyase (ACLY), enzymes involved in de novo synthesis of fatty acids. Inhibition of ACLY and fatty acid transport into mitochondria reduced LH-stimulated ATP, cAMP production, PKA activation, and progesterone synthesis. Taken together, these findings reveal novel hormone-sensitive metabolic pathways essential for maintaining LHCGR/PKA signaling and steroidogenesis in ovarian luteal cells.

Significance

The establishment and maintenance of pregnancy require a well-developed corpus luteum, an endocrine gland within the ovary that produces progesterone. Although there is increased awareness of intracellular signaling events initiating the massive production of progesterone during the reproductive cycle and pregnancy, there are critical gaps in our knowledge of the metabolic and lipidomic pathways required for initiating and maintaining luteal progesterone synthesis. Here, we describe rapid, hormonally triggered metabolic pathways, and define metabolic targets crucial for progesterone synthesis by ovarian steroidogenic cells. Understanding hormonal control of metabolic pathways may help elucidate approaches for improving ovarian function and successful reproduction or identifying metabolic targets for developing nonhormonal contraceptives.

Supplementation with long-acting injectable progesterone 3 days after TAI impaired luteal function in buffaloes

Three experiments were conducted to evaluate the effects of long-acting injectable progesterone (iP4) in buffalo cows. In Experiment 1, ovariectomized buffaloes received 300 mg (iP300) or 600 mg (iP600) of iP4, and serum P4 concentrations were evaluated. In experiment 2, three groups were compared: control or administration of 300 mg of iP4 3 (iP4-D3) or 6 days (iP4-D6) after timed artificial insemination (TAI). On day 16, reproductive tract was recovered for conceptus, endometrium, and corpus luteum (CL) analysis. In experiment 3, pregnancy per AI (P/TAI) and proportion of pregnancy losses were evaluated after administration of 300 mg of iP4 3 (iP4-D3) or 6 days (iP4-D6) after TAI in lactating buffaloes. In experiment 1, serum P4 concentrations remained over 1 ng/mL for ~ 3 days in both groups. The 300 mg dose was used in subsequent experiments. In experiment 2, CL weight and endometrial glands density were decreased, and conceptus length was increased in iP4-D3 compared to control and to iP4-D6 (P < 0.05). Transcript abundance of Prostaglandin F Receptor (FP) and ISG15 in CL and of ISG15 and MX1 in endometrium was greater in iP4-D3 when compared to control and to iP4-D6 (P < 0.05). In experiment 3, there was no difference among experimental groups for P/TAI at D30 and pregnancy losses (P > 0.1); however, iP4-D3 presented a lower P/TAI at day 60 (41.7%) when compared to control (56.8%) and iP4-D6 (57.7%; P = 0.07). In conclusion, administration iP4 at 3 days after TAI affects CL development and consequently decreases final pregnancy outcome in buffaloes.

Cathepsin L regulates oocyte meiosis and preimplantation embryo development

Early embryonic loss, caused by reduced embryo developmental competence, is the major cause of subfertility in humans and animals. This embryo developmental competence is determined during oocyte maturation and the first embryo divisions. Therefore, it is essential to identify the underlying molecules regulating these critical developmental stages. Cathepsin L (CTSL), a lysosomal cysteine protease, is involved in regulating cell cycle progression, proliferation and invasion of different cell types. However, CTSL role in mammalian embryo development is unknown. Using bovine in vitro maturation and culture systems, we show that CTSL is a key regulator for embryo developmental competence. We employed a specific CTSL detection assay in live cells to show that CTSL activity correlates with meiotic progression and early embryo development. Inhibiting CTSL activity during oocyte maturation or early embryo development significantly impaired oocyte and embryo developmental competence as evidenced by lower cleavage, blastocyst and hatched blastocyst rates. Moreover, enhancing CTSL activity, using recombinant CTSL (rCTSL), during oocyte maturation or early embryo development significantly improved oocyte and embryo developmental competence. Importantly, rCTSL supplementation during oocyte maturation and early embryo development significantly improved the developmental competence of heat-shocked oocytes/embryos which are notoriously known for reduced quality. Altogether, these results provide novel evidence that CTSL plays a pivotal role in regulating oocyte meiosis and early embryonic development.

Proteomic Approaches to Unravel the Molecular Dynamics of Early Pregnancy in Farm Animals: An In-Depth Review

Infertility is a major problem in farm animals, which has a negative economic effect on farm industries. Infertility can be defined as the inability of animals to achieve a successful pregnancy. Early pregnancy is crucial to establish a successful pregnancy, and it is reported that 70-80% and 20-30% of total embryonic loss occur in cattle and pigs, respectively, during the first month of pregnancy. The advanced high-throughput proteomics techniques provide valuable tools for in-depth understanding of the implantation process in farm animals. In the present review, our goal was to compile, assess, and integrate the latest proteomic research on farm animals, specifically focused on female reproduction, which involves endometrial tissues, uterine fluids, oviductal fluids, and microRNAs. The series of studies has provided in-depth insights into the events of the implantation process by unfolding the molecular landscape of the uterine tract. The discussed data are related to pregnant vs. non-pregnant animals, pregnancy vs. oestrous cycle, different days of the early pregnancy phase, and animals with uterine infections affecting reproduction health. Some of the studies have utilized non-invasive methods and in vitro models to decipher the molecular events of embryo-maternal interaction. The proteomics data are valuable sources for discovering biomarkers for infertility in ruminants and new regulatory pathways governing embryo-uterine interaction, endometrium receptivity, and embryonic development. Here, we envisage that the identified protein signatures can serve as potential therapeutic targets and biomarkers to develop new therapeutics against pregnancy diseases.

Laterality in roe deer embryos implantation

Female reproductive success is one of the most important life-history traits to be monitored when determining population dynamics in free-ranging ungulates. Several studies have described how phenotypic characteristics of the mother, climatic conditions, population status, and habitat can impact on potential reproductive output in wild ungulates. However, little is known regarding the internal, physiological factors, that may account for differences in implantation rates. The present study investigated the differences in implantation rates and site on the basis of site and number of ovulations through the examination of about 3000 intact uteri collected from pregnant roe deer does (Capreolus capreolus). Although ovulation occurs with the same frequency in the left and right ovary, we revealed a higher frequency of embryos implantation in the left uterine horn in odd litter size, demonstrating that embryos can migrate between the uterine horns. In our study, a greater proportion of reproductive wastage was associated to females with three and four corpora lutea and interestingly, in relation to the site of ovulation, the percentage of corpora lutea that did not correspond to a fetus was higher in the right ovary than in the left one (73.2% vs. 26.8%). Our research described for the first time the absence of laterality in ovulation and the presence of laterality in implantation in roe deer, thus laying the foundations for in-depth studies about the functionality of this uterine side and for comparisons with populations located in other geographical areas to understand whether it is a widespread phenomenon or a local adaptation.

Metabolomic evolution of the postpartum dairy cow uterus

High rates of early pregnancy loss are a critical issue in dairy herds, particularly in seasonal, grazing systems. Components of the uterine luminal fluid (ULF), on which the early embryo depends for sustenance and growth, partly determine early pregnancy losses. Here, changes in ULF from early to mid-postpartum in crossbred dairy cows were explored, linking them with divergent embryo development. For this, the uteri of 87 cows at Day 7 of pregnancy at first and third estrus postpartum were flushed to collect ULF. Eighteen metabolites (chiefly organic acids and sugars) significantly varied in abundance across postpartum, indicating a molecular signature of physiological recovery consistent of the upregulation of pyrimidine metabolism and glycerophospholipid metabolism, and downregulation of pentose phosphate and taurine metabolism pathways. Joint pathway analysis of metabolomics data and a previously generated proteomics data set on the same ULF samples suggests key links between postpartum recovery and subsequent successful embryo development. These include upregulation of VEGFA and downregulation of metabolism, NRF2, T-cell receptor, which appear to improve the ULF's capacity of sustaining normal embryo development, and a putative osmo-protectant role of beta-alanine. These relationships should be further investigated to develop tools to detect and reduce early pregnancy loss in dairy cows.

5d CIDR-Heatsynch improves the circulatory estradiol levels, estrus expression and conception rate in anestrus buffalo (Bubalus bubalis)

The present study aimed to investigate whether increasing estradiol (E2) during preovulatory period would increase estrous expression, luteal profiles and conception rate in 5d CIDR based timed AI protocol. A total 156 anestrus buffalo allocated (78 per group) to either 5d CIDR-Cosynch (d-5: CIDR + GnRH; d0: PGF2α+CIDR removal; 72 h post-CIDR removal: GnRH) or 5d CIDR-Heatsynch (d-5: CIDR + GnRH; d0: PGF2α+CIDR removal; 24 h post-CIDR removal: estradiol benzoate) group. All the buffaloes inseminated at 72 and 84 h post-CIDR removal. A subset of buffalo (n = 58) were subjected to examination of the follicle diameter and luteal profile during protocol, post-AI on days 5 and 12. The buffalo in 5d CIDR-Heatsynch had greater (p < .05) E2 concentrations, estrus induction and increasing trend (p < .08) for conception rate (57.7% vs. 43.6%) than 5d CIDR-Cosynch. The percentage of pregnant buffalo that exhibited estrus signs was greater (p < .01) in 5d CIDR-Heatsynch than 5d CIDR-Cosynch. Positive correlation (p < .01) was observed between POF and E2 concentrations; POF and CL diameter, CL diameter and P4 concentrations. Estrus response and P4 concentrations were indicators of probability of pregnancy. In conclusion, 5d CIDR-Heatsynch tended to improve conception rate. The estrus expression and P4 concentrations (d5 and 12 post-first-AI) is the indicator of probability of pregnancy in buffalo.

Paternal determinants of early embryo development

Existing research has primarily focused on investigating the impacts of the maternal environment, female fertility phenotype, and genetics on pregnancy loss in dairy cattle. Recently, attention has been directed toward understanding the role the sire has on embryo quality and viability. Studies have shown there is a paternal influence on early pregnancy loss, but the specific mechanisms impacting pregnancy establishment and maintenance remain unclear. Despite clear differences that sires have on pregnancy outcomes, there is a lack of evidence regarding specifically how sires influence pregnancy. Sperm characteristics, such as motility, concentration, and morphology, have been extensively studied, but further research is needed to understand what makes one sire more or less fertile than another sire and how this affects pregnancy. To effectively address pregnancy loss, a deeper understanding of the processes involved from fertilisation to blastocyst formation is essential, particularly for understanding early pregnancy loss.

Uterine Fluid Extracellular Vesicles Proteome Is Altered During the Estrous Cycle

Uterine environment is tightly and finely regulated via various signaling pathways mediated through endocrine, exocrine, autocrine, juxtacrine, and paracrine mechanisms. In utero signaling processes are paramount for normal and abnormal physiology which involves cell to cell, cells to gametes, cells to embryo, and even interkingdom communications due to presence of uterine microbiota. Extracellular vesicles (EVs) in the uterine fluid (UF) and their cargo components are known to be mediators of in utero signaling and communications. Interestingly, the changes in UF-EV proteome during the bovine estrous cycle and the effects of these differentially enriched proteins on embryo development are yet to be fully discovered. In this study, shotgun quantitative proteomics-based mass spectrometry was employed to compare UF-EV proteomes at day 0, 7, and 16 of the estrous cycle to understand the estrous cycle-dependent dynamics. Furthermore, different phase UF-EVs were supplemented in embryo cultures to evaluate their impact on embryo development. One hundred fifty-nine UF-EV proteins were differentially enriched at different time points indicating the UF-EV proteome is cycle-dependent. Overall, many identified pathways are important for normal uterine functions, early embryo development, and its nutritional needs, such as antioxidant activity, cell morphology and cycle, cellular homeostasis, cell adhesion, and carbohydrate metabolic process. Furthermore, the luteal phase UF-EVs supplementation increased in vitro blastocyst rates from 25.0 ± 5.9% to 41.0 ± 4.0% (p ≤ 0.05). Our findings highlight the importance of bovine UF-EV in uterine communications throughout the estrous cycle. Interestingly, comparison of hormone-synchronized EV proteomes to natural cycle UF-EVs indicated shift of signaling. Finally, UF-EVs can be used to improve embryo production in vitro.

The microbiota of uterine biopsies, cytobrush and vaginal swabs at artificial insemination in Norwegian red cows

The individual resistance or tolerance against uterine disease in dairy cattle might be related to variations in the uterine tract microbiota. The uterine tract microbiota in dairy cattle is a field of increasing interest. However, its specific taxonomy and functional aspects is under-explored, and information about the microbiota in the endometrium at artificial insemination (AI) is still missing. Although uterine bacteria are likely to be introduced via the vaginal route, it has also been suggested that pathogens can be transferred to the uterus via a hematogenous route. Thus, the microbiota in different layers of the uterine wall may differ. Norwegian Red (NR) is a high fertility breed that also has a high prevalence of subclinical endometritis (SCE), an inflammation of the uterus that has a negative effect on dairy cattle fertility. However, in this breed the negative effect is only moderate, raising the question of whether this may be due to a favorable microbiota. In the present study we investigated the endometrial microbiota in NR at AI by biopsy and cytobrush samples, and comparing this to the vaginal microflora. The second objective was to describe potential differences at both distinct depths of the endometrium, in healthy vs SCE positive NR cows. We sampled 24 lactating and clinically healthy Norwegian red cows in their second heat or more after calving, presented for first AI. First, we obtained a vaginal swab and a cytobrush sample, in addition to a cytotape to investigate the animal's uterine health status with respect to SCE. Secondly, we acquired a biopsy sample from the uterine endometrium. Bacterial DNA from the 16S rRNA gene was extracted and sequenced with Illumina sequencing of the V3-V4 region. Alpha and beta diversity and taxonomic composition was investigated. Our results showed that the microbiota of endometrial biopsies was qualitatively different and more even than that of cytobrush and vaginal swab samples. The cytobrush samples and the vaginal swabs shared a similar taxonomic composition, suggesting that vaginal swabs may suffice to sample the surface-layer uterine microbiota at estrus. The current study gave a description of the microbiota in the healthy and SCE positive NR cows at AI. Our results are valuable as we continue to explore the mechanisms for high fertility in NR, and possible further improvements.

Insulin-like growth factor (IGF) performance in ovarian function and applications in reproductive biotechnologies

The role of the insulin-like growth factor (IGF) system has attracted close attention. The activity of IGF binding proteins (IGFBPs) within the ovary has not been fully elucidated to date. These proteins bind to IGF with an equal, or greater, affinity than to the IGF1 receptor, thus being in the main position to regulate IGF signalling, in addition to extending the half-life of IGFs within the bloodstream and promoting IGF storage in specific tissue niches. IGF1 has an important part in cell proliferation, differentiation and apoptosis. Considering the importance of IGFs in oocyte maturation, this review sought to elucidate aspects including: IGF production mechanisms; constituent members of their family and their respective functions; the role that these factors play during folliculogenesis, together with their functions during oocyte maturation and apoptosis, and their performance during luteal development. This review also explores the role of IGFs in biotechnological applications, focusing specifically on animal genetic gain.

β-Hydroxybutyrate Effects on Bovine Caruncular Epithelial Cells: A Model for Investigating the Peri-Implantation Period Disruption in Ketotic Dairy Cows

Ketosis is a metabolic disorder arising from a negative energy balance (NEB). It is characterized by high β-Hydroxybutyrate (BHBA) blood levels and associated with reduced fertility in dairy cows. To investigate the impact of BHBA on bovine caruncular epithelial cells (BCEC) in vitro, these cells were stimulated with different concentrations of BHBA. Cell metabolism and motility were examined using an MTT assay and Live-cell imaging. RT-qPCR was used to examine mRNA expressions of TNF, IL6, RELA, prostaglandin E2 synthase (PTGES2) and receptor (PTGER2) as well as integrin subunits ITGAV, ITGA6, ITGB1 and ITGB3. Stimulation with 1.8 and 2.4 mM of BHBA negatively affected cell metabolism and motility. TNF showed increased mRNA expression related to rising BHBA concentrations. IL6, RELA, ITGAV, ITGA6, ITGB1 and ITGB3 as well as PTGER2 showed no changes in mRNA expression. Stimulation with 0.6 and 1.2 mM of BHBA significantly increased the mRNA expression of PTGES2. This does not indicate a negative effect on reproductive performance because low BHBA concentrations are found in steady-state conditions. However, the results of the study show negative effects of high BHBA concentrations on the function of BCECs as well as an inflammatory response. This could negatively affect the feto-maternal communication during the peri-implantation period in ketotic dairy cows.

Oxidative activity of corpus luteum and ovarian parenchyma in Bos taurus indicus heifers

The aim of this study was to evaluate the oxidative stress in ovaries and corpus luteum (CL) of Bos taurus indicus females and the oxidant effect of CL in ovarian tissues in regions near, intermediate, or distant from it. Ovaries (n=12) of Nelore heifers (n=6) were collected from a slaughterhouse and fragmented. Experiment 1, each ovary was obtained from three fragments, resulting in 18 fragments of ovaries with CL (OV+CL) and another 18 fragments of ovaries without CL (OV-CL). Three fragments were generated from CL, totaling 18 CL fragments. In experiment 2, the ovarian fragments were removed from specific regions near, intermediate, or distant from the CL. All the fragments were placed in Eppendorf-type microtubes (1 mL), kept in a thermal container at 4 ºC, and then stored in a -80 ºC freezer for analysis of oxidative stress (TBARS and NBT) and antioxidant potential (FRAP and ABTS). In the antioxidant activity analysis, luteal tissues showed more antioxidant activity than ovarian tissue (FRAP = P < 0.0001; ABTS = P < 0.02). In the oxidative stress analysis, CL had lower levels of reactive oxygen species (ROS; TBARS = P < 0.03; NBT = P < 0.0001) than ovarian tissues. There was no difference in antioxidant activity and oxidative stress between the fragments obtained from different regions (OV+CL versus OV-CL; P > 0.05). The presence of CL in the ovaries of Bos taurus indicus females did not influence the oxidative stress or antioxidant potential of the gonad. Thus, the removal of ovarian fragments with or without the presence of CL indicates that biotechnologies such as in vitro follicle cultivation is possible.

Single-cell transcriptomic characterization of sheep conceptus elongation and implantation

Bidirectional communication between the developing conceptus and endometrium is essential for pregnancy recognition and establishment in ruminants. We dissect the transcriptomic dynamics of sheep conceptus and corresponding endometrium at pre- and peri-implantation stages using single-cell RNA sequencing. Spherical blastocysts contain five cell types, with 68.62% trophectoderm cells. Strikingly, elongated conceptuses differentiate into 17 cell types, indicating dramatic cell fate specifications. Cell-type-specific gene expression delineates the features of distinctive trophectoderm lineages and indicates that the transition from polar trophectoderm to trophoblast increases interferon-tau expression and likely drives elongation initiation. We identify 13 endometrium-derived cell types and elucidate their molecular responses to conceptus development. Integrated analyses uncover multiple paired transcripts mediating the dialogues between extraembryonic membrane and endometrium, including IGF2-IGF1R, FGF19-FGFR1, NPY-NPY1R, PROS1-AXL, and ADGRE5-CD55. These data provide insight into the molecular regulation of conceptus elongation and represent a valuable resource for functional investigations of pre- and peri-implantation ruminant development.

The interaction between the environment and embryo development in assisted reproduction

It can be assumed that the natural processes of selection and developmental condition in the animal provide the best prerequisites for embryogenesis resulting in pregnancy and subsequent birth of a healthy neonate. In contrast, circumventing the natural selection mechanisms and all developmental conditions in a healthy animal harbors the risk of counteracting, preventing or reducing the formation of embryos or substantially restricting their genesis. Considering these facts, it seems to be obvious that assisted reproductive techniques focusing on early embryonic stages serve an expanded and unselected germ cell pool of oocytes and sperm cells, and include the culture of embryos outside their natural habitat during and after fertilization for manipulation and diagnostic purposes, and for storage. A significant influence on the early embryonic development is seen in the extracorporeal culture of bovine embryos (in vitro) or stress on the animal organism (in vivo). The in vitro production per se and metabolic as well as endocrine changes in the natural environment of embryos represent adequate models and serve for a better understanding. The purpose of this review is to give a brief presentation of recent techniques aimed at focusing more on the complex processes in the Fallopian tube to contrast in vivo and in vitro prerequisites and abnormalities in early embryonic development and serve to identify potential new ways to make the use of ARTs more feasible.

Stimulation of Estrus and Ovulation by Resynchronization in Kangal Sheep during Early Anestrus

A total of 100 Kangal sheep were divided into four groups with the aim of investigating the effectiveness of resynchronization during anestrus for the first time in the literature. The groups were then divided into two further subgroups, namely the resynchronization subgroup group (hCG+resynch) and group (resynch)) and the no resynchronization subgroup (Group (hCG) and group (control)). All the groups started with progesterone-containing sponge insertion on Day 7. The sponge was removed after 7 days (on Day 0), and 600 IU eCG + 131.5 µg PGF2α was injected. The animals in group (hCG+resynch) and group (hCG) received hCG injection at the time of sponge administration. Accordingly, four different groups were established, i.e., resynchronization + hCG administration group (hCG+resynch); n:25), no resynchronization + hCG administration (group (hCG); n:25), resynchronization + no hCG administration (group (resynch); n:25), and no resynchronization + no hCG administration (Group (control); n:25). Estrus rates at the first application in group (hCG+resynch), group (hCG), group (resynch), and group (control) groups were 76%, 88%, 96%, and 76%, respectively, and pregnancy rates were 52%, 64%, 72%, and 60%, respectively; there were no intergroup statistical differences in the two parameters above. It was concluded that resynchronization performed with two consecutive stimulations during anestrus could help save time and provide a pregnancy rate at a level that can provide economic returns.

[Sonographic studies on the significance of follicle size and corpus luteum morphology in dairy cows after insemination]

OBJECTIVE

In dairy cattle, numerous factors determine the success of an insemination. The aim of the present study was to generate findings concerning the association between the preovulatory follicles, the corpora lutea with or without cavities and pregnancy in dairy cows under field conditions.

MATERIAL AND METHODS

Data was obtained from 176 dairy cows scheduled for artificial insemination. The cows were gynecologically examined using sonography at the time of insemination, 24 hours later, on day 9, on day 34 and after day 42 after insemination. Additionally, blood samples were collected from the coccygeal vein at the time of insemination and on day 9 in order to determine blood progesterone level.

RESULTS

Depending on the result of the pregnancy test, no difference was detected between the dimensions of the follicles, corpora lutea as well as their cavities and progesterone levels 9 days after insemination in the dairy cows with spontaneous ovulations. In contrast to the corpus luteum without cavity, the surface area of the corpus luteum with cavity remained constant during the study period, while at the same time the cavity decreased in size to a significant degree. In addition, breed differences in corpus luteum sizes were detected on day 34.

CONCLUSION

No cause was detected for the formation of cavities in corpora lutea and there was no link to the follicle from which the corpus luteum developed.

CLINICAL RELEVANCE

Both the changes in corpus luteum sizes over time and their breed-related differences could have an impact on insemination outcome.

Effects of postpartum diseases on antral follicle count and serum concentration of Anti-Müllerian hormone in dairy cows

The antral follicle count (AFC) and Anti-Müllerian hormone (AMH) concentration are validated markers for ovarian reserve in cattle, but their use as fertility markers is controverse. Here we assessed the effects of postpartum diseases on AFC and AMH concentration, as well as the influence of parity and breed on these parameters. Cows (n = 513, mostly Holstein Friesian and Brown Swiss, parity 3.0 ± 1.8) underwent a single ultrasonography examination 28-56 days after parturition and categorized as having low (n ≤ 15 follicles), intermediate (n = 16-24 follicles), or high (n ≥ 25 follicles) AFC based on objective video analysis of recorded sequences. Blood samples for AMH determination were collected at the time of examination and animals divided into low (< 0.05 ng/ml) and high AMH (≥ 0.05 ng/ml) group, respectively. No effects of postpartum diseases or breed on either AFC or AMH groups could be observed. There was a strong interaction between parity and AFC, primiparous cows having less follicles (13.6 ± 6.2 vs. 17.1 ± 7.0, P < 0.001) than pluriparous cows. The AFC did not affect reproductive parameters or productivity of the cows. In comparison, pluriparous cows with high AMH concentration had shorter calving to first service (86.0 ± 37.6 vs. 97.1 ± 46.7 days, P < 0.05) and calving to conception (123.8 ± 51.9 vs. 135.8 ± 54.4 days, P < 0.05) intervals, but lower milk yield (8440.3 ± 2292.9 vs. 8927.9 ± 2192.5 kg, P < 0.05) compared to cows with low AMH. In conclusion, no effect of postpartum diseases on AFC or AMH concentration of dairy cows could be observed. However, an interaction between parity and AFC, as well as associations of AMH with fertility and productivity in pluriparous cows, were demonstrated.

Review: The ovarian follicular reserve - implications for fertility in ruminants

Ruminants are born with a finite number of healthy ovarian follicles and oocytes (ovarian reserve) and germ cell proliferation in the developing foetal gonad predominantly occurs during early gestation. Two markers have been established to reliably estimate the size of the ovarian reserve in cattle: the number of antral follicles ≤3 mm in diameter recruited per follicular wave (Antral Follicle Count, AFC) and peripheral concentrations of the Anti-Müllerian hormone (AMH). Studies that used one or both indicators show that the size of ovarian reserve varies greatly among age-matched individuals, but is highly repeatable in the same animal. Conditions during prenatal life are likely among the causes of such variation in the ovarian reserve. In addition, the size of the ovarian reserve is a moderately heritable trait in cattle. The association between ovarian reserve and fertility is controversial. Several studies indicate that cattle with a low ovarian reserve have phenotypic characteristics that are associated with suboptimal fertility. On the contrary, the presence and absence of a positive association between AFC and/or AMH and fertility measures (i.e. no. on services/conception, pregnancy rates, pregnancy loss) have been equally reported in cattle. In conclusion, the size of the ovarian reserve in the progeny can be enhanced by improving management of the dam from preconception to early gestation and also through genetic selection. However, although the ovarian reserve may be among the determinants of reproductive success in ruminants, the use of AFC/AMH as reliable predictors of fertility is yet to be established. Furthermore, the possibility that there is a complex interaction of AFC, AMH and reproduction has yet to be fully characterised and exploited to improve fertility in cattle.

Review: Endometrial function in pregnancy establishment in cattle

The endometrium is fundamentally required for successful pregnancy in ruminants and species where the posthatching conceptus undergoes a protracted elongation and peri-implantation phase of pregnancy. Moreover, there are substantial waves of pregnancy loss during this pre- and peri-implantation period of pregnancy the precise source of which has not been clearly defined i.e., the maternal uterine contribution to this loss. Understanding the molecular interactions required for successful pregnancy in cattle will allow us to intervene to support pregnancy success during this vulnerable window. The endometrium contributes to most key developmental milestones of pregnancy establishment, including (1) contributing to the regulation of the oestrus cycle, (2) nourishing the preimplantation conceptus, (3) responding to the conceptus to create a more receptive microenvironment, (4) providing essential biophysical support, and (5) signalling and producing factors which affect the mother systemically. This review will summarise what we currently know about conceptus-maternal interactions as well as identify the gaps in our knowledge that could be filled with newer in vitro model approaches. These include the use of microfluidics, organ-on-a-chip devices, and bioinformatic approaches. This will help maximise food production efficiency (both meat and dairy) and decrease the environmental burden, while enhancing our understanding of the fundamental processes required for successful implantation in cattle.

Pre-hatching exposure to N2B27 medium improves post-hatching development of bovine embryos in vitro

Ungulate embryos undergo critical cell differentiation and proliferation events around and after blastocyst hatching. Failures in these processes lead to early pregnancy losses, which generate an important economic impact on farming. Conventional embryo culture media, such as SOF, are unable to support embryo development beyond hatching. In contrast, N2B27 medium supports early post-hatching development, evidencing a swift in embryonic nutritional requirements during this developmental window. Here, we investigate if earlier exposure to N2B27 could improve embryo development after hatching. Embryo culture in N2B27 from day (D) 5, 6 or 7 significantly enhanced complete hypoblast migration (>45 vs. ∼24%) and epiblast development into an embryonic disc (ED)-like structure at D12 (>40 vs. 23%), compared to embryos cultured in SOF up to D9. Culture in N2B27 from D5 significantly increased epiblast and hypoblast cell number in D8 blastocysts, but post-hatching embryos cultured in N2B27 from D5 or 6 frequently showed a disorganized distribution of epiblast cells. In conclusion, bovine embryo culture in N2B27 from D7 onwards improves subsequent post-hatching development. This improved fully in vitro system will be very useful to functionally explore cell differentiation mechanisms and the bases of early pregnancy failures without requiring animal experimentation.

Deterioration of mitochondrial biogenesis and degradation in the endometrium is a cause of subfertility in cows

To investigate possible causes of reproductive failure, we conducted global endometrial gene expression analyses in fertile and subfertile cows. Ingenuity pathway analysis showed that RICTOR and SIRT3 are significant upstream regulators for highly expressed genes in fertile cows, and are predicted to be activated upstream regulators of normal mitochondrial respiration. Canonical pathway analysis revealed that these highly expressed genes are involved in the activation of mitochondrial oxidative phosphorylation. Therefore, in subfertile cows, the inactivation of RICTOR and SIRT3 may correlate with decreased capacity of mitochondrial respiration. Furthermore, the expression levels of most mitochondrial DNA genes and nuclear genes encoding mitochondrial proteins were higher in subfertile cows. The mitochondrial DNA copy number was significantly higher in the endometrium of subfertile cows, whereas the ATP content did not differ between fertile and subfertile cows. Quantitative reverse transcription-PCR analysis demonstrated that the expression of PGC1a, TFAM, MFN1, FIS1, and BCL2L13 were significantly lower in subfertile cows. In addition, transmission electron microscopy images showed mitochondrial swelling in the endometrial cells of the subfertile cow. These results suggest that poor-quality mitochondria accumulate in the endometrium owing to a reduced capacity for mitochondrial biogenesis, fusion, fission, and degradation in subfertile cows, and may contribute to infertility.

Expression profile of genes related to pregnancy maintenance in Dromedary Camel during the first trimester

So far, few signals involved in embryo-maternal dialogue have been identified in pregnant she-camel. Our objective was to investigate expression profiles of genes relevant to uterine extracellular matrix remodeling (ITGB4, SLCO2A1, FOS, and JUN), uterine tissue vascularization, and placental formation (VEGFA, PGF, and PDGFA), embryonic growth and development (IGF1 and PTEN), plus cell death of uterine tissue (BCL2) in early pregnant versus non-pregnant she-camels. Forty genital tracts (20 pregnant and 20 non-pregnant) and blood samples were collected from abattoirs. Total RNA was extracted from uterine tissues and qRT-PCR was conducted for candidate genes. Serum concentrations of progesterone (P4) and estradiol17-β (E2) were measured. Expression of ITGB4, FOS, and PGF genes increased (P < 0.001) in the right uterine horn of pregnant versus non-pregnant she-camels. Moreover, JUN, SLCO2A1, VEGFA, and PTEN mRNAs were up-regulated (P < 0.001) in various segments of uterine tissues in pregnant groups. The PDGFA transcript was over-expressed (P < 0.001) in both uterine horns of pregnant groups. Additionally, IGF1 was higher (P < 0.001) in the right horn and the uterine body of pregnant groups, and expression of BCL2 was increased (P < 0.001) in the pregnant uterine body. Moreover, serum concentrations of P4 were higher (P < 0.001) and E2 lower (P < 0.05) in pregnant she-camels. Taken together, the fine-tuning of genes related to implantation, matrix formation, vascularization, and placental formation is highly required for successful pregnancy in she-camels.

Machine-learning methods applied to integrated transcriptomic data from bovine blastocysts and elongating conceptuses to identify genes predictive of embryonic competence

Early pregnancy loss markedly impacts reproductive efficiency in cattle. The objectives were to model a biologically relevant gene signature predicting embryonic competence for survival after integrating transcriptomic data from blastocysts and elongating conceptuses with different developmental capacities and to validate the potential biomarkers with independent embryonic data sets through the application of machine-learning algorithms. First, two data sets from in vivo-produced blastocysts competent or not to sustain a pregnancy were integrated with a data set from long and short day-15 conceptuses. A statistical contrast determined differentially expressed genes (DEG) increasing in expression from a competent blastocyst to a long conceptus and vice versa; these were enriched for KEGG pathways related to glycolysis/gluconeogenesis and RNA processing, respectively. Next, the most discriminative DEG between blastocysts that resulted or did not in pregnancy were selected by linear discriminant analysis. These eight putative biomarker genes were validated by modeling their expression in competent or noncompetent blastocysts through Bayesian logistic regression or neural networks and predicting embryo developmental fate in four external data sets consisting of in vitro-produced blastocysts (i) competent or not, or (ii) exposed or not to detrimental conditions during culture, and elongated conceptuses (iii) of different length, or (iv) developed in the uteri of high- or subfertile heifers. Predictions for each data set were more than 85% accurate, suggesting that these genes play a key role in embryo development and pregnancy establishment. In conclusion, this study integrated transcriptomic data from seven independent experiments to identify a small set of genes capable of predicting embryonic competence for survival.

Oocyte developmental capacity is influenced by intrinsic ovarian factors in a bovine model for individual embryo production

The ovary and its hormones may have major effects on the in vitro developmental capacity of the oocytes it contains. We related intrinsic ovarian factors namely the presence of corpus luteum (CL) and/or dominant follicle (>8 mm) and the follicular count to cumulus expansion (CE), embryo development, and blastocyst quality in a bovine model. Cumulus-oocyte-complexes (COCs) were aspirated from follicles between 4 and 8 mm in diameter. In vitro embryo production was performed in a fully individual production system. The follicular fluid from which COCs were collected was pooled (per ovary) to evaluate the estrogen, progesterone, and insulin-like growth factor-1 (IGF-1) concentrations. Cumulus oocyte complexes collected from ovaries without a CL presented a greater CE than COCs derived from ovaries bearing CL. The absence of ovarian structures increased the blastocyst rate when compared to oocytes derived from ovaries with a CL, a dominant follicle, or both. Blastocysts derived from ovaries without a dominant follicle presented higher total cell numbers and a lower proportion of apoptosis than blastocysts derived from ovaries containing a dominant follicle. Cumulus oocyte complexes collected from ovaries with high follicular count resulted in higher cleavage than from ovaries with low follicular count, but the blastocyst rate was similar between groups. Ovaries bearing a CL had greater progesterone and IGF-1 follicular fluid concentrations in neighboring follicles than ovaries without a CL. Selection for bovine ovaries without CL or dominant follicle can have positive effects on CE, embryo development, and blastocyst quality in an individual embryo production system set-up.

Relationship between ovarian ultrasonographic findings on the seventh post-estrus day and plasma progesterone concentration, nutritional metabolic factors, and pregnancy outcome in dairy cows

To improve the accuracy of ultrasonographic assessment of luteal function, we investigated the relationship between ovarian ultrasonographic findings on Day 7 (Day 1 = ovulation) and plasma progesterone (P₄) concentration, nutritional metabolic factors, and pregnancy outcome. A total of 47 spontaneous estrus events were investigated in 38 lactating Holstein cows (artificial insemination, n = 31; embryo transfer, n = 16). Transrectal ultrasonography was performed on Days 0 and 7 to measure the pre-ovulatory follicle area on Day 0 and the luteal tissue area (LTA), luteal blood flow area (LBF), relative LBF (rLBF) (= LBF/LTA), and dominant follicle area (DFA) on Day 7. Blood samples were collected on Day 7 to measure plasma P₄, insulin-like growth factor-I (IGF-I), insulin, and metabolites. Plasma P₄ concentration was positively correlated with LTA but was not associated with LBF or rLBF. Plasma P₄ concentration was positively correlated with blood glucose and IGF-I and negatively correlated with blood urea nitrogen and free fatty acid, and no significant relationship was found between the ultrasonographic findings of the corpus luteum (CL) and these blood metabolites. Pregnant cows had smaller DFA than non-pregnant cows. In conclusion, LTA measurement can help predict plasma P₄ concentration, but it was difficult to detect variations in plasma P₄ concentration in relation to changes in energy status by evaluating the CL ultrasonographically. A combined assessment of CL and first-wave dominant follicle may be important in evaluating fertility.

Pregnancy and parturition in dromedary camels III. Incidence, timing and factors affecting abortions and perinatal mortality under intensive management

In this study, the incidence, timing and risk factors associated with abortion and perinatal mortality (PM) were described in dromedary camels under intensive management. In addition, overall pregnancy losses were also summarized and weekly risk of pregnancy wastage was determined throughout gestation. Data were collected over 11 breeding seasons from September 2006 through June 2017 at the world's largest camel dairy farm. A total of 229 abortions were observed (5.05%) out of 4533 pregnancies after 60 days (d) of gestation. Most abortions were singleton (n = 199, 86.9%), but twin abortions were also recorded in 30 cases (13.1%). Abortions showed a pronounced seasonal distribution, with a peak in August. The age category (P < 0.01), breed or ecotype of the female (P < 0.05) and bull influenced the occurrence of singleton abortions. Dromedaries with twins tended to abort earlier than those with a singleton fetus (median = 232.5 d vs. 257 d, P = 0.053). Perinatal mortality was observed in 174 cases (3.84%) out of 4533 pregnancies after 60 d of gestation. The condition included the premature birth of non-viable calves after shorter than normal gestation (330-350 d, n = 26, 14.9%), the birth of well-developed but dead calves after normal gestation length (n = 120, 69.0%) and neonates that died within 48 h after delivery (n = 28, 16.1%). The frequency distribution of PM was parallel with that of parturitions. The most important predisposing factor for PM was difficult calving. Thirty-nine percent (68 out of 174) of these losses were associated with dystocia. In addition, age category (P < 0.05) and parity of the female (P < 0.01), month of delivery (P < 0.05) and breeding season (P < 0.05) also affected the incidence of PM. The cause of 60 cases of PM (1.4% of all deliveries) could not be determined and was considered idiopathic. In conclusion, one-third of total pregnancy losses occurred during mid to late gestation. Approximately 10% of pregnancies after Day 60 failed, and 90% resulted in the birth of a live calf that survived beyond 48 h. More than half of these pregnancy losses were abortions before 330 d of gestation, and approximately 40% were classified as PM. The weekly mean risk of pregnancy loss after 100 d of gestation remained only a fraction of that observed during the first 2-3 months.

What are the factors associated with pregnancy loss after timed-artificial insemination in Bos indicus cattle?

Pregnancy loss (PL) has important impacts on the profitability of livestock production systems, although it is not widely reported, particularly in Bos indicus cattle. The present study retrospectively evaluated PL after timed-artificial insemination (TAI) in Bos indicus (Nelore) beef cows corresponding to several factors, such as parity, body condition score (BCS), presence of corpus luteum (CL) at the beginning of TAI protocols, expression of estrus, and hormonal manipulations during the TAI protocol. Data from two experiments performed during three breeding seasons (BS) were reanalyzed. Both experiments evaluated adding GnRH treatment at TAI in a 7-d estradiol (E2) plus progesterone (P4)-based protocol, with intravaginal P4 implant removal on Day 7 combined with treatment with 0.5 or 1.0 mg E2 cypionate and 300 IU eCG, and TAI on Day 9. In addition, during BS 2 and 3 (Exp 2), cows were randomized to receive or not a PGF treatment on Day 0 (beginning of the TAI protocol). In all BS, presence of CL and BCS were evaluated at the beginning of TAI protocols, follicle size and expression of estrus were evaluated at TAI. The PL was assessed between the first pregnancy diagnosis (∼35d) and parturition. There were no effects of hormonal manipulations within TAI protocols of different BS on PL. There was no interaction between GnRH treatment at TAI and the other variables within BS, and there was no main effect of GnRH treatment on PL (without = 10.1% [102/1007] vs. with = 10.4% [114/1100]). The addition of PGF on Day 0 had no effect on PL (11.5% [102/886] vs. 10.5% [89/850]), as well as EC dose to induce final ovulation (10.8% [89/827] vs. 11.2% [102/909] for 0.5 and 1.0 mg, respectively). Primiparous had greater PL than multiparous cows (14.0% [77/550] vs. 8.9% [139/1557]), and cows not expressing estrus near TAI had greater PL than those expressing estrus (13.5% [57/422] vs. 9.7% [156/1617]). There was no interaction between follicle size at TAI and GnRH treatment on PL. However, probability of PL decreased linearly as follicle size at TAI increased. There were no effects of service number (first TAI or resynchronization), BCS, or presence of CL on D0 on PL. In addition, PL was not affected by sire within any of the BS. In conclusion, some factors that are known to impact pregnancy per AI also influenced PL, such as parity and expression of estrus, although, other aspects such as BCS, number of services, and presence of CL on D0 did not affect PL. Moreover, commonly implemented treatments to increase fertility (e.g., PGF on Day 0 and increasing EC dose to 1.0 mg) did not affect PL. Finally, the GnRH treatment at TAI had no effect on PL and did not interact with any of the variables, an important result, since GnRH at TAI also increases fertility in Bos indicus beef cows.

Transforming growth factor beta (TGFβ) pathway is essential for hypoblast and epiblast development in ovine post-hatching embryos

The developmental failures occurring between blastocyst hatching and implantation in farm ungulates are a major cause of pregnancy losses. At the expanded blastocyst stage, three cell lineages emerge in the embryo: trophoblast, hypoblast and epiblast, the latter being the most vulnerable during post-hatching development. Transforming growth factor beta (TGFβ) signaling pathway is involved in hypoblast and epiblast development; however, previous in vitro functional studies are limited to the expanded blastocyst stage. In this study, we have analyzed the effect of TGFβ inhibition with 10, 20 or 40 μM SB431542 during ovine post-hatching developmental period using a recently developed culture system able to recapitulate major developmental landmarks. We have found a negative effect of TGFβ inhibition on hypoblast and epiblast development that could be partially reverted by Rho-associated protein kinase (ROCK) inhibitor Y-27632. Our findings provide new insights into the molecular networks regulating embryo development beyond the expanded blastocyst and could help to elucidate the causes of early pregnancy losses in farm ungulates.

Phosphate, calcium, and vitamin D signaling, transport, and metabolism in the endometria of cyclic ewes

BACKGROUND

Recent evidence suggests important roles for progesterone (P4) and interferon tau in the regulation of calcium, phosphate, and vitamin D signaling in the uteri of pregnant sheep. However, the effects of P4 and estradiol (E2), with respect to the expression of their receptors PGR and ESR1, respectively, in uterine epithelia on mineral signaling during the estrous cycle has not been investigated. Estrous cycles of mature Suffolk ewes were synchronized, prostaglandin F2α was administered, and ewes were observed for estrus (designated as Day 0) in the presence of vasectomized rams. On Days 1, 9, or 14 of the estrous cycle, hysterectomies were performed.

RESULTS

25-hydroxyvitamin D was more abundant in plasma from ewes on Day 14 than Day 1 (P < 0.05). Expression of fibroblast growth factor receptor 2 (FGFR2), a disintegrin and metalloprotease 17 (ADAM17), and parathyroid hormone-related protein (PTHrP) mRNAs was greater in endometria on Day 9 compared to Days 1 and 14 (P < 0.01). Similarly, expression of transient receptor potential cation channel subfamily V member 6 (TRPV6) mRNA was greater in endometria on Day 9 than Day 1 (P < 0.05). ATPase plasma membrane Ca²⁺ transporting 4 (ATP2B4) and S100 calcium binding protein G (S100G) mRNA expression was greater in endometria on Day 14 than on Days 1 and 9 (P < 0.01). In contrast, endometrial expression of vitamin D receptor (VDR) mRNA was lower on Days 9 and 14 than Day 1 (P < 0.01). Expression of klotho (KL) (P < 0.05) and cytochrome P450 family 24 subfamily A member 1 (CYP24) (P < 0.01) mRNAs was lower on Day 14 than Days 1 and 9. ADAM17, FGF23, CYP2R1, CYP27B1, KL, and VDR proteins immunolocalized to the uterine myometrium, blood vessels, and uterine luminal (LE), superficial glandular (sGE), and glandular (GE) epithelia. S100A9 protein was weakly expressed in the uterine myometrium, LE, sGE, and GE. Immunoreactivity of CYP2R1 and KL proteins in uterine LE and sGE was less on Day 1 than on Days 9 and 14. In contrast, S100G protein was expressed exclusively by GE, and immunoreactive S100G protein was less on Day 9. S100A12 protein localized to stromal cells of the uterine stratum spongiosum and blood vessels, but not by uterine epithelial cells.

CONCLUSION

Collectively, these results implicate E2, P4, and PGR in the regulation of phosphate, calcium, and vitamin D signaling in cyclic ewes.