Animal Reproduction最新文献

Assisted reproductive technologies, particularly sex-sorted semen and in vitro embryo production (IVP) can contribute to accelerating genetic gain in both dairy breeds and beef breeds suitable for mating with dairy cows by increasing the number of offspring produced from genetically elite dams. Use of sexed semen has rapidly increased in recent years, accelerating herd genetic gain through selection of the best genetic merit dams to breed replacements, allowing non-replacement dams to be bred to beef sires or to act as recipients of beef embryos to improve calf marketability. IVP offers significant advantages over traditional multiple ovulation embryo transfer (MOET) including increased flexibility in sire usage allowing multiple pregnancies from elite dam-sire combinations to be generated, the ability to produce more embryos per unit time per genetically elite female, the ability to use oocytes from prepubertal females and the more efficient use of rare or high-cost semen straws. Despite these benefits, significant challenges relating to pregnancy loss after embryo transfer, particularly after cryopreservation of IVP embryos, and issues relating to peri- and postnatal health and development of IVP offspring remain to be resolved and hamper the more widespread application of the technology. Improving our understanding of the underlying physiological and molecular mechanisms that regulate early embryo development, embryo-endometrial interactions and lead to successful pregnancy establishment is necessary to understand and elucidate the causes of pregnancy loss and provide a basis for new strategies to improve pregnancy outcomes and reproductive efficiency.

Reproductive tract inflammatory diseases (RTID) present significant health challenges in domestic animals, impacting welfare, fertility, and productivity. Traditionally, antibiotics have been the primary treatment for these conditions, however, the rise of antimicrobial resistance calls for alternative approaches. The microbiome of the female reproductive tract plays a vital role in maintaining reproductive health, and emerging evidence suggests that microbiome-based therapies, such as 'natural' or 'synthetic' microbiome transplantation, may offer sustainable solutions for RTID management. This review explores the composition and dynamics of the reproductive microbiome in both healthy and diseased states in cows, mares, sows, dogs, and cats. It also examines current treatments and the potential for microbiome-based interventions to replace or complement antibiotic therapies. Although research on microbiome-based therapies for preventing or treating RTID in domestic animals is virtually non-existent, vaginal and uterine microbiomes transplantation in mice and women show promise but require further investigation to evaluate their efficacy and safety across species with varying reproductive physiologies. Additionally, synthetic microbiome therapies present a controlled and reproducible alternative, though they face challenges in design, engraftment, and regulatory approval. The transition from antibiotic dependence to microbiome-based solutions marks a paradigm shift in veterinary medicine, but successful implementation demands a deeper understanding of host-microbiome interactions, rigorous safety protocols, and species-specific research.

Unlocking the developmental potential of oocytes at various stages of folliculogenesis represents a major challenge in reproductive biology and assisted reproductive technologies. While in vitro maturation (IVM) of fully grown oocytes is widely applied, the vast majority of oocytes enclosed within early-stage follicles remain underutilized. This review outlines current advancements in in vitro culture systems designed to support oocyte growth and differentiation, with particular attention to the contributions of the authors. Key developments, mainly encompassing the bovine species, include the use of prematuration strategies to enhance the competence of oocytes retrieved from antral follicles, stepwise in vitro culture protocols for growing oocytes from early antral follicles, and efforts to establish defined systems for preantral follicle culture. Emerging insights into chromatin dynamics, cumulus-oocyte communication, and epigenetic regulation are shaping the design of tailored culture environments. Despite promising progress, significant challenges remain in replicating the complexity of in vivo folliculogenesis, particularly in non-rodent models. Addressing these challenges will be critical to expanding the oocyte pool available for reproductive and biotechnological applications, with broad implications for fertility preservation, livestock breeding, and fundamental research.

In vitro embryo production (IVEP) has become a cornerstone of genetic advancement in cattle, yet its efficiency remains suboptimal and highly variable. This review synthesizes current knowledge on donor selection and management strategies aimed at optimizing IVEP outcomes. Central to IVEP success is the quantity and developmental competence of oocytes, which is influenced by both intrinsic donor characteristics and extrinsic management interventions. Ovarian superstimulation using follicle-stimulating hormone (FSH) has emerged as a key strategy to enhance oocyte yield and quality, with evidence supporting dose-dependent improvements in embryo development and yield. Protocol refinements-including timing, duration, and delivery mode of FSH- can further influence IVEP efficacy. Donor-specific factors such as age, pregnancy status, and size of the ovarian reserve, assessed via antral follicle count (AFC) or anti-Müllerian hormone (AMH) concentrations, significantly affect oocyte competence and/or embryo yield. Additionally, newly developed genomic traits and selection indexes, offer predictive value for donor performance and enable integration of IVEP-specific traits into breeding programs. High AMH donors consistently outperform low AMH counterparts, and emerging evidence suggests that tailoring superstimulation protocols to AMH phenotype can further enhance IVEP outcomes. The integration of physiological and genomic data provides the opportunity for developing targeted, phenotype/genotype-driven superstimulation protocols to maximize IVEP efficiency in a cost-effective and biologically sound manner.

The increase in free fatty acid (FFA) levels in the circulation and follicular fluid in response to the negative energy balance of dairy cows has received significant attention during the last decades. However, until recently the potential effect of FFA on the periovulatory steroid environment has been overlooked. The well-orchestrated luteinizing hormone (LH) peak induces a steroid shift in the periovulatory follicle, from Estradiol-17β (E2) dominance around the LH peak towards progesterone (P4) dominance around ovulation, and is a prerequisite for optimal cytoplasmic and nuclear maturation in the oocyte and oocyte developmental competence. Recent insights in literature demonstrate a link between saturated and mono-unsaturated FFAs and the expression of gonadotrophin receptors, follicle stimulating hormone (FSH)R and LHR, including steroid related enzymes and E2 synthesis by in vitro granulosa cells. The current review will focus on the potential role of mono-unsaturated oleic acid, the most abundant FFA in follicular fluid, on steroidogenesis and its potential effect on the cumulus-oocyte-complex (COC) during final maturation. The data of this review suggest the potential for a regulatory interlinked system, which includes the oocyte secreted factor FGF10 and oleic acid, that modulates the steroidogenic switch from E2 to P4 in the periovulatory follicle, via actions that involve the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway in support of the delicate and well-orchestrated dialogue between the oocyte and cumulus cells during final maturation of COCs.

The acquisition of oocyte competence in cattle, encompassing both cytoplasmic and nuclear maturation, is essential for successful fertilization and embryonic development. This competence is progressively achieved during the latter stages of the oocyte growth phase and completed within the dominant follicle (DF). The unique hormonal and immunological environment of the DF during oestrous supports oocyte "capacitation," a process involving organelle reorganization, mRNA storage and meiosis resumption, which fully prepares the oocyte for fertilization. These changes differentiate oocytes from the DF from those of subordinate follicles, explaining why only oocytes from the DF mature and ovulate successfully. Despite advances in assisted reproductive technologies like in vitro maturation (IVM) and in vitro fertilization (IVF), developmental outcomes remain inferior compared to in vivo matured oocytes, largely due to incomplete or altered oocyte maturation in vitro. Blastocyst rates after IVM/IVF are substantially lower (~35%) than those from in vivo matured oocytes (58-78%). The heterogeneity of oocytes retrieved from antral follicles and the lack of exposure to the natural follicular environment during IVM are key factors limiting developmental competence. Here we describe the molecular changes in bovine oocytes from DFs, collected at 24 and 2 h before ovulation without ovarian stimulation, using single-cell RNA sequencing and bisulfite sequencing to assess gene expression and DNA methylation dynamics. Results revealed significant shifts in transcripts related to oxidative phosphorylation, highlighting the crucial role of energy metabolism during oocyte capacitation. DNA methylation changes were subtle but indicated a more dynamic and less stable epigenome in fully-grown oocytes than previously assumed. Overall, understanding the gene expression and epigenetic landscape during oocyte maturation in the DF offers valuable insights into improving oocyte quality and ART outcomes in cattle. Optimizing the maturation environment to better mimic natural follicular conditions could enhance reproductive efficiency in bovine production systems.

This review provides an up-to-date overview of the roles of the oviduct during the periconception period and underlying mechanisms. The functions of the oviduct before, during, and after fertilization are highlighted, with special focus on the effects of epithelial cell contact and luminal secretions on sperm selection mechanisms and acquisition of fertilization ability. The current knowledge on how the oviduct contributes to support fertilization and embryo development via the overall physical milieu (oxygen tension, fluid current, ciliated epithelial cells) and the role of its secretions is also provided. Altogether, the review underlines the unique role of the oviduct during gamete selection and early embryo development, which so far has not been completely possible to mirror when assisted reproductive technologies (ART) are used. Unveiling the most important functional components of oviductal secretions that contribute to better sperm selection, and boost sperm fertilizing ability and early embryo development, can indeed be useful to improve the outcomes of current in vitro systems used in ART.

Embryo development is a complex process that requires several physiological and molecular events to happen harmoniously, and all of this begins with the interaction of the oocyte and sperm. The ability of an oocyte to become a healthy blastocyst is the result of several critical events that are determinants for the successful development of the embryo. Among these events are the sperm's ability to interact with and penetrate the oocyte, carry out syngamy, the developmental competence of the oocyte to support mitotic divisions, and the proper activation of the molecular machinery to regulate the embryo's developmental competence during the early stages of embryonic development. Some of these events originate from either the paternal or maternal side. The focus of this review is to explore the contributions of the paternal side to reproduction in general, with greater emphasis on early embryo development. A deeper understanding of these paternal factors and their influence on embryo development and overall fertility will support the development of new strategies for selecting sires to improve reproductive efficiency in cattle.

Understanding the molecular mechanisms regulating the development of bovine pre-implantation embryos and formation of embryo-like structures (blastoids) is essential to uncover the causes of infertility and develop promising novel assisted reproductive technologies (ARTs). This review presents an updated view of functional genome characterization of bovine pre-implantation development. The use of genomic phenotyping and candidate gene perturbation approaches to uncover molecular factors governing bovine early embryonic development are discussed. This review also delves into the latest breakthroughs in the development of bovine blastoids and highlights key molecular signaling for the creation of bovine blastoids.

The productivity in livestock systems is related to the reproductive efficiency of herds. Over the years, strategies have been developed to improve the reproductive rates of female cattle. Initially, estrus synchronization protocols were developed, however, difficulties related to prolonged postpartum anestrus and estrus observation resulted in low conception rates in these programs. Subsequently, hormonal associations were used to synchronize ovulation and inseminate female cattle at a predetermined time, eliminating the need for estrus observation and improving the fertility rates of cows in postpartum anestrus. Several adjustments were made to improve the response to a timed-artificial insemination (TAI) protocol in different production systems and animal categories. Finally, the development of recombinant drugs and nanotechnology may optimize production systems. Thus, the objective of this review is to detail the research carried out over the years related to the evolution of TAI protocols.