Relationships between maternal hormone secretion and embryo development on day 5 of pregnancy in dairy cows

The role of the oviduct environment in embryo survival

CONTEXT

Declining fertility is an issue in multiple mammalian species. As the site of fertilisation and early embryo development, the oviduct plays a critical role in embryo survival, yet there is a paucity of information on how the oviduct regulates this process.

AIMS

We hypothesised that differences in steroid hormone signalling and/or immune function would be observed in a model of poor embryo survival, the peripubertal ewe.

METHODS

We examined expression of steroid hormones in systemic circulation, oviductal expression of oestrogen receptorαand genes important in steroid hormone signalling, and immune function in pregnant and cyclic peripubertal and adult ewes on day 3 after oestrus.

KEY RESULTS

Concentrations of progesterone, but not oestradiol, were decreased in the peripubertal ewe compared to the adult ewe. Oestrogen receptorαprotein expression was increased in the peripubertal ewe, but pathway analysis of gene expression revealed downregulation of the oestrogen signalling pathway compared to the adult ewe. Differential expression of several genes involved in immune function between the peripubertal and adult ewe was consistent with an unfavourable oviductal environment in the peripubertal ewe lamb. Oestradiol concentration was positively correlated with the expression of multiple genes involved in the regulation of immune function.

CONCLUSIONS

Differences in the immune environment of the oviduct, potentially linked to differential modulation by steroid hormones, may partially underly the poor fertilisation and early embryo survival observed in the peripubertal ewe.

IMPLICATIONS

A unfavourable oviductal environment may play an important role in limiting reproductive success.

Mastitis impact on high-yielding dairy farm's reproduction and net present value

Poor udder health can have a negative impact on milk production and reproductive performance, which reduces the net present value (NPV) of dairy farms. The aim of this study is therefore to investigate the relationship between clinical mastitis and NPV and the financial impact of impaired reproductive function. For this purpose, 473 dairy cows were included in our study, 146 cows with clinical mastitis (CM group) and 327 clinically healthy cows (CH group) from a high-yielding dairy farm in Romania, milking approximately 780 dairy cows with an average milk production of 46 kg milk/day. We found that, in contrast to CH cows, CM cows had a significantly lower conception rate at first service (58.2% vs. 41.7%, p < 0.05), third service (45.3% vs. 30.2%, p < 0.05), and total services (49.2% vs. 36.4%, p < 0.05). However, this positive effect was not observed for the average days open, which were significantly lower in CM cows than in CH cows (112 ± 4.3 days vs. 142 ± 3.1 days, p < 0.05). The fact that the non-pregnant CH cows had higher somatic cell counts (>400,000 SCC/mL) in their milk around artificial insemination (AI) and 1 month earlier than the pregnant cows (<250,000 SCC/ml) supports the idea that poor uterine health affects the reproductive activity of high-yielding cows. However, by using the UW-DairyRepro$ decision support tool, we found that despite the impairment of reproductive function in dairy cows, the largest negative impacts on NPV are still the cost of milk loss (US$14,439.4/farm/year) and treatment costs (US$4,380/farm/year). We considered the costs associated with poor reproductive function in the CM group (US$3,577/farm/year) as an additional cost of mastitis. Finally, it appears that the impact of mastitis on reproduction is associated with a lower chance of conception than it is with a daily risk of services.

Post-mating Diclofenac vs. Carprofen treatment on serum progesterone levels and reproductive outcomes in Hungarian-Merino ewes during the non-breeding season

The maternal recognition process is crucial for establishment of healthy pregnancy. In this process, anti-luteolitic applications are one of the main reproductive strategies to manage the embryonic losses and maximize reproductive profitability in farm animals. The aim of this study was to investigate the efficacy of post-mating NSAID treatments on reproductive parameters (pregnancy rate, lambing rate, multiple birth rate, litter size) and serum progesterone levels in ewes stimulated with progesterone outside of the breeding season. For this purpose, two different experiments (diclofenac and carprofen) were conducted in the same ewe flock induced with short-term progestagen based protocol in the non-breeding season of two consecutive years. In experiment 1 (n=85), 42 ewes were injected with 2.5 mg/kg Diclofenac on the 9th and 10th days post-mating and the rest were not treated and served as control. In experiment 2 (n=82), 40 ewes were injected with 1.4 mg/kg Carprofen on the 9th days post-mating and the rest were not treated as control. In both experiments, blood samples were collected from all ewes on days 9, 12 and 13 post-mating to measure serum progesterone levels. In both experiments, there were no differences both reproductive parameters and serum progesterone levels when compared to the control groups. It was concluded that post-mating diclofenac and carprofen treatments in the critical period have no significant effects on both reproductive parameters and serum progesterone levels in ewes in the non-breeding season.

The Occurrence of a Negative Energy Balance in Holstein-Friesian and Simmental Cows and Its Association with the Time of Resumption of Reproductive Activity

Intensive lactation (lactogenesis) in cows is conducive to a negative energy balance (NEB), so the search for traits associated with the physiological capacity to cope with its consequences is a current area of research. This is especially important because NEB overlaps with the resumption of the reproductive cycle, which determines the profitability of herds. This study analysed the relationship between NEB and the time of resumption of reproductive activity in cows with varying genetic potential (Simmental and Holstein-Friesian), fed a similar diet (TMR). The aim of the study was to analyse the dependencies between NEB markers and changes in progesterone levels between 25 and 31 days postpartum. A strong positive correlation was shown between daily milk production (DMP) and loss of body condition (LBCS; 0.772; p ≤ 0.05). These parameters were associated with the levels of NEB biomarkers. Higher values of NEB indicators (LBCS, C16:0, C18:1, NEFA, and BHBA) were usually noted during periods with higher DMP (II and III). The trends observed were confirmed by positive correlation coefficients (r), which ranged from 0.324 to 0.810 (p ≤ 0.05). The reverse trend was noted for glucose and leptin, which decreased as productivity increased, as confirmed by r values from -0.368 to -0.530 (p ≤ 0.05). In both breeds, the glucose and leptin levels decreased as DMP increased. Higher values for NEB indicators were shown to be negatively correlated with progesterone levels (r from -0.300 to -0.712; p ≤ 0.05), and a lower progesterone level was associated with a longer calving-to-first-service interval and calving-to-conception interval. The rate of postpartum triglyceride release depends on daily milk production, and therefore the adaptability of the liver should be considered an important element of mitigation of the consequences of NEB. This may have practical applications by extending productive life, which is often shortened due to deteriorating reproductive performance.

Effect of flunixin meglumine and aspirin administration on conception rate and estrous cycle characteristics of Egyptian Baladi cows during hot season

The current investigation aims to evaluate the effects of flunixin meglumine (FM) and aspirin as non-steroid anti-inflammatory drug (NSAID) administration on estrous cycles characteristics and conception rate of Egyptian Baladi cows during hot season. In the first phase, 30 cows were divided into 3 groups, 10 cows for each treatment. The first group was treated with FM at the rate of 1.1 mg/kg body weight (BW) intramuscular, while the second group was administrated aspirin solution orally at the rate of 50 mg/kg BW. The third group was assigned as control (CG) that has no treatment. The FM group was administrated on day 14 after mating, while aspirin was given on day 14 and day 15 post-mating. All cows were mated naturally after showing estrus signs. Pregnancy diagnosis was carried 60 days after mating by rectal palpation. In the second phase, cows were monitored for estrus behavior by visual observation twice a day. The length of normal estrous cycles was 20, 23, and 22 days in cows treated with FM, aspirin, and control cows, respectively. There was no significant effect of treatment on the length of normal estrous cycles in Egyptian cows (P < 0.05). Proportions of long cycles in Egyptian cows that treated with FM or aspirin and control were 75, 67.7, and 57.1%, respectively. Short cycles were completely absent in cows that treated with FM or aspirin, but it was 29% in CG. Mounting behavior and tail rising were not detected in CG compared to 0 and 33% in FM or 25 and 33% in aspirin treated cows, respectively. Conception or pregnancy rate were 60, 40, and 30%, respectively, in FM, aspirin treated, and CG. Treatment cows whether FM or aspirin group did not influence (P < 0.05) progesterone concentration during the 14 days and 21 days from estrous cycle in pregnant and non-pregnant Egyptian Baladi cows than CG. In conclusion, the results of this study clearly indicated beneficial effect of FM and aspirin administration on intense of displayed estrous behavior and conception rate of Egyptian Baladi cows during the hot season.

Use of on-farm milk progesterone information to predict fertility outcomes in dairy cows subjected to timed artificial insemination

The objectives of this study were to evaluate the use of a qualitative on-farm milk progesterone test to predict non-pregnancy in dairy cows. Lactating Jersey cows (n = 752) were subjected to the 5-d Cosynch-72 protocol for timed artificial insemination (AI; d -8 GnRH, d -3 and -2 PGF_2α, d 0 GnRH and timed AI). Milk was sampled on d -3, 0, 7, and 28 relative to timed AI, and progesterone concentrations were assessed using a lateral flow immunochromatographic test. Samples were classified into 3 groups indicative of high (hP4; test line not visible or lighter than reference), intermediate (iP4; test line similar to reference), and low (lP4; test line darker than reference) progesterone concentrations. Blood was sampled from a subset of cows (n = 50) on d -3, 0, 7, and 28 relative to timed AI, and plasma progesterone concentrations were determined by RIA. Cows were observed daily for signs of estrus based on removal of tail paint. Pregnancy was diagnosed by ultrasonography on d 34 and 62 after AI. Plasma progesterone concentrations across all time points were greater for hP4 (3.13 ± 0.20 ng/mL) followed by iP4 (1.12 ± 0.27 ng/mL) and lP4 (0.38 ± 0.23 ng/mL). Cows in lP4 on d -3 had lesser pregnancy per AI (P/AI) compared with iP4 and hP4 (17.4, 38.3, and 37.2%, respectively). For measurements performed on the day of AI (d 0), lP4 cows had greater P/AI compared with hP4 and iP4 (34.8, 0.0, and 15.6%, respectively), and the risk of pregnancy loss tended to be greater for iP4 compared with lP4. Cows in lP4 on d 7 after AI had lesser P/AI than those in iP4 and hP4 (12.0, 34.0, and 37.7%, respectively). Cows classified as lP4 on d 28 had the least P/AI on d 62 followed by iP4 and then hP4 (0.8, 9.2, and 59.4%, respectively) and were at the greatest risk for pregnancy loss (lP4 = 74.6%, iP4 = 8.4%, hP4 = 7.1%). Sensitivity and specificity to predict non-pregnancy on d 62 were 0.86 and 0.32 (d -3), 0.95 and 0.15 (d 0), 0.93 and 0.23 (d 7), and 0.99 and 0.53 (d 28), respectively. On-farm milk progesterone profiling using a lateral flow immunochromatographic test was able to identify cows without functional corpus luteum and to predict fertility outcomes following timed AI.

Biomarkers of fitness and welfare in dairy cattle: healthy productivity

Milk production intensification has led to several unwanted aspects, such as sustainability issues and environmental pollution. Among these, increased milk outputs that have been achieved over the last 70 years have led to several health and pathophysiological conditions in high yielding dairy animals, including metabolic diseases that were uncommon in the past. Increased occurrence of diverse metabolic diseases in cattle and other domestic animals is a key feature of domestication that not only affects the animals' health and productivity, but also may have important and adverse health impacts on human consumers through the elevated use of drugs and antibiotics. These aspects will influence economical and ethical aspects in the near future. Therefore, finding and establishing proper biomarkers for early detection of metabolic diseases is of great interest. In the present review, recent work on the discovery of fitness, stress and welfare biomarkers in dairy cows is presented, focusing in particular on possible biomarkers of energy balance and oxidative stress in plasma and milk, and biomarkers of production-related diseases and decreased fertility.

Transcriptome profile and association study revealed STAT3 gene as a potential quality marker of bovine gametes

The present study was aimed to investigate differences in molecular signatures in oocytes derived from Holstein-Friesian heifers with different genetic merit for fertility, euthanized during day 0 or day 12 of the estrous cycle. Moreover, association between single nucleotide polymorphisms (SNPs) of ODC1 and STAT3 genes and bull fertility traits was investigated. The gene expression patterns were analyzed using cDNA array and validated with quantitative real-time polymerase chain reaction (PCR). The result revealed that several genes have shown not only to be regulated by fertility merit but also by the day of oocyte recovery during the estrous cycle. The STAT3 gene was found to be upregulated in oocytes recovered from animals with high fertility merit at both day 0 and day 12. Some other genes like PTTG1, ODC1 and TUBA1C were downregulated at day 0 and upregulated at day 12 in high, compared with low, fertility merit recovered oocytes. In contrast, the transcript abundance of TPM3 was upregulated at day 0 and downregulated at day 12 in high, compared with low, fertility merit recovered oocytes. In addition, ODC1 and STAT3 were found to be associated (P < 0.05) with sperm quality traits as well as flow cytometry parameters. Therefore, the expression of several candidate genes including ODC1 and STAT3 was related to the genetic merit of the cow. In addition polymorphisms in these two genes were found to be associated with bull semen quality.

Parenteral Zinc Supplementation Increases Pregnancy Rates in Beef Cows

Zinc (Zn) is required for normal reproductive performance in cattle. The aim of this study was to evaluate the effect of subcutaneous injection of 400 mg Zn at the beginning of fixed-time artificial insemination (FTAI) on preovulatory follicle and corpus luteum (CL) size, plasma estradiol (E2) and progesterone (P4) concentrations, and pregnancy rates in beef cows. Copper (Cu) concentration and alkaline phosphatase (ALP) activity in plasma were also evaluated. Zinc supplementation at the beginning of the FTAI protocol (day 0) increased the area of preovulatory follicle (APF, day 9; P = 0.042) and plasma P4 concentration (day 16; P = 0.01), whereas plasma E2 concentration (day 9) and area of CL (ACL; day 16) were not modified by Zn supplementation in cows with adequate plasma Zn concentration. Zinc supplementation in Zn-deficient cows increased ACL with respect to controls (P = 0.048) but did not modify plasma E2 concentration. Pregnancy rate on day 41 after FTAI was higher in cows supplemented with Zn compared with controls (80.95% and 51.61%, respectively; P = 0.042). Plasma Zn and Cu concentrations on days 7, 9, and 16 were not affected by Zn supplementation. In conclusion, the results obtained in the present study determined that parenteral Zn supplementation at the beginning of the FTAI protocol increased preovulatory follicle size, plasma P4 concentration, and pregnancy rates in beef cows.

Effect of chronic administration of a gonadotropin-releasing agonist on luteal function and pregnancy rates in dairy cattle

Increased embryonic losses may be associated with inadequate progesterone (P4) concentrations in high-producing lactating dairy cattle. The objectives of the present studies were to determine if chronic administration of a gonadotropin-releasing hormone (GnRH) agonist, Deslorelin, would increase circulating P4 concentrations and subsequently increase pregnancy rates in dairy cattle. Administration of Deslorelin for 12 days increased (p < .05) luteal volume and circulating P4 concentrations in primiparous lactating dairy cows, but increased only luteal volumes in multiparous cows. Treatment with Deslorelin increased Day 45 pregnancy rates in cows as compared to untreated controls. Chronic treatment with Deslorelin in dairy cattle; (a) increased luteal volume of the primary CL, (b) induced accessory CL, (c) increased circulating P4 concentration in primiparous cows only, (d) did not lengthen the estrous cycle upon removal of treatment, and (e) increased pregnancy rates. Although luteal volume was increased in multiparous cows and circulating P4 concentrations were not with Deslorelin treatment, there was an apparent effect on pregnancy rates. This hormonal strategy may represent a suitable model to address local effects of P4 and GnRH/luteinizing hormone on uterine environment and subsequent embryonic survival.

Expression of oestrogen receptor, androgen receptor and progesterone nuclear receptor in sheep uterus during the oestrous cycle

Oestrogen, androgen and progesterone are involved in the regulation of uterine physiological functions, with the participation of the following proteins: oestrogen receptor (ER), androgen receptor (AR) and progesterone nuclear receptor (PGR). In this study, we used immunohistochemistry to detect the localization of ERα, ERβ, AR and PGR in sheep uterus. Additionally, we used real-time polymerase chain reaction (RT-qPCR) and Western blot technique to analyse their expression profiles at different stages of sheep oestrous cycle in the endometrium and myometrium. Immunohistochemical analysis showed that ERα, ERβ, AR and PGR were present in sheep uterus in oestrus, mainly in the uterine luminal epithelium, stroma, gland and myometrium. Real-time polymerase chain reaction results showed that in the endometrium, ERα expression level was highest in oestrus. ERβ and PGR, instead, were highly expressed in pro-oestrus. In the myometrium, ERα was highly expressed in both oestrus and pro-oestrus, and ERβ was highly expressed in oestrus and dioestrus. Progesterone nuclear receptor expression was highest in oestrus, followed by metoestrus. In the endometrium, both receptors ERα and ERβ were abundant in pro-oestrus, while the maximum AR protein content was found in oestrus. At this stage of the oestrous cycle, PGR protein concentration in the myometrium was significantly lower than those observed in other stages. These results suggest that these receptors are important for sheep reproductive function, as their expression at mRNA and protein levels exhibits particular time- and tissue-specific profiles along the oestrous cycle.

Intraoviductal concentrations of steroid hormones during in vitro culture changed phospholipid profiles and cryotolerance of bovine embryos

The objective of this study was to evaluate the effect of progesterone (P4), estradiol (E2), and cortisol (CO) at intraoviductal concentrations on bovine embryo development and quality in vitro. After fertilization of in vitro matured oocytes, zygotes were cultured for 8 days in synthetic oviductal fluid, supplemented with 55 ng/ml P4, 120 pg/ml E2, 40 ng/ml CO, or their combination (ALL). Control embryos were cultured with vehicle (0.1% ethanol). Exposure to steroids did not affect the embryo developmental rate nor the mean number of cells per blastocyst. However, at 24 hr after vitrification-warming, exposure to P4 improved the proportion of embryos that re-expanded and were viable while exposure to CO decreased the proportion of viable embryos. By intact cell MALDI-TOF mass spectrometry, a total of 242 phospholipid masses of 400-1000 m/z were detected from individual fresh blastocysts. Exposure to ALL induced the highest and most specific changes in embryo phospholipids, followed by P4, E2, and CO. In particular, the m/z 546.3 and 546.4 attributed to lysophosphatidylcholines were found less abundant after exposure to P4. In conclusion, exposure of bovine embryos to intraoviductal concentrations of steroid hormones did not affect in vitro development but changed blastocyst quality in terms of cryotolerance and phospholipid profiles.

Genetic merit for fertility traits in Holstein cows: VI. Oocyte developmental competence and embryo development

The hypothesis of this study was that cows with good genetic merit for fertility traits (Fert+) would produce oocytes and embryos of greater quality than cows with poor genetic merit for fertility traits (Fert-) and that mRNA expression of candidate genes would reflect the observed differences in quality. The aim of the study, therefore, was to determine the effect of genetic merit for fertility traits on morphological classification and mRNA abundance of key genes in immature oocytes and cumulus cells following ovum pick-up and in embryos following superovulation, artificial insemination (AI), and uterine flushing. In experiment 1, 17 Fert+ and 11 Fert- cows, ranging from 54 to 84 d in milk, were submitted to ovum pick-up on 4 occasions during a 2-wk period. Recovered cumulus-oocyte complexes (COC) were morphologically graded. Oocytes and cumulus cells were separated, and mRNA abundance of genes associated with oocyte developmental competence was measured. There was no effect of genotype on the distribution of COC grades or on the mRNA abundance of the candidate genes in grade 1 COC. In experiment 2, 20 Fert+ and 19 Fert- cows, ranging from 71 to 189 d in milk, were submitted to superovulation and AI. The uteri of cows that responded to the superovulation protocol (17 Fert+ and 16 Fert- cows) were nonsurgically flushed 7 d postovulation. Recovered embryos were morphologically graded, and mRNA abundance of genes associated with embryo development was measured in grade 1 blastocysts. The response to the superovulation protocol was assessed by counting the number of codominant follicles on the day of AI, which was similar for both genotypes (22.0 ± 9.7 and 19.8 ± 8.2 for Fert+ and Fert- cows, respectively). There was no effect of genotype on the proportion of transferable embryos recovered or on the mRNA abundance of the candidate genes tested in the grade 1 blastocysts. Of the total embryos classified as blastocysts, however, the Fert+ cows tended to have a greater proportion of grade 1 blastocysts compared with Fert- cows (90% vs. 64%, respectively). In conclusion, genetic merit for fertility traits had a no effect on mRNA abundance of the candidate genes that were examined in immature oocytes and cumulus cells and in embryos recovered after superovulation. The observed differences in morphological blastocyst quality following superovulation would suggest that the superior reproductive performance of Fert+ cows could arise during the later stages of embryo development from d 7 until maternal recognition of pregnancy.

Effect of plasma progesterone on oocyte recovery, oocyte quality, and early in-vitro developmental competence of embryos in Bos indicus dairy cows

The objective of present study was to determine the effect of plasma progesterone (P4) on oocyte recovery, oocyte quality, and early in-vitro developmental competence of embryos in Bos indicus dairy cows. The ovaries were collected in an abattoir. These ovaries (n = 750) were divided into two groups: 1) estrous CYCLIC (n = 318), and 2) estrous ACYCLIC (n = 432). Mean serum concentrations of P4 in a subset of (n = 85; 4.21 ± 0.4 ng/ml compared with 0.5 ± 0.2 ng/ml; P <  0.05) were greater in estrous CYCLIC as compared to ACYCLIC cows, respectively. The mean number of oocytes recovered per ovary (6.5 ± 0.5 compared with 4.0 ± 0.2; P <  0.05) was greater for estrous CYCLIC than ACYCLIC cows, respectively. The oocytes with grade I_+_II quality (55.3% compared with 47.6%; P <  0.05) were greater, whereas, there was lesser percentage with grade III_+_IV quality (44.5% compared with 52.4%; P <  0.05) from estrous CYCLIC as compared with ACYCLIC cows, respectively. Cleavage rate (70.9% compared with 52.8%; P < 0.05) was greater for embryos derived from estrous CYCLIC than ACYCLIC cows, respectively. Similarly, the embryo developmental rates to the 8- (38.5% compared with 20.8%; P < 0.05) and 16- (20.0% compared with 10.9%; P < 0.05) cell stage were greater for embryos derived from estrous CYCLIC as compared to ACYCLIC cows, respectively. In conclusion, the presence of greater plasma P4 has a beneficial effect on oocyte recovery, oocyte quality, and early IVEP outcomes in Bos indicus dairy cows.

Effects of nutrition and genetics on fertility in dairy cows

Optimal reproductive function in dairy cattle is mandatory to maximise profits. Dairy production has progressively improved milk yields, but, until recently, the trend in reproductive performance has been the opposite. Nutrition, genetics, and epigenetics are important aspects affecting the reproductive performance of dairy cows. In terms of nutrition, the field has commonly fed high-energy diets to dairy cows during the 3 weeks before calving in an attempt to minimise postpartum metabolic upsets. However, in the recent years it has become clear that feeding high-energy diets during the dry period, especially as calving approaches, may be detrimental to cow health, or at least unnecessary because cows, at that time, have low energy requirements and sufficient intake capacity. After calving, dairy cows commonly experience a period of negative energy balance (NEB) characterised by low blood glucose and high non-esterified fatty acid (NEFA) concentrations. This has both direct and indirect effects on oocyte quality and survival. When oocytes are forced to depend highly on the use of energy resources derived from body reserves, mainly NEFA, their development is compromised due to a modification in mitochondrial β-oxidation. Furthermore, the indirect effect of NEB on reproduction is mediated by a hormonal (both metabolic and reproductive) environment. Some authors have attempted to overcome the NEB by providing the oocyte with external sources of energy via dietary fat. Conversely, fertility is affected by a large number of genes, each with small individual effects, and thus it is unlikely that the decline in reproductive function has been directly caused by genetic selection for milk yield per se. It is more likely that the decline is the consequence of a combination of homeorhetic mechanisms (giving priority to milk over other functions) and increased metabolic pressure (due to a shortage of nutrients) with increasing milk yields. Nevertheless, genetics is an important component of reproductive efficiency, and the incorporation of genomic information is allowing the detection of genetic defects, degree of inbreeding and specific single nucleotide polymorphisms directly associated with reproduction, providing pivotal information for genetic selection programs. Furthermore, focusing on improving bull fertility in gene selection programs may represent an interesting opportunity. Conversely, the reproductive function of a given cow depends on the interaction between her genetic background and her environment, which ultimately modulates gene expression. Among the mechanisms modulating gene expression, microRNAs (miRNAs) and epigenetics seem to be most relevant. Several miRNAs have been described to play active roles in both ovarian and testicular function, and epigenetic effects have been described as a consequence of the nutrient supply and hormonal signals to which the offspring was exposed at specific stages during development. For example, there are differences in the epigenome of cows born to heifers and those born to cows, and this epigenome seems to be sensitive to the availability of methyl donor compounds of the dam. Lastly, recent studies in other species have shown the relevance of paternal epigenetic marks, but this aspect has been, until now, largely overlooked in dairy cattle.

Extent and pattern of pregnancy losses and progesterone levels during gestation in Swedish Red and Swedish Holstein dairy cows

Background

Pregnancy loss is a major source of infertility in dairy cows. Despite a fertilization rate after insemination (AI) of approximately 90%, calving rates are 30%–50%, indicating the occurrence of extensive embryonic and foetal losses. The aim of this study was to establish the extent and pattern of embryonic and foetal loss in Swedish Red (SR) and Swedish Holstein (SH) dairy cows, as well as, the relationship to oestrus intensity (OI) and progesterone (P4) concentration. In total, 2130 AIs and 16,176 milk P4 samples from 359 SR and 212 SH dairy cows were included in the study. Pregnancy losses were estimated using data from P4 values combined with AI information and calving data.

Results

Total pregnancy loss from AI to the day of calving was 65%. Early embryonic loss, late embryonic loss and foetal loss were estimated to be 29, 14 and 13%, respectively. There is strong evidence in the literature that P4 concentrations at different time points are associated with pregnancy loss. In the present study, cows with pregnancy losses had significantly higher P4 levels at the day of AI and significantly lower P4 concentration at days 10, 21 and 30 after AI compared to pregnant cows. Swedish Red cows had significantly lower total pregnancy losses compared to SH cows (62% and 68% respectively, P = 0.017). Early embryonic loss was 6.7% points lower for cows inseminated at a stronger OI (OI = 3) compared to at a weaker OI (OI = 2, P = 0.006). Cows inseminated at ovulation number ≥ 5 had significantly lower early pregnancy losses compared to cows inseminated at first or second ovulation (11.5 and 8% points, respectively, P < 0.05). With an increase of one SD of milk (448 kg ECM) during the first 60 days in milk, early embryonic loss increased by 4.7% points (P = 0.006).

Conclusions

It is important to increase the number of cows calving per insemination by reducing embryo/foetal loss. This outcome can be achieved by management and breeding for optimal P4 levels at critical time points, and by considering oestrus expression in the breeding programmes to facilitate the correct timing of insemination.

The effects of nutrient restriction on mRNA expression of endogenous retroviruses, interferon-tau, and pregnancy-specific protein-B during the establishment of pregnancy in beef heifers

We hypothesize that syncytin-Rum1, bovine endogenous retrovirus-K1 (BERV-K1), pregnancy-specific protein-B (PSP-B), and interferon-τ (IFN-τ) will be influenced by maternal nutrient restriction and be differentially expressed during key stages (day 16, 34, and 50) of the establishment of gestation when fed to meet industry standards. Commercial crossbred heifers (n = 49) were maintained on a total mixed ration and supplemented with dried distillers grains with solubles. All heifers were subjected to 5-d CO-Synch + CIDR estrus synchronization protocol. Non-pregnant, non-bred control (NP-NB) heifers (n = 6) were ovariohysterectomized on day 16, and the remaining heifers were AI to a single Angus sire (day of breeding = day 0). On the day of breeding, heifers were randomly assigned to dietary treatments. One half were assigned to control treatment (CON) targeted to gain 0.45 kg/d, and the remaining half were assigned to restricted treatment (RES), which received 60% of control diets. Heifers were subjected to ovariohysterectomy on day 16, 34, or 50 of gestation. Utero-placental tissues were obtained from the uterine horn ipsilateral (P) and contralateral (NP) to the corpus luteum and separated into maternal caruncle (CAR), maternal endometrium, inter-caruncle, (ICAR), and fetal membrane (FM). There were no interactions between stage of gestation and nutritional treatment for syncytin-Rum1 or PSP-B (P > 0.22). Expression of BERV-K1 was influenced by a treatment × stage of gestation interaction (P = 0.03) in NP-CAR. On day 50, heifers fed the CON diet had greater BERV-K1 expression compared with CON heifers on day 16 and 34 and RES heifers at all sampling time points. There was a treatment × stage of gestation interaction (P < 0.01) for IFN-τ in FM tissue. On 16 d, mRNA expression of IFN-τ was greater (P < 0.01) compared with day 34 and 50 for both CON and RES heifers, but RES FM had greater (P < 0.01) IFN-τ expression compared with CON FM. In P-CAR, PSP-B expression increased (P < 0.01) by 18 000-fold on day 50 compared with NP-NB heifers. In P-ICAR, expression of syncytin-Rum1 in P-ICAR was greater (P = 0.01) on day 16 with a 14.14-fold increase compared with relative expression on day 34 and 50; whereas, PSP-B was increased (P < 0.01) on day 34 and 50 compared with day 16. In conclusion, 40% nutrient restriction had limited influence on mRNA of ERVs, PSP-B, and IFN-τ but stage of gestation differences reinforced the importance of these genes during the establishment of pregnancy.

Endogenous retroviral gene elements (syncytin-Rum1 and BERV-K1), interferon-τ, and pregnancy associated glycoprotein-1 are differentially expressed in maternal and fetal tissues during the first 50 days of gestation in beef heifers

We hypothesized that the endogenous retroviruses [ERV: syncytin-Rum1 and (BERV-K1)], and pregnancy hormones [interferon-τ (IFN-τ), and pregnancy associated glycoprotein-1 (PAG-1)] would be differentially expressed whereas progesterone and insulin concentrations in maternal blood would remain steady during early gestation. To test this hypothesis Angus crossbred heifers (n = 46; ∼15 mo of age; BW = 363 ± 35 kg) were fed native grass hay, supplemented with cracked corn to gain 0.3 kg/d, and given ad libitum access to water. All heifers were subjected to a 5-d CO-Synch + CIDR estrous synchronization protocol and AI (breeding = d 0). Ovariohysterectomies were performed on d 16, 22, 28, 34, 40, and 50 of gestation and at d 16 of the estrous cycle for non-pregnant (NP) controls. Utero-placental tissues [maternal caruncle (CAR); maternal intercaruncular endometrium (ICAR); and fetal membranes, (FM, chorion on d 16, chorioallantois on d 22 to 50)] were collected from the uterine horn ipsilateral to the corpus luteum (CL). Tissues were flash frozen and stored at –80°C. Expression of mRNA was evaluated using qPCR. In CAR, syncytin-Rum1 expression was greater (P < 0.01) on d 50 (81.5-fold) compared with NP controls or any other day of early pregnancy. In contrast, syncytin-Rum1 expression in I-CAR only tended (P = 0.09) to change across days of early pregnancy and did not differ (P = 0.27) in FM tissues. In CAR, the expression of BERV-K1 was not different (P > 0.79) at d 16 and 22, was intermediate at d 28, 34, and 40, and was greatest on d 50 (108-fold increase compared with NP). Expression of BERV-K1 in FM was increased (P < 0.01) on d 28, 34, and 50 compared with NP controls, but at d 40 did not differ from NP controls. The mRNA expression of IFN-τ in FM at d 22 was greater (P < 0.01) than all other days of gestation. In CAR, expression of PAG-1 increased (P < 0.001) dramatically on d 40 (20,000-fold) and d 50 (86,000-fold) compared with NP heifers (P < 0.01). In ICAR, expression of PAG-1 was greater (P < 0.05) on d 28 and 40 (fold increases of 113 and 102, respectively, compared with NP). Insulin concentrations were not different (P = 0.53) but progesterone was greater (P < 0.01) on d 16, 22, 28, 34, and 40 compared with d 50 of gestation. These data confirm differential ERV, IFN-τ, and PAG-1 gene expression during critical time points of early gestation in utero-placental tissues.

Weight gain potential affects pregnancy rates in bovine embryo recipients raised under pasture conditions

The aim of the present study was to evaluate the effect of differences in body weight gain after embryo transfer on the pregnancy rates of crossbred heifers used as recipients and raised under a grazing system. The study was performed during the dry (April to September) and the rainy (October to March) seasons. The embryos transferred were produced by in vitro fertilization. The body weight of each recipient was measured immediately before the embryo transfer and 23 to 25 days later, when the diagnosis of pregnancy was performed by ultrasonography. The associations among initial body weight (IBW), daily body weight gain (DWG), season, and pregnancy rate were evaluated using a logistic procedure that included the effect of the IBW, season, and linear and quadratic effects of the DWG. Altogether, there was no effect of season and pregnancy rates did not change between the dry and rainy seasons (42.3 vs. 45.8%, respectively; P > 0.05). However, the pregnancy rate was greater in the recipients with daily body weight gains over 250 g/day, regardless of the season. In addition, the pregnancy rate of the recipients was better (P < 0.04) explained by a logistic regression model that included the linear and quadratic effects of the DWG. The probability of each heifer to become pregnant according to DWG is explained by the follow equation: P(y = 1) = (Exp((-1.06703 + 0.0108 * DWG - 0.00002 * DWG ^ 2)))/(1 + Exp((-1.6703 + 0.0108 * DWG - 0.00002 * DWG ^ 2))). In conclusion, body weight gain potential is a critical factor for the pregnancy rates of in vitro embryo recipients managed under grazing systems.

Triennial Reproduction Symposium: deficiencies in the uterine environment and failure to support embryonic development

Pregnancy failure in livestock can result from failure to fertilize the oocyte or embryonic loss during gestation. The focus of this review is on cattle and factors affecting and mechanisms related to uterine insufficiency for pregnancy. A variety of factors contribute to embryonic loss and it may be exacerbated in certain animals, such as high-producing lactating dairy cows, and in some cattle in which estrous synchronization and timed AI was performed, due to reduced concentrations of reproductive steroids. Recent research in beef cattle induced to ovulate immature follicles and in lactating dairy cows indicates that deficient uterine function is a major factor responsible for infertility in these animals. Failure to provide adequate concentrations of estradiol before ovulation results in prolonged effects on expression and localization of uterine genes and proteins that participate in regulating uterine functions during early gestation. Furthermore, progesterone concentrations during early gestation affect embryonic growth, interferon-tau production, and uterine function. Therefore, an inadequate uterine environment induced by insufficient steroid concentrations before and after ovulation could cause early embryonic death either by failing to provide an adequate uterine environment for recognition of embryo signaling, adhesion, and implantation or by failing to support appropriate embryonic growth, which could lead to decreased conceptus size and failed maternal recognition of pregnancy.

Genetic control of reproduction in dairy cows

The advent of AI has markedly improved the production potential of dairy cows in all systems of production and transformed the dairy industry in many countries. Unfortunately, for many years breeding objectives focused solely on milk production. This resulted in a major decline in genetic merit for fertility traits. In recent years, the underlying physiological mechanisms responsible for this decline have started to be unravelled. It is apparent that poor genetic merit for fertility traits is associated with multiple defects across a range of organs and tissues that are antagonistic to achieving satisfactory fertility performance. The principal defects include excessive mobilisation of body condition score, unfavourable metabolic status, delayed resumption of cyclicity, increased incidence of endometritis, dysfunctional oestrus expression and inadequate luteal phase progesterone concentrations. On a positive note, it is possible to identify sires that combine good milk production traits with good fertility traits. Sire genetic merit for daughter fertility traits is improving rapidly in the dairy breeds, including the Holstein. With advances in animal breeding, especially genomic technologies, to identify superior sires, genetic merit for fertility traits can be improved much more quickly than they initially declined.

Effect of progesterone on embryo survival

Increased genetic selection over the past 40 years has resulted in a dairy cow with an improved biological efficiency for producing milk but with an associated reduced fertility. Embryo loss is the greatest factor contributing to the failure of a cow to conceive. The extent and timing of embryo loss indicates that 70% to 80% of this loss occurs in the first 2 weeks after artificial insemination (AI). This is the period when a number of critical phases in embryo development occur and where protein accretion, substrate utilization and embryo metabolism increase dramatically. During this time the early embryo is completely dependent on the oviduct and uterine environment for its survival and it is likely that the embryo requires an optimal uterine environment to ensure normal growth and viability. There is increasing evidence of an association between the concentration of systemic progesterone and early embryo loss and that progesterone supplementation of cows, particularly those with low progesterone, can reduce this loss. While progesterone is known to affect uterine function and embryo growth, little is known about the uterus during the period of early embryo loss and how this is affected by changes in the concentration of systemic progesterone. The expression of uterine genes encoding the transport protein retinol binding protein (RBP) and the gene for folate binding protein (FBP) appear to be sensitive to changes in systemic progesterone, particularly during the early luteal phase of the cycle. Uterine concentrations of proteins also seem to be regulated by stage of cycle; however, their relationship with the systemic concentration of progesterone is unclear. There is an urgent need to characterize the uterine environment from a functional perspective during the early part of the luteal phase of the cycle, particularly in the high-producing cow, in order to understand the factors contributing to early embryo loss and in order to devise strategies to minimize or reduce this loss.

Expression of nuclear progesterone receptor and progesterone receptor membrane components 1 and 2 in the oviduct of cyclic and pregnant cows during the post-ovulation period

BACKGROUND

Progesterone (P4) may modulate oviductal functions to promote early embryo development in cattle. In addition to its nuclear receptor (PR), P4 may mediate its actions through P4 receptor membrane component 1 (PGRMC1) and its relative, PGRMC2. Two successive experiments were undertaken to characterise the expression of PR, PGRMC1 and PGRMC2 in the bovine oviduct during the post-ovulation period, and to relate their expression to the presence of an embryo, the proximity of the CL and to the region of the oviduct.

METHODS

In the first experiment (Exp. I), whole oviduct sections were collected from Holstein cows at Day 1.5, Day 4 and Day 5 post-ovulation (n = 2 cows per stage). The expression of PR, PGRMC1 and PGRMC2 was studied in the ampulla and isthmus by RT-PCR, western-blot and immunohistochemistry. In Exp. II, oviduct epithelial cells were collected from cyclic and pregnant Charolais cows (n = 4 cows per status) at Day 3.5 post-ovulation and mRNA expression of PR, PGRMC1 and PGRMC2 was examined in the ampulla and isthmus by real-time quantitative PCR.

RESULTS

In Exp. I, PR, PGRMC1 and PGRMC2 were expressed in all oviduct samples. PGRMC1 was mainly localised in the luminal epithelium whereas PR and PGRMC2 were localised in the epithelium as well as in the muscle and stroma layers of the oviduct. The expression was primarily nuclear for PR, primarily cytoplasmic for PGRMC1 and both nuclear and cytoplasmic for PGRMC2. In Exp. II, mRNA levels for PR, PGRMC1 and PGRMC2 were not affected by either the pregnancy status or the side relative to the CL. However, the expression of PR and PGRMC2 varied significantly with the region of the oviduct: PR was more highly expressed in the isthmus whereas PGRMC2 was more highly expressed in the ampulla.

CONCLUSIONS

This is the first evidence of PGRMC2 expression in the bovine oviduct. Our findings suggest that P4 regulates the functions of the bovine oviduct in a region-specific manner and through both classical and non classical pathways during the post-ovulation period.

Effect of asynchronous transfer on bovine embryonic development and relationship with early cycle uterine proteome profiles

The uterus provides the nurturing environment that supports the growth of the early preimplantation bovine conceptus. To determine critical time points of uterine influence, in vitro-produced Day 7 blastocysts were transferred into synchronous (Day 7) uteri and asynchronous uteri (Days 5 or 9). Embryo growth was evaluated 7 and 15 days after transfer and compared with that of embryos generated by AI. Conceptuses recovered from asynchronous Day 9 transfers were fourfold larger than synchronous transfer or gestational Day 14 AI conceptuses; by 15 days after transfer, differences were less marked. Two-dimensional gel electrophoresis was used to compare the histotroph protein composition of uterine luminal flushings (ULF) on Days 5 and 9 after oestrous to determine any protein differences that would promote embryo growth. The ULF were collected by serially flushing the uteri of the same heifers and mature cows at different times of the cycle. Ten proteins that differed in abundance between Day 5 and 9 were identified by mass spectrometry. Three, namely phosphoserine aminotransferase 1, purine nucleoside phosphorylase and aldose reductase, were verified by western blot analysis as more abundant on Day 9 (P < 0.002). Myostatin was present in only in Day 9 ULF, whereas tissue inhibitor of matrix metalloproteinase 2 (TIMP2) and legumain were only detected in Day 14 ULF. Although mature cows had lower progesterone concentrations on Days 5 and 14 (P < 0.05) and tended to have less TIMP2 than heifer groups, no other protein differences were detected. Thus, the embryo growth-enhancing environment on Day 9 was associated with temporal changes in the expression of several proteins of the histotroph.

Relationship between late embryonic mortality and the increase in plasma advanced oxidised protein products (AOPP) in dairy cows

The involvement of protein oxidation in embryonic mortality (EM) has been poorly investigated in cows. Advanced oxidation protein products (AOPP) are markers of protein oxidation generated by activated neutrophils and involved in inflammation. The aim of this work was to study AOPP in cow plasma and their relationship with late EM. The outcomes of 158 artificial inseminations (AI) were examined in 72 cows, which were classified ex post on the basis of blood progesterone and pregnancy-associated glycoprotein concentrations and clinical confirmation of pregnancy into the following categories: (1) positive (AI+, resulted in pregnancy, n=58), (2) negative (AI-, did not result in pregnancy, n=86) and (3) embryonic mortality (EM, n=14). Plasma protein fractions, malondialdehyde (MDA), total glutathione and AOPP were measured at AI (Day 0) and on Days 15, 28, 35, 45 and 60. MDA was significantly higher in EM than AI+ and AI- animals on Day 45, and than AI+ animals on Day 60 (P<0.05). Mean plasma AOPP concentrations were significantly higher in the EM group (P<0.01) and the ratio of AOPP:albumin was significantly higher in the EM group on Days 15, 28, 45 and 60 (P<0.05). Based on the temporal pattern of the AOPP:albumin ratio, we propose that oxidative stress is implicated in and may possibly be a cause of EM.

Effect of elevated circulating progesterone concentration on bovine blastocyst development and global transcriptome following endoscopic transfer of in vitro produced embryos to the bovine oviduct

Elevated concentrations of circulating progesterone in the immediate postconception period have been associated with an increase in embryonic growth rate, interferon-tau production, and pregnancy rate in cattle and sheep. Much of this effect is likely mediated via downstream effects of progesterone-induced changes in gene expression in the uterine tissues. Using state-of-the-art endoscopic techniques, this study examined the effect of elevated progesterone on the development of in vitro produced bovine zygotes transferred to the oviducts of heifers with high or normal circulating progesterone concentrations and on the transcriptome of blastocysts developing under such conditions. Simmental heifers (n = 34) were synchronized using a controlled internal drug release (CIDR) device for 8 days, with a prostaglandin F(2 alpha) analogue administered 3 days before removal of the CIDR device. Only animals exhibiting a clear standing estrus (Day 0) were used. To produce animals with divergent progesterone concentrations, half of the animals received a progesterone-releasing intravaginal device (PRID) on Day 3 of the estrous cycle; the PRID was left in place until embryo recovery. All animals were sampled for blood daily from Day 0 to Day 7. Cleaved embryos were transferred by endoscopy to the ipsilateral oviduct of each recipient on Day 2 and then recovered by nonsurgically flushing the oviduct and the uterus on Day 7. The number of embryos developing to the blastocyst stage was recorded at recovery and following overnight culture in vitro. Potential effects of elevated progesterone on transcript abundance were examined using the Affymetrix GeneChip Bovine Genome Array. Insertion of a PRID on Day 3 resulted in a significant elevation of progesterone concentration (P < 0.05) from Day 3.5 until Day 6. Elevated progesterone did not affect the proportion of embryos developing to the blastocyst stage. Genomewide gene expression analysis identified 194 differentially expressed genes between embryos collected from heifers with normal or elevated progesterone, and quantitative real-time PCR validation with a subset of selected genes and an independent sample confirmed the microarray results. Interaction network analysis indicated a significant interaction between progesterone-regulated genes in the blastocyst and in the maternal endometrium. These results suggest that elevated concentrations of progesterone do not affect the ability of the early embryo to reach the blastocyst stage in vivo but do result in subtle changes to the transcriptome of the embryo that may be associated with advanced elongation posthatching.

Progesterone and conceptus elongation in cattle: a direct effect on the embryo or an indirect effect via the endometrium?

The steroid hormone progesterone (P4) plays a key role in the reproductive events associated with pregnancy establishment and maintenance. High concentrations of circulating P4 in the immediate post-conception period have been associated with an advancement of conceptus elongation, an associated increase in interferon-τ production and higher pregnancy rates in cattle. Using in vitro and in vivo models and ∼8500 bovine oocytes across six experiments, the aim of this study was to establish the route through which P4 affects bovine embryo development in vitro and in vivo. mRNA for P4 receptors was present at all stages of embryo development raising the possibility of a direct effect of P4 on the embryo. Exposure to P4 in vitro in the absence or presence of oviduct epithelial cells did not affect the proportion of embryos developing to the blastocyst stage, blastocyst cell number or the relative abundance of selected transcripts in the blastocyst. Furthermore, exposure to P4 in vitro did not affect post-hatching elongation of the embryo following transfer to synchronized recipients and recovery on Day 14. By contrast, transfer of in vitro derived blastocysts to a uterine environment previously primed by elevated P4 resulted in a fourfold increase in conceptus length on Day 14. These data provide clear evidence to support the hypothesis that P4-induced changes in the uterine environment are responsible for the advancement in conceptus elongation reported previously in cattle and that, interestingly, the embryo does not need to be present during the period of high P4 in order to exhibit advanced elongation.

Differential effects of exogenous progesterone administration at different stages of the luteal phase on endogenous oestradiol concentration in cows

We have investigated the effects administering exogenous progesterone, via insertion of a controlled internal drug release (CIDR) for 4 days, from either day 5 or day 12 of the oestrous cycle on plasma oestradiol concentrations. In study 1, in which progesterone was administered from day 5, measurement of plasma oestradiol in daily samples revealed a significant (p < 0.001) decrease in peripheral oestradiol concentration. In contrast, in study 2, similar administration of progesterone from day 12 had no effect on plasma oestradiol concentration. In study 3, collection of hourly samples following progesterone treatment on day 5 revealed peak progesterone concentrations within 1 h of CIDR insertion and nadir oestradiol concentrations within 4 h. The results demonstrate that treatment with progesterone early in the luteal phase causes a rapid inhibition of oestradiol secretion, while later treatment does not. While improvements in pregnancy rate following progesterone treatment at this time have traditionally been attributed to increases in progesterone, the potential involvement of decreased oestradiol secretion has often been overlooked.

Effect of meloxicam treatment during early pregnancy in Holstein heifers

We previously reported that administration of flunixin meglumine two times at a critical stage approaching pregnancy recognition associated with maintenance of the corpus luteum (CL) increased early embryo survival and pregnancy rate via an additive antiluteolytic effect with the conceptus [Vet Rec 160 (2007) 404]. In this study, the objective was to determine if a single administration of meloxicam, a non-steroid anti-inflammatory drug with a longer half-life, could be used instead of flunixin meglumine. This would avoid repeated injections in heifers following insemination at a critical stage to increase pregnancy rate due to its inhibitory effect on prostaglandin F(2alpha) synthesis. Eighty-five, 15- to 18-month-old Holstein heifers were synchronized, and following insemination (day 0) heifers were assigned to receive subcutaneous meloxicam injection (0.5 mg/kg; n = 37) on the afternoon of day 15 or were untreated as a control (n = 48). Pregnancy rates were defined as the percentage of heifers inseminated that were diagnosed pregnant by ultrasound between days 31 and 38 after artificial insemination. Effect of the treatment on pregnancy rates was analysed by chi-square test. Meloxicam treatment on day 15 after insemination dramatically decreased pregnancy rates in the heifers (52%; 25 of 48 in the control group vs 24.3%; 9 of 37 in the meloxicam-treated group; p < 0.01). This result indicates that administration of meloxicam at the time associated with pregnancy recognition processes to maintain the CL was harmful to the pregnancy even though the drug is considered to be safe during pregnancy in cattle.

Corpus luteum-endometrium-embryo interactions in the dairy cow: underlying mechanisms and clinical relevance

Conception rates of dairy cows are currently declining at an estimated 1% every year. Approximately, 35% of embryos fail to prevent luteolysis during the first three weeks of gestation. Interactions between the corpus luteum, endometrium and embryo are critical to the successful establishment of pregnancy and inadequacies will result in the mortality of the embryo. For example, as little as a one day delay in the post-ovulatory rise of progesterone has serious consequences for embryo development and survival. Recently, we found that LH support, degree of vascularization and luteal cell steroidogenic capacity were not the major factors responsible for this luteal inadequacy, but are nevertheless essential for luteal development and function. Progesterone acting on its receptor in the endometrium stimulates the production of endometrial secretions on which the free-living embryo is dependent. However, their exact composition and effects of inadequate progesterone remains to be determined. The embryo is recognized through its secretion of interferon tau (IFNT), which suppresses luteolytic pulses of prostaglandin F(2 alpha). In the cow, it is most likely that IFNT inhibits oxytocin receptor up-regulation directly and does not require the prior inhibition of oestrogen receptor alpha (ESR1). Unravelling the precise luteal-endometrium and embryo interactions is essential for us to understand pregnancy establishment and development of strategies to reverse the declining fertility of dairy cows.