Potential relationship between normalization of endometrial epidermal growth factor profile and restoration of fertility in repeat breeder cows

Changes in interleukin-2, -4, -6 and -8 expression in the postovulatory sow endometrium after artificial insemination based on conceived or failed to conceive

The establishment and maintenance of a pregnancy requires proper interaction between the endocrine and immune systems in the uterus. Therefore, it is crucial to understand how changes in endometrial cytokine levels facilitate reproduction. This study aimed to investigate how representative cytokines sequentially changed in the endometrium and whether conception could be attributed to these changes. In this study, artificial insemination was performed twice in 160 sows and ovulation was examined every 3 h using transrectal ultrasonography. Uterine endometrial tissues were obtained via repeated biopsies at 2, 4, 6, 8, 12, 16, and 20 h after ovulation and interleukin (IL)-2, IL-4, IL-6, and IL-8 expression was examined using real-time polymerase chain reaction. The conception rate was 91.9%. The IL-2 levels showed no differences in conception or time. The expression peaks of IL-4 and IL-6 were delayed in sows that failed to conceive within 4-6 h and 2 h, respectively, compared to those that did conceive. In sows that conceived, IL-8 was highest after 2 h, and no difference was observed at other time point, regardless of conception. In sows that failed to conceive, the increase in IL-8 levels might have been cancelled or terminated before the first sampling time. These results highlight the importance of timely increases and subsequent declines in the levels of some cytokines for the establishment of pregnancy. Differences in uterine capacity start just after ovulation; detection and correction of these deviations can improve the reproductive efficiency of sows.

Effects of recombinant osteopontin expressed in Escherichia coli on the recovery of the endometrial epidermal growth factor profile and fertility in repeat breeder dairy cows

Endometrial epidermal growth factor (EGF) shows a cyclic change with two peaks on days 2-4 and days 13-14 of the estrous cycle. In repeat breeder cows, loss of the peaks has been associated with reduced fertility. By infusing seminal plasma (SP) and osteopontin (OPN) derived from SP and milk into the vagina, their EGF profile and fertility are restored. However, SP is difficult to obtain, and both SP and OPN can transmit infectious diseases. While OPN can be sourced from recombinant protein without this risk, recombinant bovine OPN (rOPN) expressed in Escherichia coli should be examined for its effects on the EGF profile, since it does not undergo posttranslational modification, which is important for its biological activity. In study 1, PBS, SP (0.5 mL), and rOPN (0.3 mg) were infused into the vagina at estrus (day 0) in 74, 37, and 105 repeat breeder Holstein cows, respectively, with an altered EGF profile. The endometrial EGF concentrations were measured on day 3. Some cows (n = 58, 20, and 83, respectively) were inseminated immediately before the infusion and then diagnosed for pregnancy between days 30 and 35. The normalization rate of the EGF profile and conception rate in the rOPN group (58.1 % and 47.0 %, respectively) were not significantly different from those in the SP group (62.2 % and 45.0 %, respectively) but higher than those in PBS group (29.7 % and 28.1 %, respectively) (P < 0.05). In study 2, repeat breeder cows with an altered EGF profile were infused with PBS (n = 18) and rOPN (n = 17), while fertile controls with a normal EGF profile (n = 18) were infused with PBS. Two or three embryos were transferred into cows on day 7 and then recovered on day 14. Embryo recovery rates of the rOPN and fertile groups were comparable (58.7 % vs. 58.3 %) but higher than that of the PBS group (58.7 % vs. 32.0 %) (P < 0.05). The embryo recovery rate of cows with normalized EGF profile was higher than that of cows with unnormalized EGF profile (64.4 % vs. 16.7 %) (P < 0.05). The embryo sizes of cows in the rOPN and fertile groups were comparable but larger than those in the PBS group (P < 0.05). However, the embryo size was not correlated to the corresponding endometrial EGF concentrations. In conclusion, rOPN without posttranslational modifications normalized the EGF profile in repeat breeder cows. Improved fertility by normalization of the EGF profile could be attributed partly to the increased embryo viability up to day 14.

Equine chorionic gonadotropin treatment and timed artificial insemination for dairy cow production under heat stress

This study investigated the effects of timed artificial insemination (TAI) and equine chorionic gonadotropin (eCG) administration on lactating dairy cows under heat-stress conditions (average temperature-humidity index: 80). Timed artificial insemination was performed on the cows with (n = 57) or without (control, n = 41) supplementation with 500 IU of eCG at the day of PGF2α treatment using the CIDR-Ovsynch protocol. GnRH was administered, and a progesterone device (CIDR) was inserted on Day -10 of the treatment protocol. The CIDR was removed on Day -3, and the cows were treated with PGF2α. Two days later, a 2nd GnRH injection was administered. Subsequently, AI was performed on Day 0 (16-20 h after the 2nd GnRH injection), and pregnancy was diagnosed on Days 32 and 60. Plasma progesterone (P4) concentrations were measured after AI. Results showed that the eCG group had a higher pregnancy per AI (P/AI) than the control group (43.9 vs. 12.2%, P = 0.002), which was also accompanied by elevated P4 levels. Four cows in the eCG group had multiple calves, representing 7.0 and 16.0% of the group and pregnant cows, respectively. In conclusion, 500 IU of eCG combined with CIDR-Ovsynch in lactating dairy cows under severe heat stress conditions successfully improved fertility. However, the protocol may have a slight risk of multiple births.

Effects of prostaglandin F2α treatment at follicular wave emergence on endometrial epidermal growth factor concentration on day 3 of the next estrous cycle and on fertility in dairy cows

Inadequate exposure to estradiol (E2) and progesterone (P4) may be the main causes of altered endometrial epidermal growth factor (EGF) profile, leading to reduced fertility in dairy cows. We hypothesized that PGF2α administration at different timings of the estrous cycle and stages of follicular development could change the profile of steroid hormones between luteolysis and estrus. This results in reduction in the peak concentration of endometrial EGF on day 3 (day 0 = estrus) in the next estrous cycle. In study 1, lactating Holstein cows were treated with PGF2α either on days 12-14 (selection phase group, n = 20) or on days 16-17 (control group, n = 24) of the estrous cycle. Blood samples were obtained before PGF2α treatment, 24 and 48 h after treatment, and on the day of estrus and ovulation for E2 and P4 assays. Endometrial tissues were collected by biopsy on day 3 for EGF assays. The duration from PGF2α treatment to both estrus and ovulation was longer in the selection phase group than in the control group (P < 0.05). The time between estrus and ovulation was longer in the selection phase group (P < 0.05). E2 concentrations were higher in the control group on the day of estrus (P < 0.05). P4 concentrations were not different between the groups. Endometrial EGF concentrations were lower in the selection phase group than in the control group (P < 0.05). In study 2, lactating Holstein cows were treated with PGF2α either on day 12 (selection phase group, n = 76) or day 16 (control group, n = 80). They were subjected to artificial insemination (AI) at estrus, and those that failed to ovulate by 24h after the first AI were subjected to second AI. On day 3, endometrial EGF concentration was determined. At estrus and on days 3 and 7, blood was collected for E2 and P4 assay from 20 randomly selected cows in each group before PGF2α treatment. The cows in the selection phase group exhibited lower EGF concentration, proportion of cows with normal EGF profile, and conception rate than cows in the control group (P < 0.05). On the day of estrus, E2 concentrations tended to be lower in the selection phase group than in the control group (P = 0.08). P4 concentrations were not different between the groups. These findings suggest that low E2 concentrations at estrus and low P4 concentrations for a prolonged period due to premature termination of CL in the absence of a dominant follicle are potential causes of altered endometrial EGF profile in dairy cows.

Current Insights in the Repeat Breeder Cow Syndrome

Cows can have difficulties becoming pregnant, and in certain cases, these reproductive failures do not have an evident cause. Furthermore, when these failures are repeated three or more times with estrous cycles of normal duration and in the absence of evident clinical signs, it is considered repeat breeder cow (RBC) syndrome. A substantive incidence of RBC syndrome has been reported all over the world, which severely affects the farm economy. This paper reviews those studies particularly focused on RBC syndrome from 2000 to 2023 but also includes consolidated information until this date. Hormonal imbalances, undetectable oviductal or uterine defects, or poor oocyte or embryo quality have been reported as causes of RBC syndrome, while subclinical endometritis has been considered a relevant causal agent. However, it is unresolved why this condition is recurrent in certain animals, despite the implementation of corrective management actions or treatments. Recent studies evaluate the putative role of certain genes, factors, hormones, or proteins in the pathogenesis of RBC syndrome. Numerous risk factors contribute to the appearance of this syndrome, and some of them could be mitigated to partially prevent this infertility, while others cannot be changed. Due to the complexity of this syndrome, it is important to increase knowledge about the mechanisms involved, develop new diagnostic tools to differentiate causal agents, and implement new treatments to restore fertility. There is consensus about the huge repercussions of this syndrome on farm profitability, but further studies are now needed to describe its economic impact.

Effects of milk osteopontin on the endometrial epidermal growth factor profile and restoration of fertility in repeat breeder dairy cows

Endometrial epidermal growth factor (EGF) shows a cyclic change with two peaks on Days 2-4 and 13-14 during the estrous cycle. An altered (i.e., loss of the two peaks) profile has been linked to reduced fertility in repeat breeder cows. We previously demonstrated that a form of osteopontin (OPN), with a molecular weight of 29 kDa and found in bull seminal plasma (SP), normalized the EGF profile and restored fertility in repeat breeder cows. OPN has many molecular forms due to post-translational modifications and is abundant in bovine milk. The purpose of the present study was to investigate whether mOPN normalizes the endometrial EGF profile and restores fertility in repeat breeder dairy cows with an altered EGF profile. OPN was separated by one-step anion-exchange column chromatography from the whey of bovine milk. Purified mOPN was verified by Western blotting and peptide mass fingerprinting analyses. The OPN fraction showed three major protein bands of 61, 37 and 31 kDa (peptides I, II, and III, respectively) on SDS-PAGE. All three major bands were identified as OPNs by Western blotting and their tryptic peptide masses were matched at approximately 50, 40, and 10%, respectively, to the bovine OPN amino acid sequence by a peptide mass finger printing analysis. The three bands accounted for approximately 85% of the total protein content and 6-23 mg of OPN was obtained from 1 L of bovine milk. A lyophilized eluate containing 1.3 mg of mOPN (171 cows), 0.5 mL of frozen SP (62 cows), and PBS (84 cows) was infused at estrus into the vagina of repeat breeder cows with an altered EGF profile. Some of the cows treated with mOPN, SP, and PBS (46, 50, and 45 cows, respectively) were inseminated immediately before the infusion and then examined for pregnancy between Days 60 and 65. The rate at which mOPN to normalize the EGF profile (56.1%) was similar to that of SP (58.1%) and higher than that of PBS (23.8%) (P < 0.05). The conception rate after the infusion of mOPN (43.5%) was similar to that of SP (40.0%) and higher than that of PBS (22.2%) (P < 0.05). The present results indicate that the infusion of mOPN into the vagina is a treatment option for repeat breeder cows with an altered EGF profile. Further studies are needed to compare the capacity of the three OPN molecules in milk to normalize the EGF profile, together with their molecular characteristics due to post-translational modifications.

Leptin receptor expression and its change in association with the normalization of EGF profile after seminal plasma treatment in repeat breeder dairy cows

Factors associated with high milk production levels have been linked to alterations in the endometrial epidermal growth factor (EGF) profile, a cause of reduced fertility in dairy cows. Therefore, we examined the leptin system that connects nutritional status and reproduction in dairy cattle related to reduced fertility in repeat breeder cows. Plasma leptin concentrations were measured in 18 heifers, 20 high-yielding control cows, and 26 repeat breeder cows, showing an altered EGF profile. Then, all repeat breeder cows were infused with seminal plasma (SP) into the vagina at the next estrus to normalize the EGF profile, while heifers and control cows were infused with vehicle alone. All animals were examined for EGF profiles. Eighteen repeat breeder cows, nine heifers, and nine control cows were also determined for leptin receptor (Ob-R) expression levels in the estrous cycle before and after the infusion. SP normalized the EGF profile in 53.8% of the repeat breeder cows. Leptin concentrations were similar in all groups, regardless of the treatment results for the EGF profile. In contrast, Ob-R levels in repeat breeder and control cows were similar and higher than those in heifers before SP treatment. Ob-R in repeat breeders showing a normal EGF profile after treatment decreased to an intermediate level between heifers and control cows and may provide a clue to take measures against repeat breeding in dairy cows.

Effects of heat stress on the endometrial epidermal growth factor profile and fertility in dairy cows

The endometrial epidermal growth factor (EGF) profile is an indicator of uterine function and fertility in cattle. The present study aimed to investigate the effects of heat stress on the endometrial EGF profile and fertility in lactating Holstein cows. The endometrial EGF profiles of 365 cows in the Hokkaido and Kyushu regions were examined between June and September (heat stress period, n = 211) and between October and January (control period, n = 154). EGF profiles were investigated using uterine endometrial tissues obtained by biopsy 3 days after estrus (Day 3). The proportion of cows with an altered EGF profile was higher between June and September than between October and January (41.2 vs. 16.2%, P < 0.05). The effects of rectal temperature on Days 0 and 3 on the endometrial EGF profile were also assessed in cows (n = 79) between June and September in the Kyushu region. A single embryo was transferred to cow on Day 7 to evaluate fertility (n = 67). Regardless of the rectal temperature on Day 3, the proportion of cows with an altered EGF profile was higher (64.1 vs. 30.0%, P < 0.05) and the pregnancy rate after embryo transfer (ET) was lower (26.7 vs. 51.4%, P < 0.05) in cows with a rectal temperature ≥ 39.5°C on Day 0 than in cows with a rectal temperature < 39.5°C on Day 0. The present results indicate that alterations in the endometrial EGF profile induced by an elevated body temperature on Day 0 contributed to reductions in fertility in lactating dairy cows during the heat stress period.

Effect of Endometrial Sampling Procedures on Subsequent Pregnancy Rate of Cattle

Endometrial infections are a common cause of reproductive loss in cattle. Accurate diagnosis is important to reduce the economic losses caused by endometritis. A range of sampling procedures have been developed which enable collection of endometrial tissue or luminal cells or uterine fluid. However, as these are all invasive procedures, there is a risk that sampling around the time of breeding may adversely affect subsequent pregnancy rate. This systematic review compared the pregnancy rates (PR) of cattle which underwent uterine lavage (UL), cotton swab (CS), cytobrush (CB), cytotape (CT), or endometrial biopsy (EB) sampling procedures with those that were not sampled. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol, relevant databases, including Pubmed, Web of Science, CAB Abstracts, VetMed Resource-Ruminants, and Scopus, were searched. The outcome measured was the pregnancy rate after the collection of endometrial sample(s). Seven studies, involving a total of 3693 cows, fulfilled the inclusion criteria for the systematic review and allowed the comparison of PR between sampled (n = 1254) and non-sampled cows (n = 2409). The results of the systematic review showed that endometrial sampling procedures can be performed before breeding or shortly after insemination without adversely affecting pregnancy rates in cattle. However, further studies are needed to validate this information.

Association between progesterone concentration and endometrial gene expression in dairy cows

The objective of this study was to evaluate the association between progesterone concentration on Days 4 and 9 of the estrus cycle and endometrial transcriptome at Day 9 in lactating grazing dairy cows. Blood samples were obtained on Days 0, 4, and 9 for progesterone measurement by chemiluminescence. Cows were assigned to one of the following groups (n = 3 per group): cows with low physiological progesterone on Day 4, cows in anestrous, cows with high physiological progesterone on Day 4, and superovulated cows. Endometrial biopsy samples were obtained on Day 9 for RNA sequencing. Quality control and determination of differentially expressed genes (false discovery rate <0.05) were determined using the edgeR package for R software. We identified 3,042 differentially expressed genes among the 4 groups. Cows having high physiological progesterone and superovulated cows showed high similarities and clustered apart from those in anestrus or having low physiological progesterone. Functional analysis using Database for Annotation, Visualization, and Integrated Discovery revealed that endometrial genes upregulated by low progesterone concentration are enriched genes involved in the immune system and inflammatory response. Conversely, cows with high physiological progesterone concentration presented an endometrial transcriptome with similarities to cows with good genetic merit for fertility, showing upregulation of genes related to uterine relaxation-contraction, focal adhesion, GnRH signaling pathway, and epidermal growth factor-like related terms, suggesting a favorable embryo environment. In conclusion, our results support the concept that there is a threshold of progesterone concentration at the beginning of the luteal phase associated with endometrial expression of critical genes involved in the preparation of the uterine environment for embryo implantation.

Mating to Intact, but Not Vasectomized, Males Elicits Changes in the Endometrial Transcriptome: Insights From the Bovine Model

An appropriate female reproductive environment is essential for pregnancy success. In several species, including mice, pigs and horses, seminal plasma (SP) components have been shown to modulate this environment, leading to increased embryo viability and implantation. Due to the characteristics of mating in the aforementioned species, SP comes into direct contact with the uterus. However, it is questionable whether any SP reaches the uterus in species that ejaculate inside the vagina, such as humans and cattle. Hence, we hypothesized that sperm, perhaps acting as a vehicle for SP factors, play a more important role in the modulation of the maternal uterine environment in these species. In addition, changes elicited by SP and/or sperm may originate in the vagina and propagate to more distal regions of the female reproductive tract. To test these hypotheses, a bovine model in which heifers were mated to intact or vasectomized bulls or were left unmated was used. RNA-sequencing of endometrial samples collected 24 h after mating with a vasectomized bull did not reveal any differentially expressed genes (DEGs) in comparison with control samples. However, the endometrium of heifers mated with intact bulls exhibited 24 DEGs when compared to heifers mated with vasectomized bulls, and 22 DEGs when compared to unmated control heifers. The expression of a set of cytokines (IL6, IL1A, IL8, and TNFA) and candidate genes identified in the endometrial RNA-sequencing (PLA2G10, CX3CL1, C4BPA, PRSS2, BLA-DQB, and CEBPD) were assessed by RT-qPCR in the vagina and oviductal ampulla. No differences in expression of these genes were observed between treatments in any region. However, mating to both intact and vasectomized bulls induced an increase in IL1A and TNFA expression in the vagina compared to the oviduct. These data indicate that sperm, but not secretions from the accessory glands alone, induce modest changes in endometrial gene expression after natural mating in cattle. However, it is not clear whether this effect is triggered by inherent sperm proteins or SP proteins bound to sperm surface at the time of ejaculation.

Effect of seminal plasma infusion into the vagina on the normalization of endometrial epidermal growth factor concentrations and fertility in repeat breeder dairy cows

Epidermal growth factor (EGF) concentrations in the uterus show two peaks on days 2–4 and 13–14 during the estrous cycle in fertile cows. Loss of the two peaks has been linked to reduced fertility in repeat breeder cows. This study aimed to examine the effect of seminal plasma (SP) on normalizing endometrial EGF concentrations and restoring fertility in repeat breeder cows with low EGF concentrations on day 3. In study 1, we examined the effect of the deposition sites (the vagina and uterus) of SP on the endometrial EGF concentrations in repeat breeder cows. SP infusion into the vagina, but not uterus, on the first day of the estrus cycle (day 0) normalized the endometrial EGF concentrations (≥ 4.7 ng/g tissue weight) on day 3. In study 2, the effect of SP volume (0.5 and 10 ml of SP and 0.5 ml of SP diluted to 10 ml) on EGF concentrations was examined. All groups with SP infusion had increased EGF concentrations on day 3, and cows with 10 ml of SP and 0.5 ml of SP diluted to 10 ml showed the highest levels of EGF concentrations. In study 3, we examined the effect of SP infusion on fertility. SP infusion normalized two peaks of endometrial EGF concentrations in about 60% of repeat breeder cows and produced more pregnancies than the controls (44.4 vs. 19.4%). Therefore, we concluded that SP may contain an activity to normalize the EGF profile and restore fertility in repeat breeder cows with altered EGF profiles.

Trophectoderm regeneration to support full-term development in the inner cell mass isolated from bovine blastocyst

Which comes first: tissue structure or cell differentiation? Although different cell types establish distinct structures delineating the inside and outside of an embryo, they progressively become specified by the blastocyst stage, when two types of cell lineages are formed: the inner cell mass (ICM) and the trophectoderm (TE). This inside-outside aspect can be experimentally converted by the isolation of the ICM from a blastocyst, leading to a posteriori externalization of the blastomeres composing the outermost layer of the ICM. Here, we investigated the totipotency of isolated mouse and bovine ICMs to determine whether they are competent for TE regeneration. Surprisingly, a calf was generated from the bovine isolated ICM with re-formed blastocoel (re-iICM), but no mouse re-iICMs developed to term. To further explore the cause of difference in developmental competency between the mouse and bovine re-iICMs, we investigated the SOX17 protein expression that is a representative molecular marker of primitive endoderm. The localization pattern of SOX17 was totally different between mouse and bovine embryos. Particularly, the ectopic SOX17 localization in the TE might be associated with lethality of mouse re-iICMs. Meanwhile, transcriptome sequencing revealed that some of the bovine re-iICMs showed transcriptional patterns of TE-specific genes similar to those of whole blastocysts. Our findings suggest that TE regeneration competency is maintained longer in bovine ICMs than in mouse ICMs and provide evidence that the ICM/TE cell fate decision is influenced by structural determinants, including positional information of each blastomere in mammalian embryos.

Endometrial epidermal growth factor profile and its abnormalities in dairy cows

Normal cows have 2 peaks in endometrial epidermal growth factor (EGF) concentrations on Days 2–4 and 13–14, and the absence of peaks has been linked to reduced fertility in repeat breeder (RB) cows. However, the timing of the peaks (i.e., day of examinations) was estimated for a few cows per cycle day. Therefore, the present study characterized EGF peaks and examined if the absence of peaks in RB cows indicate either peak loss or changed timing. In Study 1, 20 Holstein cows were examined for EGF concentrations between Days 1 and 6 using repeated biopsy of the uterine endometrial tissues. Sixteen cows exhibited increased EGF concentrations for 2–3 days between Days 2 and 5. All 16 cows exhibited increased EGF concentrations on Day 3. In Study 2, 10 cows were examined for EGF concentrations between Days 11 and 16. Increased EGF concentrations for 2–3 days were found in 7 cows between Days 12 and 15. All 7 cows exhibited increased EGF concentrations on Days 13 and 14. In Study 3, 12 RB cows were examined for endometrial EGF concentrations between Days 1 and 6. Four cows exhibited an increase of EGF concentrations on Days 3 and 4, whereas 8 cows (66.7%) exhibited low EGF concentrations throughout the study period. In conclusion, Days 3 and 13–14 are suitable days to examine a cyclic change of endometrial EGF concentrations. Further, low EGF concentrations on Day 3 in RB cows indicated an absence, but not altered timing, of the EGF peak.

Mitochondrial activity during pre-maturational culture in in vitro-grown bovine oocytes is related to maturational and developmental competences

The objective of this study was to investigate the dynamics of mitochondrial activity in in vitro-grown (IVG) bovine oocytes during pre-maturational culture (pre-IVM) and its relationship to their developmental competence upon being subjected to different pre-IVM durations. After 12-day IVG culture, oocytes were cultured for 0, 10 or 20 h with 3-isobutyl-1-methylxanthine (IBMX) as pre-IVM. Mitochondrial activity in IVG oocytes after 10 h pre-IVM was the highest among all the pre-IVM durations (P < 0.05). In addition, cleavage (79.4%) and blastocyst rates (38.9%) of embryos derived from IVG oocytes with 10 h pre-IVM were higher than those with 20 h pre-IVM (63.0 and 25.8%, respectively; P < 0.05) and similar to those of in vivo-grown oocytes (82.7 and 36.7%, respectively). To confirm the developmental ability of IVG oocytes with 10 h pre-IVM beyond the blastocyst stage in vivo, embryo transfer was attempted. Transferred embryos developed to the elongated embryonic stage (63.6%, 7/11) in the recipient uterus at Day 16 of oestrus, and a male calf was delivered (50%, 1/2). In conclusion, it was indicated that the mitochondrial activity of bovine IVG oocytes peaked at 10 h pre-IVM and was closely correlated with the nuclear maturation and developmental competences of IVG oocytes.

Effect of epidermal growth factor (EGF) on the phosphorylation of mitogen-activated protein kinase (MAPK) in the bovine oviduct in vitro: Alteration by heat stress

Epidermal growth factor (EGF) has been shown to be involved in control of the oviductal microenvironment. To elucidate the potential mechanisms responsible for the detrimental effect of heat stress and to identify the relation with the endocrine status, the effects of EGF on the level of phosphorylated mitogen-activated-protein kinase (MAPK) and proliferation of bovine oviductal epithelial cells (OECs) exposed to different cyclic ovarian steroidal environments (luteal phase (LP), follicular phase (FP) and postovulatory phase (PO)) and temperatures (mild heat stress (40 C) and severe heat stress (43 C)) were investigated. Western blot was performed to evaluate phosphorylated MAPK, while proliferation was analyzed by MTT assay. Stimulation of OECs with EGF alone or with EGF in the PO and FP environments significantly increased the amount of phosphorylated MAPK, with MAPK 44 phosphorylation being highest during exposure to PO conditions. These effects were not observed in the LP. Heat treatment completely blocked effects of EGF on phosphorylated MAPK. Additionally, severe heat stress led to a significantly lower basal level of phosphorylated MAPK. PD98059 (MAPK inhibitor) completely abolished EGF-stimulated MAPK phosphorylation and OECs proliferation. Overall the results indicate that EGF has the potential to increase the amount of phosphorylated MAPK in OECs and therefore could be involved in regulation of the bovine oviductal microenvironment. However, these regulatory mechanisms may be compromised in the presence of heat stress (high ambient temperature), leading to low fertility rates and impaired embryo survival.

Alteration of the endometrial EGF profile as a potential mechanism connecting the alterations in the ovarian steroid hormone profile to embryonic loss in repeat breeders and high-producing cows

Poor reproductive efficiency is a worldwide problem that has affected the dairy industry during the last several decades. In an attempt to explain the changes in reproductive physiology caused by high milk production, a model of elevated steroid metabolism in lactating dairy cows has been proposed. A slow increase in levels and low peak levels of estradiol (E₂) and progesterone (P₄) characterize endocrine changes in high producing cows. Similar changes have been reported in the repeat breeder cows. The abnormal changes in E₂ and P₄ concentrations of these cows may cause an improper uterine environment due to disturbed expression of growth factors and cytokines in the endometrium. This review focuses on the alteration in epidermal growth factor (EGF) profile in the endometrium during the estrous cycle. The normal cow has two peaks of EGF concentrations on days 2–4 and 13–14. Low concentrations of EGF on these days distinguished both high-producing and repeat breeder cows from normal cows. Alteration of the EGF profile could be found in 70 and 40% of the repeat breeder and high-producing cows, respectively. Treatment with a high dose of estradiol benzoate and an intravaginal progesterone-releasing device restored the normal EGF profile in about 70% of the affected cows. The cows having a normal EGF profile after treatment showed a higher pregnancy rate than the cows with the altered profile. Further studies to understand the etiology of the alteration in the EGF profile are needed to develop another treatment option and preventive management for this problem.

Low incidence of an altered endometrial epidermal growth factor (EGF) profile in repeat breeder Holstein heifers and differential effect of parity on the EGF profile between fertile Holstein (dairy) and Japanese Black (beef) cattle

A high incidence (about 70%) of alteration in endometrial epidermal growth factor (EGF) profile, i.e., loss of 2 peaks on days 2–4 and 13–14, has been linked to a reduced fertility in multiparous repeat breeder Holstein cows. However, the EGF profile in Holstein heifers and other breeds (types) of cattle has not been investigated. In study 1, EGF concentrations were determined using endometrial tissues obtained by biopsy on days 3, 7 and 14 from 84 fertile Holstein heifers to obtain a normal range and 53 repeat breeder Holstein heifers to estimate incidence of alterations in the EGF profile. In repeat breeder heifers, EGF concentrations were similar to fertile controls on 3 days and five animals (9.4%) had an altered EGF profile with EGF concentrations below the normal range on days 3 and 14. In study 2, EGF concentrations on day 3 were repeatedly examined from the nulliparous period to the third postpartum period in 28 Holstein (dairy) and 47 Japanese Black (beef) cattle. The effect of parity on EGF concentrations on day 3 was different between Holstein and Japanese Black cattle. In Japanese Black cows, the EGF concentrations were consistently high throughout the study period, while in Holstein cows, the EGF concentrations decreased after the second calving. In conclusion, unlike multiparous repeat breeder Holstein cows, an altered EGF profile may not be a major cause of repeat breeding in Holstein heifers, and the peak EGF concentrations around day 3 may decrease even in fertile populations of multiparous dairy cows, but not in beef cows.

EGF and TGF-alpha supplementation enhances development of cloned mouse embryos

In this study, we sought to determine the extent to which mitogenic growth factors affect the survival and development of cloned mouse embryos in vitro. Cloned embryos derived by intracytoplasmic nuclear injection (ICNI) of cumulus cell nuclei into enucleated oocytes were incubated in culture media supplemented with EGF and/or TGF-alpha for 4 days. Compared to control, treatment with either growth factor significantly increased the blastocyst formation rate, the total number of cells per blastocyst, the cell ratio of the inner cell mass and the trophectoderm (ICM:TE ratio), and EGF-R protein expression in cloned embryos. In most instances these effects were enhanced in cloned embryos when EGF and TGF-alpha were combined. Although fewer blastocysts developed from cloned than from fertilized one-cell stage embryos, growth factor treatment appeared to have the greatest effect on cloned embryos. These results demonstrate that mitogenic growth factors significantly enhance survival and promote the preimplantation development of cloned mouse embryos.