The fibroblast growth factor 2 gene is associated with embryonic mortality in cattle

Strong associations between the FGF-2 gene and productivity traits of Holstein-Friesian dairy cattle

Sustainability in dairy cattle farms depends on the efficiency of milk yield and reproductive traits. Thus, this study aimed to investigate the effect of the FGF-2/Csp6I gene and major environmental factors on these traits in Holstein-Friesian cattle. A total of 212 whole blood samples were collected from the Vena coccygea of cattle and the data obtained from these samples were used in all statistical analyses. Then, the restriction fragment length polymorphism (RFLP) method (determination of genotypes) was conducted and programs including PopGene (allele and genotype frequencies), Minitab (association analyses) and MTDFREML (variance components and genetic parameters) were used. Alleles A (0.4269) and G (0.5731) as well as genotypes AA (0.174), AG (0.505) and GG (0.321) were found, indicating that the population is polymorphic and in Hardy-Weinberg equilibrium (P > 0.05). The effect of the Csp6I polymorphism of FGF-2 gene on peak milk yield (PMY) (P < 0.01); lactation milk yield (LMY), milking time (MT), 305-day and 200-day lactation milk yield (LMY305 and LMY200), average daily milk yield (ADMY) (P < 0.05); 100-day lactation milk yield (LMY100), age of using in first breeding (AUFB) and number of inseminations per conception (NIPC) (P < 0.10) were significant. The heritability of milk yield traits and the correlation between direct and maternal heritability for reproductive traits were high. Furthermore, the breeding value of PMY was higher for the AA genotype (0.745 ± 0.292) than for the AG genotype (-0.268 ± 0.171) (P < 0.05). As a result, the A allele and AA genotype for the FGF-2/Csp6I gene had an increasing effect on milk yield without compromising reproductive performance in Holstein-Friesian dairy cattle.

Influences of sire conception rate on pregnancy establishment in dairy cattle

Establishment of pregnancy in cattle is complex and encompasses ovulation, fertilization, blastocyst formation and growth into an elongated conceptus, pregnancy recognition signaling, and development of the embryo and placenta. The objective here was to investigate sire influences on pregnancy establishment in cattle. First, 10 Holstein bulls were classified as high or low fertility based on their sire conception rate (SCR) value. In a field trial, pregnancy at first timed insemination was not different between high and low SCR bulls. Next, 5 of the 10 sires were phenotyped using in vitro and in vivo embryo production. There was no effect of SCR classification on in vitro embryo cleavage rate, but low SCR sires produced fewer day 8 blastocysts. In superovulated heifers, high SCR bulls produced a lower percentage of unfertilized oocytes and fewer degenerated embryos compared to low SCR bulls. Recipient heifers received three to five in vivo produced embryos from either high or low SCR sires on day 7 postestrus. Day 16 conceptus recovery and length were not different between SCR groups, and the conceptus transcriptome was not appreciably different between high and low SCR sires. The reduced ability of embryos from low SCR bulls to establish pregnancy is multifactorial and encompasses sperm fertilizing ability, preimplantation embryonic development, and development of the embryo and placenta after conceptus elongation and pregnancy recognition. These studies highlight the importance of understanding genetic contributions of the sire to pregnancy establishment that is crucial to increase reproductive efficiency in dairy cattle.

Characteristics of candidate genes associated with embryonic development in the cow: Evidence for a role for WBP1 in development to the blastocyst stage

The goal was to gain understanding of how 12 genes containing SNP previously related to embryo competence to become a blastocyst (BRINP3, C1QB, HSPA1L, IRF9, MON1B, PARM1, PCCB, PMM2, SLC18A2, TBC1D24, TTLL3 and WBP1) participate in embryonic development. Gene expression was evaluated in matured oocytes and embryos. BRINP3 and C1QB were not detected at any stage. For most other genes, transcript abundance declined as the embryo developed to the blastocyst stage. Exceptions were for PARM1 and WBP1, where steady-state mRNA increased at the 9-16 cell stage. The SNP in WBP1 caused large differences in the predicted three-dimensional structure of the protein while the SNP in PARM1 caused smaller changes. The mutation in WBP1 causes an amino acid substitution located close to a P-P-X-Y motif involved in protein-protein interactions. Moreover, the observation that the reference allele varies between mammalian species indicates that the locus has not been conserved during mammalian evolution. Knockdown of mRNA for WBP1 decreased the percent of putative zygotes becoming blastocysts and reduced the number of trophectoderm cells and immunoreactive CDX2 in the resulting blastocysts. WBP1 is an important gene for embryonic development in the cow. Further research to identify how the SNP in WBP1 affects processes leading to differentiation of the embryo into TE and ICM lineages is warranted.

Luteal angiogenesis and its control

Angiogenesis, the formation of new blood vessels from preexisting ones, is critical to luteal structure and function. In addition, it is a complex and tightly regulated process. Not only does rapid and extensive angiogenesis occur to provide the corpus luteum with an unusually high blood flow and support its high metabolic rate, but in the absence of pregnancy, the luteal vasculature must rapidly regress to enable the next cycle of ovarian activity. This review describes a number of key endogenous stimulatory and inhibitory factors, which act in a delicate balance to regulate luteal angiogenesis and ultimately luteal function. In vitro luteal angiogenesis cultures have demonstrated critical roles for fibroblast growth factor 2 (FGF2) in endothelial cell proliferation and sprouting, although other factors such as vascular endothelial growth factor A (VEGFA) and platelet-derived growth factor were important modulators in the control of luteal angiogenesis. Post-transcriptional regulation by small non-coding microRNAs is also likely to play a central role in the regulation of luteal angiogenesis. Appropriate luteal angiogenesis requires the coordinated activity of numerous factors expressed by several cell types at different times, and this review will also describe the role of perivascular pericytes and the importance of vascular maturation and stability. It is hoped that a better understanding of the critical processes underlying the transition from follicle to corpus luteum and subsequent luteal development will benefit the management of luteal function in the future.

An application of MeSH enrichment analysis in livestock

An integral part of functional genomics studies is to assess the enrichment of specific biological terms in lists of genes found to be playing an important role in biological phenomena. Contrasting the observed frequency of annotated terms with those of the background is at the core of overrepresentation analysis (ORA). Gene Ontology (GO) is a means to consistently classify and annotate gene products and has become a mainstay in ORA. Alternatively, Medical Subject Headings (MeSH) offers a comprehensive life science vocabulary including additional categories that are not covered by GO. Although MeSH is applied predominantly in human and model organism research, its full potential in livestock genetics is yet to be explored. In this study, MeSH ORA was evaluated to discern biological properties of identified genes and contrast them with the results obtained from GO enrichment analysis. Three published datasets were employed for this purpose, representing a gene expression study in dairy cattle, the use of SNPs for genome‐wide prediction in swine and the identification of genomic regions targeted by selection in horses. We found that several overrepresented MeSH annotations linked to these gene sets share similar concepts with those of GO terms. Moreover, MeSH yielded unique annotations, which are not directly provided by GO terms, suggesting that MeSH has the potential to refine and enrich the representation of biological knowledge. We demonstrated that MeSH can be regarded as another choice of annotation to draw biological inferences from genes identified via experimental analyses. When used in combination with GO terms, our results indicate that MeSH can enhance our functional interpretations for specific biological conditions or the genetic basis of complex traits in livestock species.

Reproductive technologies and genomic selection in dairy cattle

Genomic tools are now available for most livestock species and are used routinely for genomic selection (GS) in cattle. One of the most important developments resulting from the introduction of genomic testing for dairy cattle is the application of reasonably priced low-density single nucleotide polymorphism technology in the selection of females. In this context, combining genome testing and reproductive biotechnologies in young heifers enables new strategies to generate replacement and elite females in a given period of time. Moreover, multiple markers have been detected in biopsies of preimplantation stage embryos, thus paving the way to develop new strategies based on preimplantation diagnosis and the genetic screening of embryos. Based on recent advances in GS, the present review focuses on new possibilities inherent in reproductive technologies used for commercial purposes and in genetic schemes, possible side effects and beneficial impacts on reproductive efficiency. A particular focus is on the different steps allowing embryo genotyping, including embryo micromanipulation, DNA production and quality assessment.

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.

Discovery of single nucleotide polymorphisms in candidate genes associated with fertility and production traits in Holstein cattle

Background

Identification of single nucleotide polymorphisms (SNPs) for specific genes involved in reproduction might improve reliability of genomic estimates for these low-heritability traits. Semen from 550 Holstein bulls of high (≥ 1.7; n = 288) or low (≤ −2; n = 262) daughter pregnancy rate (DPR) was genotyped for 434 candidate SNPs using the Sequenom MassARRAY® system. Three types of SNPs were evaluated: SNPs previously reported to be associated with reproductive traits or physically close to genetic markers for reproduction, SNPs in genes that are well known to be involved in reproductive processes, and SNPs in genes that are differentially expressed between physiological conditions in a variety of tissues associated in reproductive function. Eleven reproduction and production traits were analyzed.

Results

A total of 40 SNPs were associated (P < 0.05) with DPR. Among these were genes involved in the endocrine system, cell signaling, immune function and inhibition of apoptosis. A total of 10 genes were regulated by estradiol. In addition, 22 SNPs were associated with heifer conception rate, 33 with cow conception rate, 36 with productive life, 34 with net merit, 23 with milk yield, 19 with fat yield, 13 with fat percent, 19 with protein yield, 22 with protein percent, and 13 with somatic cell score. The allele substitution effect for SNPs associated with heifer conception rate, cow conception rate, productive life and net merit were in the same direction as for DPR. Allele substitution effects for several SNPs associated with production traits were in the opposite direction as DPR. Nonetheless, there were 29 SNPs associated with DPR that were not negatively associated with production traits.

Conclusion

SNPs in a total of 40 genes associated with DPR were identified as well as SNPs for other traits. It might be feasible to include these SNPs into genomic tests of reproduction and other traits. The genes associated with DPR are likely to be important for understanding the physiology of reproduction. Given the large number of SNPs associated with DPR that were not negatively associated with production traits, it should be possible to select for DPR without compromising production.

Genes of the transforming growth factor-beta signalling pathway are associated with pre-implantation embryonic development in cattle

One of the main factors affecting cattle fertility is pre-implantation development of the bovine embryo, which is a complex process regulated by various signal-transduction pathways. The transforming growth factor-β (TGF-β) signalling system, which is responsible for many biological processes including cell proliferation, differentiation and apoptosis, also is involved in embryo development. We hypothesized that altered expression of TGF-β genes in pre-implantation bovine embryos is associated with morphological abnormalities of these embryos. To test this hypothesis, we produced embryos in vitro and classified them at the blastocyst stage as either normally developed blastocysts or degenerates (growth-arrested embryos). The expression patterns of 25 genes from the TGF-β pathway were assessed using quantitative real time PCR. Ten genes showed differential expression between the two embryo groups, four genes displayed similar expressional profiles, and 11 genes had no detectable expression. An altered expression profile was statistically significant for 10 of the 14 expressed genes, and all were up-regulated in degenerate embryos vs. blastocysts. Furthermore, genomic association analysis of the cows from which embryos were produced revealed a significant association of ID3 and BMP4 polymorphisms--two of the most significant differentially expressed genes--with fertilization rate and blastocyst rate, respectively. Taken together, we conclude that TGF-β pathway genes, especially BMP4 and ID3 play a vital function in the regulation of pre-implantation embryo development at both embryo and maternal levels. Hence, these genes may be suitable as genetic markers for embryo development and fertility in cattle.

Differential expression of heat shock protein genes and their splice variants in bovine preimplantation embryos

Heat shock proteins (HSP) are among the first proteins produced during embryonic development and are crucial to cell function; their activities include folding, unfolding, transport, and localization of proteins and differentiation and regulation of the embryonic cell cycle. Although HSP have been extensively studied in humans and mice, limited information exists on the roles of these genes in bovine embryos. As such, the objectives of this study were to profile the expression of HSP and their splice variants in bovine embryos (degenerates vs. blastocysts) and to carry out association analysis with fertility traits. Quantitative real time PCR analysis revealed differences in expression that ranged from 1.5- to 7.6-fold in degenerate embryos compared with blastocysts. Interestingly, all members of the HSP40 family were found to be upregulated in degenerate embryos. Analysis of current bovine Ensembl data showed that 13 HSP genes have 1 transcript each, 2 genes have 2 transcripts each, and 2 have 3 transcripts each. Some splice variants show differential expression between degenerate embryos and blastocysts, whereas others were not expressed at all in embryos, which implies different functions of these transcripts in embryonic development. The most significant differentially expressed genes were further investigated for association with fertility and development traits. Single nucleotide polymorphisms in DNAJC15 and DNAJC27 were found to be associated with blastocyst rate and fertilization rate, respectively. Collectively, the roles of HSP in fertilization and early development of cattle embryos are important.

Short communication: expression and alternative splicing of POU1F1 pathway genes in preimplantation bovine embryos

Early embryo loss is a major contributing factor to cow infertility and that 70 to 80% of this loss occurs between d 8 and 16 postfertilization. However, little is known about the molecular mechanisms and the nature of genes involved in normal and abnormal embryonic development. Moreover, information is limited on the contributions of the genomes of dams and of embryos to the development and survival of preimplantation embryos. We hypothesized that proper gene expression level in the developing embryo is essential for embryo survival and pregnancy success. As such, the characterization of expression profiles in early embryos could lead to a better understanding of the mechanisms involved in normal and abnormal embryo development. To test this hypothesis, 2 d-8 embryo populations (degenerate embryos and blastocysts) that differed in morphology and developmental status were investigated. Expression levels of POU1F1 pathway genes were estimated in 4 sets of biological replicate pools of degenerate embryos and blastocysts. The OPN and STAT5A genes were found to be upregulated in degenerate embryos compared with blastocysts, whereas STAT5B showed similar expression levels in both embryo groups. Analysis of splice variants of OPN and STAT5A revealed expression patterns different from the total expression values of these genes. As such, measuring expression of individual transcripts should be considered in gene expression studies.

Association of milk protein genes with fertilization rate and early embryonic development in Holstein dairy cattle

Concomitant with intensive selection for increased milk yield, reproductive performance of dairy cows has declined in the last decades, in part due to an unfavourable genetic relationship between these traits. Given that the six main milk protein genes (i.e. whey proteins and caseins) are directly involved in milk production and hence have been a target of the strong selection aimed at improving milk yield in dairy cattle, we hypothesized that these genes could show selection footprints associated with fertility traits. In this study, we used an in-vitro fertilization (IVF) system to test genetic association between 66 single nucleotide polymorphisms (SNPs) in the four caseins (αS1-casein, αS2-casein, β-casein and κ-casein) and the two whey protein genes (α-lactalbumin and β-lactoglobulin) with fertilization rate and early embryonic development in the Holstein breed. A total of 6893 in-vitro fertilizations were performed and a total of 4661 IVF embryos were produced using oocytes from 399 ovaries and semen samples from 12 bulls. Associations between SNPs and fertility traits were analysed using a mixed linear model with genotype as fixed effect and ovary and bull as random effects. A multiple testing correction approach was used to account for the correlation between SNPs due to linkage disequilibrium. After correction, polymorphisms in the LALBA and LGB genes showed significant associations with fertilization success and blastocyst rate. No significant associations were detected between SNPs located in the casein region and IVF fertility traits. Although the molecular mechanisms underlying the association between whey protein genes and fertility have not yet been characterized, this study provides the first evidence of association between these genes and fertility traits. Furthermore, these results could shed light on the antagonistic relationship that exists between milk yield and fertility in dairy cattle.

Effect of polymorphisms at the STAT5A and FGF2 gene loci on reproduction, milk yield and lameness of Holstein cows

The objective of this study was to investigate the association of polymorphisms at the STAT5A and FGF2 gene loci with fertility, lactation milk yield and lameness in dairy cattle. Five hundred and eighteen primiparous Holstein cows were included in the study. Several reproductive traits were considered including conception rate (0/1) at first insemination, conception rate (0/1) in a 305-day lactation, number of inseminations per conception, interval (days) from calving to conception for cows that conceived in the first 305 days of lactation and age at first calving. Milk yield and lameness incidence were also recorded. Genotyping was performed using PCR-RFLP. The effect of allele substitution at each gene locus on reproductive traits, milk yield and lameness was assessed with single-trait mixed linear models. No significant associations were found between reproduction traits and any of the studied polymorphisms, apart from age at first calving, for which STAT5A polymorphism had a suggestive effect (P = 0.077). In addition, no significant effect of any polymorphism on lameness was found. Replacement of the C by G allele at the STAT5A locus was associated with a significant (P<0.05) increase in lactation milk yield, suggesting that this locus could be considered in gene assisted selection for the genetic improvement of milk production.

Effects of gamete source and culture conditions on the competence of in vitro-produced embryos for post-transfer survival in cattle

One limitation to the use of in vitro-produced embryos in cattle production systems is the fact that pregnancy rates after transfer to recipients are typically lower than when embryos produced in vivo are transferred. Conceptually, the oocyte and spermatozoon from which the embryo is derived could affect competence for post-transfer survival. There are sire differences in embryonic survival after transfer, but there is little evidence that an embryo's ability to establish pregnancy is determined by sex sorting of spermatozoa by flow cytometry. The role of the source of the oocyte as a determinant of embryonic survival after transfer has not been examined carefully. Conditions for embryo culture after fertilisation can have an impact on the ability of the embryo to establish pregnancy following transfer. Among the specific molecules produced in the reproductive tract of the cow that have been shown to improve competence of in vitro-produced embryos for post-transfer survival are colony-stimulating factor 2, insulin-like growth factor-1 (for recipients exposed to heat stress) and hyaluronan (for less-advanced embryos). There is also a report that embryo competence for post-transfer survival can be improved by inclusion of a carbon-activated air filtration system in the incubator used to culture embryos. Progress in developing culture systems to improve embryonic competence for survival after transfer would be hastened by the development of in vitro assays that accurately predict the potential of an embryo to establish pregnancy after transfer. A group of 52 genes has been identified that are differentially expressed in embryos that developed to term v. embryos that did not establish pregnancy. Perhaps a gene microarray consisting of these genes, alone or in combination with other genes, could be used to screen embryos for competence to establish pregnancy.

Effects of signal transducer and activator of transcription (STAT) genes STAT1 and STAT3 genotypic combinations on fertilization and embryonic survival rates in Holstein cattle

Infertility is a major cause of dairy cow culling and economic loss. Signal transducer and activator of transcription (STAT) proteins are transcription factors that play an important role in fertility and early embryonic development, among many other functions. Previous studies have reported the association of several genes from the JAK/STAT signaling pathway with fertility traits in cattle. The STAT1 and STAT3 genes are members of this pathway and are known to interact with each other by forming a heterodimer complex that enters the nucleus and controls expression of specific genes. Thus, the objective of this study was to investigate the effects of the interactions between polymorphisms in these genes on fertilization and early embryonic survival rates using an in vitro fertilization system. A total of 7,519 oocytes, collected from 445 ovaries, were exposed to sperm and a total of 5,075 embryos were produced. Fertilization rate was calculated as the number of cleaved embryos at 48 h post-fertilization out of the total number of oocytes exposed to sperm. Early embryonic survival rate of embryos was calculated as the number of blastocysts on d 7 of development out of the total number of embryos cultured. Effects of ovary genotypes on fertilization and early embryonic survival rates were evaluated. Single-SNP analysis revealed a statistically significant association between SNP25402 in STAT3 and fertilization rate. Oocytes produced from ovaries with AA genotype showed a 0.701 fertilization rate versus 0.666 and 0.663 for oocytes produced from AC and CC ovaries, respectively. The interaction between STAT3 SNP (SNP19069/SNP25402) was highly significant for survival rate but not for fertilization rate. Also, the interaction between STAT1 SNP and SNP19069 was highly significant for survival rate. Genotype combinations found to promote fertilization and embryonic survival could be incorporated into breeding programs aimed at improving fertility performance in dairy cattle.

Transcriptomic profiling of bovine IVF embryos revealed candidate genes and pathways involved in early embryonic development

Background

Early embryonic loss is a large contributor to infertility in cattle. Although genetic factors are known to affect early embryonic development, the discovery of such factors has been a serious challenge. The objective of this study was to identify genes differentially expressed between blastocysts and degenerative embryos at early stages of development.

Results

Using microarrays, genome-wide RNA expression was profiled and compared for in vitro fertilization (IVF) - derived blastocysts and embryos undergoing degenerative development up to the same time point. Surprisingly similar transcriptomic profiles were found in degenerative embryos and blastocysts. Nonetheless, we identified 67 transcripts that significantly differed between these two groups of embryos at a 15% false discovery rate, including 33 transcripts showing at least a two-fold difference. Several signaling and metabolic pathways were found to be associated with the developmental status of embryos, among which were previously known important steroid biosynthesis and cell communication pathways in early embryonic development.

Conclusions

This study presents the first direct and comprehensive comparison of transcriptomes between IVF blastocysts and degenerative embryos, providing important information for potential genes and pathways associated with early embryonic development.

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.

Analysis of segregation distortion and association of the bovine FGF2 with fertilization rate and early embryonic survival

Fibroblast growth factor 2 (FGF2) plays an important role in fertility and early embryo development. The objectives of this study were to test the association of FGF2 polymorphisms with fertilization success in cattle using an in vitro fertilization experimental system and to investigate the mechanisms leading to the presence of rare alleles of FGF2 in the Holstein population. A total of 7502 fertilizations were performed and a total of 5049 embryos were produced to collect fertilization and embryo survival records. A total of 444 ovaries, from which oocytes were aspirated and fertilized, were genotyped for two single nucleotide polymorphisms (SNPs) previously identified in FGF2 (g.23G>T and g.11646A>G). Frequency of the TT genotype of the g.23G>T SNP was low in the ovary population (5.4%) and in a different Holstein cattle population (6.6%) examined in this study. Single SNP analysis showed that both SNPs were associated with early embryonic survival rate. Two-way interaction analysis revealed significant association of epistatic interaction between the SNPs with fertilization rate. To test whether or not low frequency of allele T for the g.23G>T SNP in the population is a result of a fertilization failure of T oocytes, semen from six GG bulls was used to fertilize a total of 458 oocytes obtained from 19 GT ovaries. A significant segregation distortion was observed for 169 embryos genotyped for the g.23G>T SNP. We conclude that oocytes carrying the T allele show a reduced fertilization rate and that segregation distortion leads to rarity of the TT genotype in the population.

Monoallelic maternal expression of STAT5A affects embryonic survival in cattle

Background

Reproductive disorders and infertility are surprisingly common in the human population as well as in other species. The decrease in fertility is a major cause of cow culling and economic loss in the dairy herd. The conception rate has been declining for the past 30–50 years. Conception rate is the product of fertilization and embryonic survival rates. In a previous study, we have identified associations of several single nucleotide polymorphisms (SNPs) in the signal transducer and activator 5A (STAT5A) with fertilization and survival rates in an in vitro experimental system. The objectives of this study are to fine map the STAT5A region in a search for causative mutations and to investigate the parent of origin expression of this gene.

Results

We have performed a total of 5,222 fertilizations and produced a total of 3,696 in vitro fertilized embryos using gametes from 440 cows and eight bulls. A total of 37 SNPs were developed in a 63.4-kb region of genomic sequence that includes STAT5A, STAT3, and upstream and downstream sequences of these genes. SNP153137 (G/C) in exon 8 of STAT5A was associated with a significant variability in embryonic survival and fertilization rate compared to all other examined SNPs. Expression analysis revealed that STAT5A is primarily monoallelically expressed in early embryonic stages but biallelically expressed in later fetal stages. Furthermore, the occurrence of monoallelic maternal expression of STAT5A was significantly higher in blastocysts, while paternal expression was more frequent in degenerative embryos.

Conclusion

Our results imply that STAT5A affects embryonic survival in a manner influenced by developmental stage and allele parent of origin.

Consequences for the bovine embryo of being derived from a spermatozoon subjected to post-ejaculatory aging and heat shock: development to the blastocyst stage and sex ratio

The objective was to determine whether aging of sperm caused by incubation at normothermic (38.5 C) or heat shock (40 C) temperatures for 4 h prior to oocyte insemination affects sperm motility, fertilizing ability, competence of the resultant embryo to develop to the blastocyst stage and blastocyst sex ratio. In the first experiment, the percent of sperm that were motile was reduced by aging (P<0.001) and the reduction in motility was greater for sperm at 40 C compared to sperm at 38.5 C (P<0.01). In the second experiment, oocytes were inseminated with aged sperm. A smaller percent of oocytes fertilized with sperm aged at either temperature cleaved by Day 3 after insemination than oocytes fertilized with fresh sperm (P<0.05). There was no effect of sperm aging on the percent of oocytes or cleaved embryos that developed to the blastocyst stage. Aging of sperm before fertilization at 38.5 C reduced the percent of blastocysts that were male (P=0.08). In the third experiment, incubation of sperm at 38.5 C or 40 C for 4 h did not reduce fertilizing ability of sperm as determined by pronuclear formation at 18 h post insemination. In conclusion, aging of sperm reduced cleavage rate and the percent of blastocysts that were males but had no effect on the developmental capacity of the embryo. The effect of aging on cleavage rate may represent reduced motility and errors occurring after fertilization and pronuclear formation. Aging at a temperature characteristic of maternal hyperthermia had little additional effect except that polyspermy was reduced. Results indicate that embryo competence for development to the blastocyst stage is independent of sperm damage as a result of aging for 4 h at normothermic or hyperthermic temperatures.