Effects of time of progesterone supplementation on embryo development and interferon-tau production in the cow

Transcriptomic analysis of the bovine endometrium: What is required to establish uterine receptivity to implantation in cattle?

In cattle, the majority of pregnancy loss can be attributed to early embryonic loss which occurs prior maternal recognition of pregnancy on Day 16 (Day 0 = ovulation). During this time, carefully orchestrated spatio-temporal alterations in the transcriptomic profile of the endometrium are required to drive conceptus elongation, via secretions from the endometrium (termed histotroph) and establish uterine receptivity to implantation. The two main modulators of these processed are progesterone (P4) and the pregnancy recognition signal interferon tau (IFNT). Altered concentrations of P4 in circulation mediate its effects via the endometrium and have been associated with different rates of conceptus elongation in cattle. Transcriptomic analysis of the endometrium has shown that modulation of circulating P4 alters endometrial expression of genes that can contribute to histotroph composition, which is beneficial (when P4 is supplemented) or detrimental (when P4 is reduced) to the developing conceptus. In addition, down-regulation of the progesterone receptor, required to establish uterine receptivity, is altered in the endometrium of heifers with altered P4 concentrations. IFNT, a type 1 interferon, also significantly impacts on the endometrial transcriptome. It induces the expression of a large number of classical interferon stimulated genes as early as Day 15 of pregnancy. In summary, the successful establishment of pregnancy in cattle requires a sequence of key events to ensure appropriate maternally derived secretions, establish uterine receptivity to implantation as well as an adequate endometrial response to IFNT production.

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.

Select nutrients, progesterone, and interferon tau affect conceptus metabolism and development

Interferon tau (IFNT), a novel multifunctional type I interferon secreted by trophectoderm, is the pregnancy recognition signal in ruminants that also has antiviral, antiproliferative, and immunomodulatory bioactivities. IFNT, with progesterone, affects availability of the metabolic substrate in the uterine lumen by inducing expression of genes for transport of select nutrients into the uterine lumen that activate mammalian target of rapamycin (mTOR) cell signaling responsible for proliferation, migration, and protein synthesis by conceptus trophectoderm. As an immunomodulatory protein, IFNT induces an anti-inflammatory state affecting metabolic events that decrease adiposity and glutamine:fructose-6-phosphate amidotransferase 1 activity, while increasing insulin sensitivity, nitric oxide production by endothelial cells, and brown adipose tissue in rats. This short review focuses on effects of IFNT and progesterone affecting transport of select nutrients into the uterine lumen to stimulate mTOR cell signaling required for conceptus development, as well as effects of IFNT on the immune system and adiposity in rats with respect to its potential therapeutic value in reducing obesity.

Endometrial response of beef heifers on day 7 following insemination to supraphysiological concentrations of progesterone associated with superovulation

Ovarian stimulation is a routine procedure in assisted reproduction to stimulate the growth of multiple follicles in naturally single-ovulating species including cattle and humans. The aim of this study was to analyze the changes induced in the endometrial transcriptome associated with superovulation in cattle and place these observations in the context of our previous data on changes in the endometrial transcriptome associated with elevated progesterone (P4) concentrations within the physiological range and those changes induced in the embryo due to superovulation. Mean serum P4 concentrations were significantly higher from day 4 to day 7 in superovulated compared with unstimulated control heifers (P < 0.05). Between-group analysis revealed a clear separation in the overall transcriptional profile of endometria from unstimulated control heifers (n = 5) compared with superovulated heifers (n = 5). This was reflected in the number of differentially expressed genes (DEGs) identified between the two groups with 795 up- and 440 downregulated in superovulated endometria. Ten times more genes were altered by superovulation (n = 1,234) compared with the number altered due to elevated P4 within physiological ranges by insertion of a P4-releasing intravaginal device (n = 124) with only 22 DEGs common to both models of P4 manipulation. Fewer genes were affected by superovulation in the embryo compared with the endometrium, (443 vs. 1,234 DEGs, respectively), and the manner in which genes were altered was different with 64.5% of genes up- and 35.5% of genes downregulated in the endometrium, compared with the 98.9% of DEGs upregulated in the embryo. In conclusion, superovulation induces significant changes in the transcriptome of the endometrium which are distinct from those in the embryo.

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.

Mechanistic mammalian target of rapamycin (MTOR) cell signaling: effects of select nutrients and secreted phosphoprotein 1 on development of mammalian conceptuses

Morphological differentiation of uterine glands in mammals is a postnatal event vulnerable to adverse effects of endocrine disruptors. Exposure of ewe lambs to a progestin from birth to postnatal day 56 prevents development of uterine glands and, as adults, the ewes are unable to exhibit estrous cycles or maintain pregnancy. Uterine epithelia secrete proteins and transport nutrients into the uterine lumen necessary for conceptus development, pregnancy recognition signaling and implantation, including arginine and secreted phosphoprotein 1 (SPP1). Arginine can be metabolized to nitric oxide and to polyamines or act directly to activate MTOR cell signaling to stimulate proliferation, migration, and mRNA translation in trophectoderm cells. SPP1 binds αvβ3 and α5β1 integrins and induces focal adhesion assembly, adhesion and migration of conceptus trophectoderm cells during implantation. Thus, arginine and SPP1 mediate growth, migration, cytoskeletal remodeling and adhesion of trophectoderm essential for pregnancy recognition signaling and implantation.

Relationship between quantity of IFNT estimated by IFN-stimulated gene expression in peripheral blood mononuclear cells and bovine embryonic mortality after AI or ET

BACKGROUND

Interferon tau (IFNT), which is secreted into the uterine cavity during the maternal recognition period (MRP), is a key factor for establishment of pregnancy. The present study aims to clarify the relationship between the ability of a bovine conceptus to produce IFNT during the MRP and the conceptus's ability to establish pregnancy.

METHODS

In the first experiment, IFNT (0, 500, or 1000 micrograms) was administered into the uterine horn ipsilateral to the CL 16 or 17 d after standing estrus, and mRNA levels of IFN-stimulated gene 15-kDa protein (ISG15) and Mx2 in peripheral blood mononuclear cells (PBMCs) were determined. In the second experiment, we investigated ISG15 mRNA expression in PBMCs during the MRP in cattle after either artificial insemination (AI) or embryo transfer (ET).

RESULTS

Intrauterine administration of IFNT stimulated ISG15 and Mx2 gene expressions in PBMCs in cattle, and there was a positive correlation between the expressions of peripheral markers and the quantity of IFNT administered. In pregnant and normal interestrous interval (< 25 d) cattle (nIEI cattle), expression levels of the ISG15 gene showed similar patterns after AI and ET, and ISG15 mRNA expression was increased in pregnant cattle but unchanged in nIEI cattle. In contrast, ISG15 gene expression in extended interestrous interval (greater than or equal to 25 d) cattle (eIEI cattle) differed after ET compared with AI. In eIEI cattle after ET, ISG15 gene expression increased, such that the value on day 18 was intermediate between those of pregnant and nIEI cattle. In eIEI cattle after AI, ISG15 gene expression did not increase throughout the observation period.

CONCLUSIONS

The results of the current study indicate that the quantity of conceptus-derived IFNT can be estimated by measuring ISG15 mRNA levels in PBMCs from cattle. Using this approach, we demonstrate that ISG15 gene expression during the MRP in eIEI cattle differed after ET compared with AI. In addition, the modest increase in ISG15 gene expression in eIEI cattle after ET suggests that late embryo losses were due to delayed or insufficient growth of the conceptus during the MRP in cattle.

Interaction of the conceptus and endometrium to establish pregnancy in mammals: role of interleukin 1β

Implantation and the establishment of pregnancy in mammals involves an intricate interplay of hormones, cytokines, growth factors, proteins, lipids, ions and the extracellular matrix between the uterine epithelium, stroma, immune cells and the conceptus trophectoderm. The divergent nature of implantation in the mouse, human and pig provides not only an interesting contrast in the establishment of pregnancy and early embryonic development but also intriguing similarities with regard to early endometrial-conceptus signaling. An interesting pro-inflammatory cytokine expressed in a number of mammalian species during the period of implantation is interleukin-1β (IL1B). The presence of IL1B might be involved with immunotolerance at the maternal-placental interface and has been proposed as one of the mediators in placental viviparity. The production of IL1B and other proinflammatory cytokines might play a role in establishing pregnancy through modulation of the nuclear factor kappa-B (NFKB) system in a number of species. A model for the regulation of cellular progesterone receptor expression and NFKB activation for endometrial receptivity and conceptus attachment is continuing to evolve and is discussed in the present review.

The use of endocrine treatments to improve pregnancy rates in cattle

Reproduction is critical for the success of both dairy and beef cattle production. Inadequate reproduction impairs profitability by compromising production, delaying genetic progress and increasing expenses. A major impediment to the use of artificial insemination (AI) is the ability to detect oestrus for optimum timing of breeding. However, increased understanding of the bovine oestrous cycle has led to the development of reproductive programmes that allow precise synchrony of follicle development, luteal regression and ovulation. The advent of timed-AI protocols revolutionised reproductive management in dairy and beef herds. It allows for AI at a more desired time post partum despite oestrous cyclicity. It also allows for pre-determined re-insemination of cows diagnosed as not pregnant. In subfertile cows, such as the post partum, anoestrous beef cow and the high-producing dairy cow, strategic hormone supplementation has been used to overcome hormone deficiencies and improve pregnancy rates. Several physiological windows have been identified to optimise fertility in synchronisation programmes and they include, but are not limited to, follicle turnover, synchrony of follicular development, length of dominance, progesterone concentrations during development of the ovulatory follicle, luteal regression, peri-ovulatory steroid concentrations, length of pro-oestrus, synchrony of ovulation and AI, and progesterone rise after ovulation.

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.

Intrafollicular conditions as a major link between maternal metabolism and oocyte quality: a focus on dairy cow fertility

Reduced oocyte and embryo quality are recognised as major factors in the problem of disappointing fertility in high producing dairy cows. This review aims to shed more light on the importance of the intrafollicular environment in the subfertility problem in dairy cows. Metabolic disturbances associated with negative energy balance (NEB) early postpartum are associated with ovarian dysfunction. Changes in the growth pattern of the ovarian follicle during a period of NEB can indirectly affect oocyte quality. Furthermore, a maternal metabolic disorder (linked with NEB or nutritionally induced) may alter the endocrine and biochemical composition of the follicular fluid, the micro-environment of the growing and maturing female gamete. The maturing oocyte is very sensitive to any perturbation in its direct environment and in vitro maturation models revealed that some of these metabolic changes reduce the oocyte’s developmental competence. Also, embryo quality is significantly reduced due to maturation in adverse conditions. Well balanced and timed oocyte metabolism and gene expression are crucial to safeguard an optimal oocyte development. In that perspective, metabolome and transcriptome parameters of the oocyte may serve to predict reproductive success rates. Finally, there is growing evidence that adverse conditions for oocyte growth and maturation may also jeopardise the health and performance of the offspring.

Endometrial gene expression during early pregnancy differs between fertile and subfertile dairy cow strains

A receptive uterine environment is a key component in determining a successful reproductive outcome. We tested the hypothesis that endometrial gene expression patterns differ in fertile and subfertile dairy cow strains. Twelve lactating dairy cattle of strains characterized as having fertile (n = 6) and subfertile (n = 6) phenotypes underwent embryo transfer on day 7 of the reproductive cycle. Caruncular and intercaruncular endometrial tissue was obtained at day 17 of pregnancy, and microarrays used to characterize transcriptional profiles. Statistical analysis of microarray data at day 17 of pregnancy revealed 482 and 1,021 differentially expressed transcripts (P value < 0.05) between fertile and subfertile dairy cow strains in intercaruncular and caruncular tissue, respectively. Functional analysis revealed enrichment for several pathways involved in key reproductive processes, including the immune response to pregnancy, luteolysis, and support of embryo growth and development, and in particular, regulation of histotroph composition. Genes implicated in the process of immune tolerance to the embryo were downregulated in subfertile cows, as were genes involved in preventing luteolysis and genes that promote embryo growth and development. This study provides strong evidence that the endometrial gene expression profile may contribute to the inferior reproductive performance of the subfertile dairy cow strain.

Uterine histotroph and conceptus development: select nutrients and secreted phosphoprotein 1 affect mechanistic target of rapamycin cell signaling in ewes

Interferon tau (IFNT), the pregnancy recognition signal in ruminants, abrogates the uterine luteolytic mechanism to ensure maintenance of function for the corpora lutea to produce progesterone (P4). IFNT also suppresses expression of classical IFN-stimulated genes by uterine lumenal epithelium (LE) and superficial glandular (sGE) epithelium but, acting in concert with progesterone, affects expression of a multitude of genes critical to growth and development of the conceptus. The LE and sGE secrete proteins and transport nutrients into the uterine lumen necessary for conceptus development, pregnancy recognition signaling, and implantation. Secretions include arginine and secreted phosphoprotein 1 (SPP1). Arginine can be metabolized to nitric oxide and to polyamines or act directly to activate the mechanistic target of rapamycin cell signaling pathway to stimulate proliferation, migration, and mRNA translation in trophectoderm cells. SPP1 binds alphavbeta3 and alpha5beta1 integrins to induce focal adhesion assembly, adhesion, and migration of conceptus trophectoderm cells during implantation. Thus, arginine and SPP1 mediate growth, migration, cytoskeletal remodeling, and adhesion of trophectoderm essential for pregnancy recognition signaling and implantation. This minireview focuses on components of histotroph that affect conceptus development in the ewe.

Recent advances in the synchronization of estrus and ovulation in dairy cows

Synchronization programs have become standard components in the current breeding management of cows in the dairy herds of most dairy industries. Many are based on protocols that allow timed inseminations (TAI) so as to circumvent the practical difficulties associated with estrus detection. These difficulties are exacerbated in modern herds of high producing cows either because of increasing herd size in which individual animal monitoring is difficult and often subjective, or because small intensively managed herds are milked in robotic systems that minimize animal: staff interactions. Additional reasons arise from high producing cows having less obvious symptoms of estrus, partly because of housing systems combined with intensive feeding and milking, partly because of higher metabolic clearance rates of reproductive hormones like estradiol and partly because of the increasing prevalence of prolonged post-partum anestrus and reproductive tract pathology. The most recently developed programs include protocols for resynchronization following first or subsequent inseminations. These re-synchronization protocols may involve selected forms of hormonal intervention during the diestrous and pro-estrous periods following TAI, or following pregnancy diagnosis by ultrasound from 28 days after TAI. The latter form of re-synchronization has become increasingly important with the recognition that late embryonic/early foetal death has become a major factor compromising the reproductive performance of high producing Holstein cows in many dairy industries. Although cows detected in estrus without any hormonal treatment before insemination have higher conception rates than those inseminated following synchronization and TAI, the low detection rates combined with embryonic death means that intervals from calving to conception (days open) are usually less when synchronization programs have been successfully implemented. One of the significant factors affecting a program's success is the compliance rate that may sometimes be less than 70%. Almost all programs involve strategically timed injections of prostaglandin F2alpha (PGF) and gonadotropin releasing hormone (GnRH). Injections of an estradiol ester and progesterone supplementation per vaginum may be included in some programs. The basic program is the "Ovsynch" regimen. Numerous variations have been tested and developed. Many involve increasingly complex protocols that increase the risk of non-compliance, none has consistently achieved conception rates that exceed 40% and few have reduced the incidence of embryonic death. These synchronization programs are the best that are currently available. They have not been able to overcome the consequences of lowered fertility associated with high levels of milk yield, forms of nutrition and environmental factors like heat stress that have profound effects on the physiology and metabolism of the high producing dairy cow.

The effect of elevated progesterone and pregnancy status on mRNA expression and localisation of progesterone and oestrogen receptors in the bovine uterus

To investigate the effects of pregnancy or post-ovulatory progesterone (P4) supplementation on the expression of oestrogen and P4 receptors (ESRs and PGRs) in the bovine uterus, heifers (n=263) were randomly assigned to the following treatments: i) cyclic, normal P4; ii) cyclic, high P4; iii) pregnant, normal P4; and iv) pregnant, high P4 on days 5, 7, 13 and 16 of pregnancy/oestrous cycle. Elevated P4 was achieved through P4-releasing intravaginal device insertion on day 3 after oestrus, resulting in increased concentrations from day 3.5 to 8 (P<0.05) in the high groups than in the normal groups. Irrespective of treatment, PGR and ESR1 mRNA expressions were highest on days 5 and 7 and decreased on day 13 (P<0.05), while ESR2 mRNA expression increased on day 7 (P<0.05) and similar levels were maintained within the normal P4 groups subsequently. Expression in the high P4 groups decreased on day 13 (P<0.05). PGR-AB and PGR-B protein expressions were high in the luminal and superficial glands on days 5 and 7, but by day 13, expression had declined to very low or undetectable levels and high P4 concentration tended to decrease or decreased significantly (P<0.05) the expression in these regions on days 5 and 7. ESR1 protein expression was high, with no treatment effect. ESR2 protein was also highly expressed, with no clear effect of treatment. In conclusion, early post-ovulatory P4 supplementation advances the disappearance of PGR protein from the luminal epithelium on days 5 and 7, and decreases ESR2 mRNA expression during the mid-luteal phase, but has no effect on PGR or ESR1 mRNA expression.

Developmental kinetics and gene expression in male and female bovine embryos produced in vitro with sex-sorted spermatozoa

Using bovine embryos generated in vitro from IVF with X-sorted, Y-sorted and unsorted spermatozoa, we compared the kinetics of male and female embryo development and gene expression between male and female blastocysts. Bovine in vitro-matured oocytes (n = 8858) were fertilised with spermatozoa from each of three different bulls (X-sorted, Y-sorted or unsorted spermatozoa depending on the experiment). The cleavage rate was assessed 24, 27, 30, 33, 36, 40, 44 and 48 h post insemination (h.p.i.) and blastocyst development was recorded on Days 6-9. The relative mRNA abundance of nine genes (GSTM3, DNTM3A, PGRMC1, TP53, BAX, COX2, IGF2R, AKR1B1 and PLAC8) was analysed in male and female Day 7 blastocysts produced with sorted and unsorted spermatozoa from one bull. Cumulative cleavage rate and blastocyst yield were significantly higher in the unsorted group compared with the X- or Y-sorted group from the same bull (P < or = 0.05). Although differences existed between bulls in terms of cleavage rate, no differences were observed in cleavage rate between X- and Y-sorted spermatozoa within a bull. The blastocyst yield was significantly higher only for Bull 3 when the Y-sorted spermatozoa were used (27.1+2.8 v. 19.1+1.4 for Y- and X-sorted spermatozoa, respectively; P < 0.05). There were no differences in the mRNA abundance of the nine genes analysed between embryos of the same sex produced with sorted or unsorted spermatozoa. However, significant differences in polyA mRNA abundance were observed between male and female blastocysts for three genes (GSTM3, DNMT3A and PGRMC1; P < or = 0.05). In conclusion, the use of sorted rather than unsorted spermatozoa in IVF significantly delays the onset of first cleavage. Differences were noted between bulls, but not between X- and Y-sorted spermatozoa, and although no differences were found in terms of the mRNA abundance of the nine genes tested between sorted and unsorted spermatozoa, sex-related differences were found in the case of three genes.

Pregnancy recognition and abnormal offspring syndrome in cattle

Development of the post-hatching conceptus in ruminants involves a period of morphological expansion that is driven by complex interactions between the conceptus and its intrauterine environment. As a result of these interactions, endometrial physiology is altered, leading to establishment of the pregnancy and continued development of the placenta. Disruption of normal fetal and placental development can occur when embryos are exposed to manipulations in vitro or when inappropriate endocrine sequencing occurs in vivo during the pre- and peri-implantation periods. The present review addresses the development of the post-hatching bovine conceptus, its interactions with the maternal system and changes in development that can occur as a result of in vivo and in vitro manipulations of the bovine embryo.

Short communication: Effects of the progesterone receptor variants on fertility traits in cattle

The progesterone receptor (PGR) gene is a key factor in the initiation and maintenance of pregnancy and in embryo development. Currently, it is unknown what variants of the PGR gene are related to fertility traits in cattle. Identification of such variants would allow the implementation of marker-assisted selection in breeding schemes. The objective of this study was to investigate the association of single nucleotide polymorphisms (SNP) of PGR with fertility traits in Holstein dairy cattle. An in vitro fertilization system was used to maximize the efficiency of the identification of genetic factors affecting fertility. This in vitro fertilization system would allow the assessment of fertilization and embryonic survival rates independently of influences from the uterine environment. A total of 5,566 fertilization attempts were performed, and a total of 3,679 embryos were produced using oocytes from 324 Holstein cows and semen from 10 Holstein bulls. Sequencing of pooled DNA samples from ovaries revealed an SNP (G/C) in intron 3 of PGR. A generalized linear model was used to analyze the association of this SNP with fertilization and embryonic survival rates for each ovary. Oocytes obtained from CC ovaries showed a 61% fertilization rate, compared with 68 and 69% for GC and GG ovaries, respectively. The survival rate of embryos produced from GG ovaries was 5 and 6% higher than that of GC and CC ovaries . These results indicate that the PGR SNP could be used in marker-assisted selection breeding programs in Holstein dairy cattle.

Discovery of candidate genes and pathways in the endometrium regulating ovine blastocyst growth and conceptus elongation

Establishment of pregnancy in ruminants requires blastocyst growth to form an elongated conceptus that produces interferon tau, the pregnancy recognition signal, and initiates implantation. Blastocyst growth and development requires secretions from the uterine endometrium. An early increase in circulating concentrations of progesterone (P4) stimulates blastocyst growth and elongation in ruminants. This study utilized sheep as a model to identify candidate genes and regulatory networks in the endometrium that govern preimplantation blastocyst growth and development. Ewes were treated daily with either P4 or corn oil vehicle from day 1.5 after mating to either day 9 or day 12 of pregnancy when endometrium was obtained by hysterectomy. Microarray analyses revealed many differentially expressed genes in the endometria affected by day of pregnancy and early P4 treatment. In situ hybridization analyses revealed that many differentially expressed genes were expressed in a cell-specific manner within the endometrium. The Database for Annotation, Visualization, and Integrated Discovery (DAVID) was used to identify functional groups of genes and biological processes in the endometrium that are associated with growth and development of preimplantation blastocysts. Notably, biological processes affected by day of pregnancy and/or early P4 treatment included lipid biosynthesis and metabolism, angiogenesis, transport, extracellular space, defense and inflammatory response, proteolysis, amino acid transport and metabolism, and hormone metabolism. This transcriptomic data provides novel insights into the biology of endometrial function and preimplantation blastocyst growth and development in sheep.

Several fibroblast growth factors are expressed during pre-attachment bovine conceptus development and regulate interferon-tau expression from trophectoderm

The trophectoderm-derived factor interferon tau (IFNT) maintains the uterus in a pregnancy-receptive state in cattle and sheep. Fibroblast growth factors (FGFs) are implicated in regulatingIFNTexpression and potentially other critical events associated with early conceptus development in cattle. The overall objectives of this work were to identify the variousFGFsand FGF receptors (FGFRs) expressed in elongating pre-attachment bovine conceptuses and determine if these FGFs regulate conceptus development and/or mediate IFNT production.In vitro-derived bovine blastocysts andin vivo-derived elongated conceptuses collected at day 17 of pregnancy express at least fourFGFRsubtypes (R1c,R2b,R3c,R4). In addition, transcripts forFGF1,2, and10but notFGF7are present in elongated bovine conceptuses. The expression pattern ofFGF10most closely resembled that ofIFNT, with both transcripts remaining low in day 8 and day 11 conceptuses and increasing substantially in day 14 and day 17 conceptuses. Supplementation with recombinant FGF1, 2 or 10 increasedIFNTmRNA levels in bovine trophectoderm cells and bovine blastocysts and increased IFNT protein concentrations in trophectoderm-conditioned medium. Blastocyst development was not affected by any of the FGFs. In summary, at least four FGFRs reside in pre- and peri-attachment bovine conceptuses. Moreover, conceptuses express at least three candidate FGFs during elongation, the time of peakIFNTexpression. These findings provide new insight for how conceptus-derived factors such as FGF1, 2, and 10 may controlIFNTexpression during early pregnancy in cattle.

First service pregnancy rates following post-AI use of HCG in Ovsynch and Heatsynch programmes in lactating dairy cows

Lactating dairy cows (n = 667) at random stages of the oestrous cycle were assigned to either ovsynch (O, n = 228), heatsynch (H, n = 252) or control (C, n = 187) groups. Cows in O and H groups received 100 microg of GnRH agonist, i.m. (day 0) starting at 44 +/- 3 days in milk (DIM), and 500 microg of cloprostenol, i.m. (day 7). In O group, cows received 100 microg of GnRH (day 9) and were artificially inseminated without oestrus detection 16-20 h later. In H group, cows received 1 mg oestradiol benzoate (EB) i.m., 24 h after the cloprostenol injection and were artificially inseminated without oestrus detection 48-52 h after the EB injection. Cows in C group were inseminated at natural oestrus. On the day of artificial insemination (AI), cows in all groups were assigned to subgroups as follows: human Chorionic Gonadotrophin (O-hCG) (n = 112), O-saline (n = 116), H-hCG (n = 123), H-saline (n = 129), C-hCG (n = 94) and C-saline (n = 93) subgroups. Cows in hCG and saline subgroups received 3000 IU hCG i.m. and or 10 ml saline at day 5 post-AI (day 15), respectively. Pregnancy status was assessed by palpation per rectum at days 40 to 45 after AI. The logistic regression model using just main effects of season (summer and winter), parity (primiparous and pluriparous), method(1) (O, H and C) and method(2) (hCG and saline) showed that all factors, except method(1), were significant. Significant effects of season (p < 0.01), hCG and parity (p < 0.01), and a trend of parity and season (p < 0.1) were detected. A clear negative effect of warm period on first service pregnancy rate was noted (p < 0.01). The pregnancy rate was the lowest in the H protocol during warm period (p < 0.05). Treatment with hCG 5 days after AI significantly improved pregnancy rates in those cows that were treated with the H protocol compared with saline treatments (41.5% vs 24.8%; p < 0.01). O and H were more effective in primiparous than in pluriparous cows (46.1% vs 29.9%; p < 0.1 and 43.6% vs 24.6%; p < 0.01). First service pregnancy rates were higher in primiparous hCG-treated than in pluriparous hCG-treated cows (57.9% vs 32.3%; p < 0.01). The pregnancy rate was higher for the hCG-treated cows compared with saline-treated cows during warm period (37.9% vs 23.6%; p < 0.001).