To be or not to be—Determinants of embryonic survival following heat shock

Heat Stress: A Serious Disruptor of the Reproductive Physiology of Dairy Cows

Global warming is a significant threat to the sustainability and profitability of the dairy sector, not only in tropical or subtropical regions but also in temperate zones where extreme summer temperatures have become a new and challenging reality. Prolonged exposure of dairy cows to high temperatures compromises animal welfare, increases morbidity, and suppresses fertility, resulting in devastating economic losses for farmers. To counteract the deleterious effects of heat stress, cattl e employ various adaptive thermoregulatory mechanisms including molecular, endocrine, physiological, and behavioral responses. These adaptations involve the immediate secretion of heat shock proteins and cortisol, followed by a complex network of disrupted secretion of metabolic and reproductive hormones such as prolactin, ghrelin, ovarian steroid, and pituitary gonadotrophins. While the strategic heat stress mitigation measures can restore milk production through modifications of the microclimate and nutritional interventions, the summer fertility records remain at low levels compared to those of the thermoneutral periods of the year. This is because sustainment of high fertility is a multifaceted process that requires appropriate energy balance, undisrupted mode of various hormones secretion to sustain the maturation and fertilizing competence of the oocyte, the normal development of the early embryo and unhampered maternal-embryo crosstalk. In this review, we summarize the major molecular and endocrine responses to elevated temperatures in dairy cows, as well as the impacts on maturing oocytes and early embryos, and discuss the consequences that heat stress brings about in dairy cattle fertility.

Baicalin inhibits oxidative injures of mouse uterine tissue induced by acute heat stress through activating the Keap1/Nrf2 signaling pathway

Heat stress effect the physiological functions of body, and reproductive system is one of the most sensitive. It's imperative to find out suitable measures to alleviate harmful effects of heat stress. Baicalin is well-known with its antioxidative property. To examine whether Baicalin could reduce oxidative injures of uterine tissue in heat-stressed mice. The mice were divided into four groups: control (Con), Baicalin (Bai), heat stress (H) and heat stress plus Baicalin (H + Bai). The oxidative damage of uterine tissue was detected by ELISA, H&E staining, tunnel assay and immunohistochemical staining. The protein/mRNA expressions of Keap1/Nrf2 related factors were detected by Western blot or QPCR. The results showed that mice heat-stressed at 41 °C for 2 h induced macroscopic changes, significantly increased MDA content and reduced activities of antioxidant enzymes including SOD, CAT and GSH-Px of the uterine tissue. Compared with Con group, heat stress up-regulated caspase-3 and caspase-9, enhanced the apoptosis of endometrial epithelial and glandular epithelial cells, improved the HO-1 mRNA/protein and NQO1 protein expressions, while down-regulated the mRNA/protein of Keap1. Compared with H group, antioxidant enzyme activities, Nrf2 protein and Nrf2, NQO1 and GCLC mRNA expressions were significantly increased in the H + Bai group. While the uterine epithelial cells apoptosis, MDA contents, caspase-3, caspase-9 and Keap1 protein and HO-1 mRNA expressions were decreased in the H + Bai group of mice compared with that in H group. Briefly, acute heat stress causes oxidative injures and apoptosis of mouse uterine tissue and Baicalin protects uterine tissue from the damages possibly through Keap1/Nrf2 signaling pathway.

Antioxidants Attenuate Heat Shock Induced Premature Senescence of Bovine Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) have many roles that are important for the body's proper functioning. When the MSC pool is damaged, it is often correlated with impaired development or health of the organism. MSC are known for their anti-inflammatory, immunomodulatory and trophic characteristics that play an important role in the physiological homeostasis of many tissues. Heat shock impairs MSC capacity by inducing the generation of reactive oxygen species and mitochondrial dysfunction, which, in turn, send the cells into a state of premature senescence. Here, we pre-exposed MSC to melatonin, resveratrol, or curcumin, which are natural antioxidative compounds, and tested the protective effects of these substances from oxidative stress and aging. Our data showed that pre-exposure of MSC to antioxidants decreased reactive oxygen species while mitochondrial damage remained high. Additionally, although the proliferation of the cells was slow, antioxidants protected the cells from premature senescence, and subsequent cytokine release was prevented. We conclude that while elevated temperatures directly cause mitochondrial damage, senescence is induced by elevated ROS levels. We suggest that heat shock alters cell and tissue homeostasis by several independent mechanisms; however, reducing tissue senescence will reduce damage and provide a pathway to overcome physiological challenges in animals.

The Melatonin Treatment Improves the Ovarian Responses After Superstimulation in Thai-Holstein Crossbreeds Under Heat Stress Conditions

The effect of heat stress with melatonin treatment on the superovulatory responses and embryo characteristics in Thai-Holstein crossbreeds under heat stress conditions was examined. Six non-lactating cows (replication = 4; n = 24) were assigned to one of 2 treatments in double cross-over design. All cows were superstimulated with traditional treatment. Melatonin group (n = 12): cows received intramuscularly injection 18 mg/50 kg. simultaneously with GnRH injection, while those in the control group (n = 12) received none. Bloods samples were taken to determine lipid peroxidation (MDA) and the activity of the antioxidant enzymes (superoxide dismutase; SOD). The experiment was conducted from April to September, which determined severe heat stress (the mean temperature-humidity index above 77). The results revealed that numbers of large follicles and corpora lutea were higher in the melatonin group than in the control group (p < 0.01). Numbers of recovered ova/embryos, fertilized ova, and transferable embryos were higher in the melatonin group (p < 0.01); meanwhile, more degenerated embryos were found in the control group (p < 0.01). Increased activity of the antioxidant enzymes SOD after melatonin administration decreased MDA levels (p < 0.05). In summary, melatonin administration benefited the ovarian response and embryo quality in superstimulated Thai-Holstein crossbreed affected by heat stress.

The Effects of Heat Shock Protein 70 Addition in the Culture Medium on the Development and Quality of In Vitro Produced Heat Shocked Bovine Embryos

The aims of the present study were to examine the effects of HSP70 addition in the in vitro culture medium of day 3 embryos on their developmental competence and quality. Bovine oocytes (n = 1442) were in vitro matured, inseminated and cultured for the first two days according to standardized methods. The presumptive zygotes were randomly allocated in three experimental groups: Control, C (embryos cultured at 39 °C throughout the culture period), group C41 (temperature was raised to 41 °C from the 48th to 72nd h post insemination (p.i.) and then it returned at 39 °C for the remaining culture period), and group H41 (the temperature modification was the same as in C41 and during heat exposure, HSP70 was added in the culture medium). Cleavage and embryo yield were assessed 48 h p.i. and on days 7, 8, 9, respectively and gene expression in day 7 blastocysts was assessed by RT-PCR. Blastocyst yield was the highest in group C39; and higher in group H41 compared to group C41. From the gene expression analyses, altered expression of 11 genes was detected among groups. The analysis of the orchestrated patterns of gene expression differed between groups. The results of this study confirm the devastating effects of heat stress on embryo development and provide evidence that HSP70 addition at the critical stages can partly counterbalance, without neutralizing, the negative effects of the heat insult on embryos, acting mainly through mechanisms related to energy deployment.

Relationship of the Temperature-Humidity Index (THI) with Ovarian Responses and Embryo Production in Superovulated Thai-Holstein Crossbreds under Tropical Climate Conditions

Heat stress strongly negatively affects reproductive traits in dairy cattle. The purpose of the present study was to investigate the effect of heat stress in superstimulated Thai-Holstein crossbreds under tropical climate conditions. Data included 75 records from 12 superovulated Thai-Holstein crossbreds between 2018 and 2020. Cows were superstimulated with conventional treatment. The mean temperature-humidity index (THI) was evaluated for three data collection periods: during the 9, 21 and 42-day periods before the insemination day to determine the period in which THI mostly affected superstimulation responses. The THI levels/thresholds were determined and interpreted together with the superovulatory response. A significantly negative correlation was obtained for the THI during the period 9 days before insemination. Negative effects on the number of large follicles and corpora lutea began at a THI of 72 and were apparently severe after a THI of 77, similar to the ovulation rate, fertilized ova and transferable embryos (p < 0.05). Meanwhile, more degenerated embryos were found with THI values (p < 0.05). The superovulatory response in Thai-Holstein crossbreds under tropical climate conditions is highly affected by heat stress starting at a THI of 72 and becomes more severe at a THI higher than 77.

Occurrence and greater intensity of estrus in recipient lactating dairy cows improve pregnancy per embryo transfer

The aim of this study was to determine the association between occurrence and intensity of estrous expression with pregnancy success in recipient lactating dairy cows subjected to embryo transfer (ET). Two observational studies were conducted. Holstein cows were synchronized using the same timed ET protocol, based on estradiol and progesterone in both experiments. At 9 d after the end of the timed ET protocol only animals that had ovulated were implanted with a 7-d embryo [experiment 1 (Exp. 1); n = 1,401 ET events from 1,045 cows, and experiment 2 (Exp. 2); n = 1,147 ET events from 657 cows]. Embryos were produced in vivo (Exp. 1 and Exp. 2) and in vitro (only Exp. 2), then transferred to recipient cows as fresh or frozen-thawed. Pregnancy was confirmed at 29 and 58 d after the end of timed ET protocol. In Exp. 1, animals had their estrous expression monitored through a tail chalk applied on the tail head of the cows and evaluated daily for chalk removal (no estrus: 100% of chalk remaining; estrus: <50% of chalk remaining). In Exp. 2, cows were continuously monitored by a leg-mounted automated activity monitor. Estrous expression was quantified using the relative increase in physical activity at estrus in relation to the days before estrus. Estrous expression was classified as no estrus [<100% relative increase in activity (RI)], weak intensity (100-299% RI), and strong intensity (≥300% RI). Data were analyzed by analysis of variance using mixed linear regression models (GLIMMIX) in SAS (SAS Institute Inc.). A total of 65.2% (914/1,401) and 89.2% (1,019/1,142) of cows from Exp. 1 and Exp. 2, respectively, displayed estrus at the end of the ovulation synchronization protocol. In Exp. 1, cows expressing estrus before to ET had greater pregnancy per ET than those that did not [41.0 ± 2.3% (381/914) vs. 31.5 ± 2.9% (151/487), respectively]. Similarly, in Exp. 2, cows classified in the strong intensity group had greater pregnancy per ET compared with cows in the weak intensity and no estrus groups [41.3 ± 2.2% (213/571) vs. 32.7 ± 2.7% (115/353) vs. 11.3 ± 3.5% (26/218), respectively]. There was no effect of ET type on pregnancy per ET in Exp. 1. However, in Exp. 2, cows that received an in vivo-produced embryo, either fresh or frozen, had greater pregnancy per ET compared with cows that received in vitro-produced embryo. Cows receiving embryos in the early blastocyst and blastocyst stage had greater fertility compared with cows receiving embryos in the morula stage. There was an interaction between the occurrence of estrus and the stage of embryo development on pregnancy per ET, cows which displayed estrus and received a morula or early blastocyst had greater pregnancy per ET than cows that did not display estrus. In conclusion, the occurrence and the intensity of estrous expression improved pregnancy per ET in recipient lactating dairy cows and thus could be used as a tool to assist in the decision making of reproduction strategies in dairy farms.

Heat Shock Protein 70 Improves In Vitro Embryo Yield and Quality from Heat Stressed Bovine Oocytes

Heat shock protein 70 (HSP70) is a chaperon that stabilizes unfolded or partially folded proteins, preventing inappropriate inter- and intramolecular interactions. Here, we examined the developmental competence of in vitro matured oocytes exposed to heat stress with or without HSP70. Bovine oocytes were matured for 24 h at 39 °C without (group C39) or with HSP70 (group H39) and at 41 °C for the first 6 h, followed by 16 h at 39 °C with (group H41) or without HSP70 (group C41). After insemination, zygotes were cultured for 9 days at 39 °C. Cleavage and embryo yield were assessed 48 h post insemination and on days 7, 8, 9, respectively. Gene expression was assessed by RT-PCR in oocytes, cumulus cells and blastocysts. In C41, blastocysts formation rate was lower than in C39 and on day 9 it was lower than in H41. In oocytes, HSP70 enhanced the expression of three HSP genes regardless of incubation temperature. HSP70 at 39 °C led to tight coordination of gene expression in oocytes and blastocysts, but not in cumulus cells. Our results imply that HSP70, by preventing apoptosis, supporting signal transduction, and increasing antioxidant protection of the embryo, protects heat stressed maturing bovine oocyte and restores its developmental competence.

Heat shock during in vitro maturation of bovine oocytes disturbs bta-miR-19b and DROSHA transcripts abundance after in vitro fertilization

While microRNAs (miRNAs) are a class of non-coding RNAs important for embryo development, the relationship between them and heat stress during oocyte maturation has not yet been established. This study investigated the effect of heat shock during in vitro maturation (IVM) on the abundance of bta-miR-20a, -27b, -103, -21-5p, -19b, -1246 miRNAs and DROSHA and DICER1 mRNAs, previously reported for being involved in oocyte maturation, response to heat stress and miRNA biogenesis. Oocytes were exposed for 12h to heat shock during IVM, fertilized in vitro and the presumptive zygotes cultured for eight days. The relative quantification of miRNAs and mRNAs was performed by real-time PCR in vitro-matured oocytes and 8-cell stage embryos. Progression of meiosis, embryonic development and apoptotic indices was also evaluated. Heat shock compromised (p < .05) oocyte nuclear maturation, cleavage and embryo development, with a higher (p < .05) embryonic apoptotic index than the control group. The abundance of bta-miR-19b increased (p < .05) whereas the abundance of DROSHA transcripts decreased (p < .05) in embryos derived from heat-shocked oocytes. In conclusion, heat shock during IVM influences the abundance of bta-miR-19b and DROSHA in pre-implantation embryos, indicating a persistent effect of heat shock that can be associated with impaired embryo development.

Heat stress on cattle embryo: gene regulation and adaptation

Global warming has been affecting animal husbandry and farming production worldwide via changes in organisms and their habitats. In the tropics, these conditions are adverse for agriculture and animal production in some areas, due to high temperatures and relative humidity, affecting competitiveness related to economic activities. These environments have deteriorated livestock production, due to periods of drought, reduction in forage quality and heat stress, eliciting negative effects on reproduction, weight gain, and reduced meat and milk production. However, the use of animals adapted to tropics such as breeds derived from subspecies Bos primigenius indicus and native breeds from tropical countries or their crossings, is an alternative to improve production under high-temperature conditions. Therefore, physiological adaptation including gene expression induced by heat stress have been studied to understand the response of animals and to improve cross-breeding between cattle breeds to maintain high productivity in adverse weather conditions. Heat stress has been associated with lower reproductive performance in cows, due to the impact on blastocyst production, decreased implantation and increased embryonic death. Thus, for decades, in vitro fertilization and embryo transfer techniques have focused on studying the optimal conditions for production of high-quality embryos to transfer. The aim of this review is to discuss the effects of heat stress in bovine embryos, and their physiological and genetic modulation, focusing on the genes that are related with major adaptability to heat stress conditions and their relationship with different embryonic stages.

Short term temperature elevation during IVM affects embryo yield and alters gene expression pattern in oocytes, cumulus cells and blastocysts in cattle

Heat stress causes subfertility in cattle by inducing alterations in steroidogenic capacity, follicular function and ovulation defects, which eventually negatively affect oocyte quality and embryo survival. Here, the effects of short, moderate temperature elevation during IVM, on embryo yield, and on the expression of various genes was evaluated. In 8 replicates, cumulus oocyte complexes (COCs) were matured for 24 h at 39 °C (controls n = 605) or at 41 °C from hour 2 to hour 8 of IVM (treated, n = 912), fertilized, and presumptive zygotes were cultured for 9 days at 39 °C. Cleavage and embryo formation rates were evaluated 48 h post insemination and on days 7, 8, 9 respectively. Cumulus cells, oocytes and blastocysts from 5 replicates were snap frozen for the relative expression analysis of genes related to metabolism, thermal and oxidative stress response, apoptosis, and placentation. In treated group, cleavage and embryo formation rates were statistically significantly lower compared with the control (cleavage 86.7% vs 74.2%; blastocysts: day 7, 29.9% vs 19.7%, day 8, 34.2% vs 22.9% and day 9 35.9% vs 24.5%). Relative mRNA abundance of three genes in cumulus cells (HSP90AA1, CPT1B, G6PD) and three genes in blastocysts (DNMT3A, PLAC8, GPX1) indicated significantly different expression between groups (p < 0.05)., The expression of G6PD, SOD2, GXP1 in oocytes and PTGS2 in blastocysts tended to differ among groups (0.05<p < 0.08). Heat stress altered (p < 0.05) the correlation of expression between HSPs and other genes in oocytes (G6PD, GPX1, CCNB1), cumulus cells (LDH, CCNB1) and blastocysts (AKR1B1, PLAC8). These results imply that exposure of oocytes to elevated temperature, even for only 6 h, disrupts the developmental competence of the oocytes, suppresses blastocyst yield and significantly alters the coordinated pattern of gene expressions.

Heat stress effects on sheep: Are hair sheep more heat resistant?

Climatic variables can trigger physiological, biochemical, haematological and hormonal alterations that influence the maintenance of homeothermy and can affect production and productivity in sheep. Different mechanisms are responsible for tolerance to heat stress (HS) including coat and skin colour, body size, fat distribution, physiological reactions and not just coat type (hair/wool). This review looks at physical, physiological, molecular and genetic aspects of heat tolerance in sheep and how they affect hair and wool sheep. We propose that it is the adaptation to hot environments and not the type of coat (wool/hair) itself that determines the capacity of the resistance of the animal to HS, due to modifications in essential pathways such as energy metabolism, physiological responses and body size. When studied in similar environments, commercial wool breeds tend to show higher heat stress, but hair breeds tend not to differ from wool breeds that are adapted to hot environments.

Prospects for gene introgression or gene editing as a strategy for reduction of the impact of heat stress on production and reproduction in cattle

In cattle, genetic variation exists in regulation of body temperature and stabilization of cellular function during heat stress. There are opportunities to reduce the impact of heat stress on cattle production by identifying the causative mutations responsible for genetic variation in thermotolerance and transferring specific alleles that confer thermotolerance to breeds not adapted to hot climates. An example of a mutation conferring superior ability to regulate body temperature is the group of frame-sift mutations in the prolactin receptor gene (PRLR) that lead to a truncated receptor and development of cattle with a short, sleek hair coat. Slick mutations in PRLR have been found in several extant breeds derived from criollo cattle. The slick mutation in Senepol cattle has been introgressed into dairy cattle in Puerto Rico, Florida and New Zealand. An example of a mutation that confers cellular protection against elevated body temperature is a deletion mutation in the promoter region of a heat shock protein 70 gene called HSPA1L. Inheritance of the mutation results in amplification of the transcriptional response of HSPA1L to heat shock and increased cell survival. The case of PRLR provides a promising example of the efficacy of the genetic approach outlined in this paper. Identification of other mutations conferring thermotolerance at the whole-animal or cellular level will lead to additional opportunities for using genetic solutions to reduce the impact of heat stress.

Embryo-maternal communication in dogs: Immune system related factors

In the bitch, establishment of pregnancy is believed to be mainly initiated by the free-floating embryo in the uterus that is under progesterone influence. As in other species, the active participation of the embryo is no longer questioned. Secretory products are transported to the embryo-maternal interface and contribute to extra-cellular matrix (ECM) degradation, a change in the intrauterine immune milieu towards a reduction of immune cells and a change in lymphocyte subsets, cell differentiation, angiogenesis, and the balance between proliferation and apoptosis. For cell-to-cell communication between embryo and maternal tissue, biomolecules inclusive microRNAs might be transported and exchanged via extracellular vesicles (EVs) as in other species. Maternal acceptance of the fetal allograft is vital for the establishment of pregnancy. Findings so far indicate that the embryo avoids attacks from the maternal system via passive and active mechanisms. One hypothesis is that expression or suppression of surface molecules help the canine embryo to hide from the maternal immune system on one side and to actively destroy cytotoxic immune cells on the other side; there are further clues that the canine embryo blocks activation of intrauterine leukocytes. Intracellular repair mechanisms via heat shock proteins (HSP) are candidates under investigation. The presence and function of immunomodulatory intrauterine cells like Treg cells and their interaction with the embryo have been intensely studied in other species but remains to be investigated in the canine preimplantation uterus.

First detection of heat shock protein 60 and 70 in the serum of early pregnant bitches

Heat shock proteins (HSPs) belong to a group of cellular stress proteins. Heat shock protein 10 immunoregulates and promotes growth during early gestation in humans, while HSP70 is considered to regulate autophagy and apoptosis during pregnancy and parturition. Both HSPs are detectable in the serum and placentas of early pregnant women and considered to contribute to the establishment of pregnancy. Within this pilot study we aimed (1) to assess whether HSPs 10, 60 and 70 are measurable in the serum of healthy early pregnant and non-pregnant bitches, and (2) to explore whether measurable differences between groups indicate pregnancy. Blood was collected from 31 bitches on days 7, 14 and 21 after mating. At 21 days post mating, all bitches were examined for pregnancy by ultrasonography; 23 were pregnant, and the eight non-pregnant bitches served as controls. Pregnant bitches had normal parturitions and gave birth to healthy puppies. The serum concentrations of HSPs 10, 60 and 70 were measured by electrophoresis and western blot. Serum HSP10 was not detectable. Average serum HSP70 concentration was significantly (d7, P = 0.030; d14, P = 0.023; d21, P = 0.030) lower in pregnant animals at all days investigated, while serum HSP60 was significantly lower at day 21 of gestation (P = 0.024) when compared to the controls. HSP 60 and HSP70 concentrations correlated positively (d7, r = +0.386, P = 0.021; d14, r = 0.450, P = 0.008; d21, r = +0.472, P = 0.006). We conclude that in pregnant bitches, serum concentrations of HSP60 and HSP70 are significantly decreased between days 7 and 21 of gestation, in comparison to non-pregnant bitches in early dioestrus, raising the question about intrauterine functions during the peri-implantation period.

Cloning: A Sleeping Beauty Awaiting the Kiss?

The first 20 years of somatic cell nuclear transfer can hardly be described as a success story. Controversially, many factors leading to the fiasco are not intrinsic features of the technique itself. Misunderstandings and baseless accusations alongside with unsupported fears and administrative barriers hampered cloners to overcome the initial challenging period with obvious difficulties that are common features of a radically new approach. In spite of some promising results of mostly sporadic and small-scale experiments, the future of cloning is still uncertain. On the other hand, a reincarnation, just like the idea of electric cars, may result in many benefits in various areas of science and economy. One can only hope that-in contrast to electric cars-the ongoing paralyzed phase will not last for 100 years, and breakthroughs achieved in some promising areas will provide enough evidence to intensify research and large-scale application of cloning in the next decade.

Regulation of heat-inducible HSPA1A gene expression during maternal-to-embryo transition and in response to heat in in vitro-produced bovine embryos

In in vitro-produced (IVP) bovine embryos, a burst in transcriptional activation of the embryonic genome (EGA) occurs at the 8-16-cell stage. To examine transcriptional regulation prior to EGA, notably in response to heat stress, we asked (1) whether the spontaneous expression of a luciferase transgene that is driven by the minimal mouse heat-shock protein 1b (hspa1b) gene promoter paralleled that of HSPA1A during EGA in IVP bovine embryo and (2) whether expression of the endogenous heat-inducible iHSPA group member HSPA1A gene and the hspa1b/luciferase transgene were induced by heat stress (HS) prior to EGA. Using two culture systems, we showed that luciferase activity levels rose during the 40-h long EGA-associated cell cycle. In contrast, iHSPA proteins were abundant in matured oocytes and in blastomeres from the two-cell to the 16-cell stages. However, normalised results detected a rise in the level of HSPA1A and luciferase mRNA during EGA, when transcription was required for their protein expression. Prior to EGA, HS-induced premature luciferase activity and transgene expression were clearly inhibited. We could not, however, establish whether this was also true for HSPA1A expression because of the decay of the abundant maternal transcripts prior to EGA. In bovine embryos, heat-induced expression of hspa1b/luciferase, and most likely of HSPA1A, was therefore strictly dependent on EGA. The level of the heat-shock transcription factor 1 molecules that were found in cell nuclei during embryonic development correlated better with the embryo's capacity for heat-shock response than with EGA-associated gene expression.

Influence of elevated temperature on bovine oviduct epithelial cells (BOECs)

The aim of this study was to evaluate the influence of elevated temperature on bovine oviduct epithelial cells (BOECs), based on the expression and localization of both heat shock protein 70 (HSP70), responsible for the cellular defence mechanism, and oviduct specific glycoprotein 1 (OVGP1) which is the most important embryotrophic protein. BOECs were cultured alone and co-cultured with cattle embryos at control (38.5°C) and elevated temperature (41°C) for 168 h. The elevated temperature had no effect on the viability of BOECs but exerted a negative effect on embryo development. The elevated temperature increased the expression of HSP70 and decreased the expression of OVGP1 at both mRNA and protein levels in BOECs cultured alone and those co-cultured with embryos. However, the presence of embryos limited the decrease in OVGP1 expression in BOECs at elevated temperature but did not alter the expression of HSP70. These results demonstrate for the first time the influence of elevated temperature on BOECs, consequently providing insights into the interactions between the embryo and the oviduct at elevated temperature.

Physiological responses of cultured bovine granulosa cells to elevated temperatures under low and high oxygen in the presence of different concentrations of melatonin

Our understanding of the effects of temperature on granulosa cell (GC) physiology is primarily limited to in vitro studies conducted under atmospheric (∼20% O₂) conditions. In the current series of factorial experiments we identify important effects of O₂ level (i.e. 5% vs 20% O₂) on GC viability and steroidogenesis, and go onto report effects of standard (37.5 °C) vs high (40.0 °C) temperatures under more physiologically representative (i.e. 5%) O₂ levels in the presence of different levels of melatonin (0, 20, 200 and 2000 pg/ml); a potent free-radical scavenger and abundant molecule within the ovarian follicle. Cells aspirated from antral (4-6 mm) follicles were cultured in fibronectin-coated wells using serum-free M199 for up to 144 h. At 37.5 °C viable cell number was enhanced and luteinization reduced under 5 vs 20% O₂. Oxygen level interacted (P < 0.001) with time in culture to affect aromatase activity and cell estradiol (E₂) production (pg/mL/10⁵ cells). These decreased between 48 and 96 h for both O₂ levels but increased again by 144 h for cells cultured under 5% but not 20% O₂. Progesterone (P₄) concentration (ng/mL/10⁵ cells) was greater (P < 0.001) under 20 vs 5% O₂ at 96 and 144 h. Cell number increased (P < 0.01) with time in culture under 5% O₂ irrespective of temperature. However, higher doses of melatonin increased viable cell number at 40.0 °C but reduced viable cell number at 37.5 °C (P = 0.004). Melatonin also reduced (P < 0.001) ROS generation at both O₂ levels across all concentrations. E₂ increased with time in culture at both temperatures under 5% O₂, however P₄ declined between 96 and 144 h at 40.0 but not 37.5 °C. Furthermore, melatonin interacted (P < 0.001) with temperature in a dose dependent manner to increase P₄ at 37.5 °C but to reduce P₄ at 40.0 °C. Transcript expression for HSD3B1 paralleled temporal changes in P₄ production, and those for HBA were greater at 5% than 20% O₂, suggesting that hemoglobin synthesis is responsive to changes in O₂ level. In conclusion, 5% O₂ enhances GC proliferation and reduces luteinization. Elevated temperatures under 5% O₂ reduce GC proliferation and P₄ production. Melatonin reduces ROS generation irrespective of O₂ level and temperature, but interacts with temperature in a dose dependent manner to influence GC proliferation and luteinization.

Effects of heat stress on bovine preimplantation embryos produced in vitro

Summer heat stress decreases the pregnancy rate in cattle and has been thought to be associated with the early embryonic death caused by the elevation of maternal body temperature. In vitro cultures have been widely used for the evaluation of effects of heat stress on oocytes, fertilization, preimplantation, and embryonic development. Susceptibility to heat stress is present in developmental stages from oocytes to cleavage-stage (before embryonic gene activation, EGA) embryos, leading to a consequent decrease in developmental competence. On the other hand, advanced-stage embryos such as morula or blastocysts have acquired thermotolerance. The mechanism for the developmental stage-dependent change in thermotolerance is considered to be the accumulation of antioxidants in embryos in response to heat-inducible production of reactive oxygen species. The supplementation of antioxidants to the culture media has been known to neutralize the detrimental effects of heat stress. Besides, EGA could be involved in acquisition of thermotolerance in later stages of embryos. Morulae or blastocysts can repair heat-induced unfolded proteins or prevent DNA damage occurring in processes such as apoptosis. Therefore, embryo transfer (ET) that can bypass the heat-sensitive stage could be a good solution to improve the pregnancy rate under heat stress. However, frozen-thawed ET could not improve the pregnancy rate as expected. Frozen-thawed blastocysts were more sensitive to heat stress and showed less proliferation upon heat exposure, compared to fresh blastocysts. Therefore, further research is required to improve the reduction in pregnancy rates due to summer heat stress.

Causes of declining fertility in dairy cows during the warm season

In the Northern Hemisphere, from June to September and in the Southern Hemisphere from December to March, there are periods of reduced fertility (sub-fertility) in dairy cows that are described as summer infertility. Several factors contribute to sub-fertility during this time, such as ambient temperature, humidity and photoperiod. During the warm season there is a reduction in feed intake that may compromise the energy balance of the cow and/or induce an imbalance in the activity of the hypothalamo-hypophyseal-ovarian axis. These factors reduce the reproductive performance of the cow and compromise the quality of oocytes, embryos and corpora lutea. This paper reviews current knowledge on the metabolic and endocrine mechanisms that induce summer infertility and describe their effects on follicle, oocyte and embryo development in dairy cows.

Pomegranate peel as a natural antioxidant enhanced reproductive performance and milk yield of female rabbits

<p>This study was designed to investigate the effects of dietary pomegranate peel (PP; 9.61% crude protein and 13.1% crude fibre) on reproductive performance and milk yield of heat-stressed rabbit does. Forty-eight V-line rabbit does with average initial live body weight of 3.59±0.11 kg (2nd parity; 9 mo old) were divided into 4 treatment  roups (12 does per group). The first group was fed diet free of PP. The second, third and fourth groups were fed diets containing 0.75, 1.5 and 3.0% PP, respectively, included in substitution of clover hay from the basal diet. Feed of the 4 groups was free of added antioxidants. The studied traits were: kindling rate, gestation period, litter size, litter weight, kit weight at both birth and weaning (28 d of lactation) for the last 3 parameters, pre-weaning mortality and milk yield. Range of temperatures and relative humidity during the experimental period in the rabbitry varied between 27.5-33.5°C and 64-76%, respectively. The inclusion of PP quadratically affected litter size at birth (P&lt;0.001) and weaning (P&lt;0.01), as well as milk yield (P&lt;0.001). However, it tended to reduce the kit milk intake in most lactation periods (P=0.078), leading to a linear reduction in individual kit weight at weaning (P=0.060). In conclusion, supplementations of PP in the diet of does during summer season in Egypt can improve their productivity.</p>

Effects of High Hydrostatic Pressure on Expression Profiles of In Vitro Produced Vitrified Bovine Blastocysts

High hydrostatic pressure (HHP) has been used to pre-condition embryos before essential, yet potentially detrimental procedures such as cryopreservation. However, the mechanisms for HHP are poorly understood. We treated bovine blastocysts with three different HHP (40, 60 and 80 MPa) in combination with three recovery periods (0, 1 h, 2 h post HHP). Re-expansion rates were significantly higher at 40 and 60 but lower at 80 MPa after vitrification-warming in the treated groups than controls. Microarray analysis revealed 399 differentially expressed transcripts, representing 254 unique genes, among different groups. Gene ontology analysis indicated that HHP at 40 and 60 MPa promoted embryo competence through down-regulation of genes in cell death and apoptosis, and up-regulation of genes in RNA processing, cellular growth and proliferation. In contrast, 80 MPa up-regulated genes in apoptosis, and down-regulated protein folding and cell cycle-related genes. Moreover, gene expression was also influenced by the length of the recovery time after HHP. The significantly over-represented categories were apoptosis and cell death in the 1 h group, and protein folding, response to unfolded protein and cell cycle in the 2 h group compared to 0 h. Taken together, HHP promotes competence of vitrified bovine blastocysts through modest transcriptional changes.

Beneficial Effects of Nitric Oxide Induced Mild Oxidative Stress on Post-Thawed Bull Semen Quality

Background

Cryopreservation of semen requires optimized conditions to minimize the harmful effects of various stresses. The main approach for protection of sperm against stress is based on the use of antioxidants and cryoprotectants, which are described as defensive methods. Recently, the application of controlled mild stressors has been de- scribed for activation of a temporary response in oocyte, embryo and somatic cells. In this study a sub-lethal oxidative stress induced by precise concentrations of nitric oxide (NO) has been evaluated for sperm during cryopreservation.

Materials and Methods

In this experimental study, we used different concentrations of NO [0 µM (NO-0), 0.01 µM (NO-0.01), 0.1 µM (NO-0.1), 1 µM (NO-1), 10 µM (NO-10) and 100 µM (NO-100)] during cryopreservation of bull semen. Their effects on post-thawed sperm quality that included motility and velocity parameters, plasma mem- brane functionality, acrosome integrity, apoptosis status, mitochondrial activity and lipid peroxidation after freezing-thawing were investigated.

Results

Exposure of sperm before freezing to NO-1 significantly increased total motility (88.4 ± 2.8%), progressive motility (50.4 ± 3.2%) and average path velocity (VAP, 53.8 ± 3.1 µm/s) compared to other extenders. In addition, NO-1 significantly increased plasma mem- brane functionality (89.3 ± 2.9%) compared to NO-0 (75.3 ± 2.9%), NO-0.01 (78.3 ± 2.9%), NO-0.1 (76.4 ± 2.9%), NO-10 (64 ± 2.9%) and NO-100 (42 ± 2.9%). Sperm exposed to NO-1 produced the highest percentage of viable (85.6 ± 2.3%) and the lowest percentage of apoptotic (10.8 ± 2.4%) spermatozoa compared to the other extenders. Also, NO-100 resulted in a higher percentage of dead spermatozoa (27.1 ± 2.7%) compared to the other extenders. In terms of mitochondrial activity, there was no significant difference among NO-0 (53.4 ± 3.2), NO-0.01 (52.1 ± 3.2), NO-0.1 (50.8 ± 3.2) and NO-1 (53.1 ± 3.2). For acrosome integrity, no significant different was observed in sperm exposed to different concentrations of NO.

Conclusion

Induction of sub-lethal oxidative stress with 1 µM NO would be beneficial for cryopreservation of bull semen.

Vitamin E status and reproduction in sheep: potential implications for Australian sheep production

Vitamin E concentrations in dried pastures, stubble and most grains are below the recommended requirement of 10–25 mg/kg dry matter (DM). Sheep grazing in an environment when dry pastures and cereal crop stubbles are their primary source of nutrients for a few months have a high risk of developing vitamin E deficiency. If the low vitamin E status coincides with late gestation, the neonate is likely to have a deficiency of vitamin E. Some of the consequences of this are well known, with nutritional myopathy (with high mortality) a risk in young growing sheep unless vitamin E supplements are provided. Vitamin E plays an important role in the management of oxidative stress. Sperm are subject to oxidative damage due to high metabolic rate and high concentration of polyunsaturated fatty acids in their membranes. Oxidative stress may also compromise follicular development and ovarian activity. Vitamin E is also involved with improvement in immune response. For these reasons, vitamin E status is important for reproductive efficiency in both males and females and in the survival of lambs and weaners. In addition, vitamin E deficiency is potentially exacerbated by a lack of other nutrients involved in the management of oxidative stress and immune function, such as selenium (Se) and sulfur amino acids. A Se concentration of 0.1 mg/kg DM in feedstuffs is required to maintain immune competency in sheep. In considering possible consequences for reproduction, further investigation is justified into: (i) effects of low vitamin E, in combination with low levels of other natural antioxidants, on the quality and quantity of sperm produced before and during mating; (ii) follicle development, fertilisation and embryonic mortality in Se-supplemented ewes; (iii) assessment of supplementing formulated antioxidants to rams and ewes during the mating season; (iv) managing oxidative stress in the newborn – consequences of large doses of vitamin E to ewes before parturition to boost lamb reserves; (v) potential benefits to lamb survival through boosting maternal innate immunity; (vi) choices for boosting antioxidant and immune function in ewes and lambs through ‘immune pack’ nutrient options that may target nutrients lacking in dry grass pastures; (vii) the potential role of heat stress in modifying the requirements for, and responses to, vitamin E in extensive grazing systems.

Astaxanthin ameliorates heat stress-induced impairment of blastocyst development in vitro:--astaxanthin colocalization with and action on mitochondria--

PURPOSE

The effects of astaxanthin (Ax) on the in vitro development of bovine embryos cultured under heat stress were investigated in combination with the assessment of its cellular accumulation and action on mitochondrial membrane potential (ΔΨm).

METHODS

Bovine ≥8-cell embryos were collected on day 3 after in vitro fertilization and exposed to single (day 4) or repeated (day 4 and 5) heat stress (10 h/day at 40.5 °C). Ax was added into culture medium under the repeated heat stress and blastocyst development was evaluated. The cellular uptake of Ax in embryos was examined using bright-field and confocal laser-scanning microscopy, and high-performance liquid chromatography. The relationship between Ax and mitochondria localization was assessed using MitoTracker dye. The effects of Ax on ΔΨm were investigated using JC-1 dye.

RESULTS

Blastocyst development in the repeated heat stress treatment decreased significantly (P < 0.05) compared with those in single heat stress or normal thermal treatment. The addition of Ax into culture medium did lead to a significant recovery in blastocyst development in the repeated heat-treated group. Ax was detected in cytoplasm of embryos and observed to colocalize with mitochondria. Ax recovered ΔΨm in embryos that was decreased by the heat treatment.

CONCLUSIONS

Ax ameliorated the heat stress-induced impairment of blastocyst development. Our results suggest that the direct action of Ax on mitochondrial activity via cellular uptake is a mechanism of the ameliorating effects.

In vitro culture of feline embryos increases stress-induced heat shock protein 70 and apoptotic related genes

Developmental competence and quality of in vitro produced embryos has been demonstrated to be lower than in vivo derived embryos. This study aimed specifically to determine the effects of in vitro culture of feline embryos using various culture densities on developmental competence and expression of stress- and apoptotic-related genes in terms of heat shock protein 70 (HSP70) and apoptotic-related (BAX and BCL-2) gene expressions. In experiment 1, we characterized the inducible form of a feline-specific HSP70 mRNA sequence, as it has not been previously reported. The primers for feline HSP70 mRNA were synthesized and tested on heat-treated cat fibroblasts. In experiment 2, feline embryos were cultured at different culture densities (embryo:culture volume; 1:1.25, 1:5 and 1:20). The developmental competence was determined along with HSP70, BAX and BCL-2 transcript abundances using quantitative RT-PCR. In vivo derived embryos were used as a control group. A partial cat HSP70 mRNA sequence (190 bp) was characterized and exhibited high nucleotide identity (93 to 96%) with other species. Cleaved embryos cultured at high density (1:1.25) developed to blastocysts at a lower rate than those generated from lower densities. Irrespective of the culture densities used, in vitro cultured blastocysts showed increased levels of HSP70 and BAX transcripts compared with in vivo counterparts. Blastocysts derived from the highest culture density (1:1.25) showed higher levels of upregulation of HSP70 and BAX transcripts than those cultured at lower culture densities (1:5 and 1:20). In conclusion, increased levels of pro-apoptotic (BAX) and stress-response (HSP70) transcripts correlated with developmental incompetence of embryos cultured at high embryonic density, indicating that stress accumulated during in vitro embryo culture affected the fate for embryo development and quality.

Obesity does not aggravate vitrification injury in mouse embryos: a prospective study

BACKGROUND

Obesity is associated with poor reproductive outcomes, but few reports have examined thawed embryo transfer in obese women. Many studies have shown that increased lipid accumulation aggravates vitrification injury in porcine and bovine embryos, but oocytes of these species have high lipid contents (63 ng and 161 ng, respectively). Almost nothing is known about lipids in human oocytes except that these cells are anecdotally known to be relatively lipid poor. In this regard, human oocytes are considered to be similar to those of the mouse, which contain approximately 4 ng total lipids/oocyte. To date, no available data show the impact of obesity on vitrification in mouse embryos. The aim of this study was to establish a murine model of maternal diet-induced obesity and to characterize the effect of obesity on vitrification by investigating the survival rate and embryo developmental competence after thawing.

METHODS

Prospective comparisons were performed between six-eight-cell embryos from obese and normal-weight mice and between fresh and vitrified embryos. Female C57BL/6 mice were fed standard rodent chow (normal-weight group) or a high-fat diet (obese group) for 6 weeks. The mice were mated, zygotes were collected from oviducts and cultured for 3 days, and six-eight-cell embryos were then selected to assess lipid content in fresh embryos and to evaluate differences in apoptosis, survival, and development rates in response to vitrification.

RESULTS

In fresh embryos from obese mice, the lipid content (0.044 vs 0.030, P<0.01) and apoptosis rate (15.1% vs.9.3%, P<0.05)were significantly higher, the survival rate (83.1% vs. 93.1%, P<0.01) on day 5 was significantly lower, and embryo development was notably delayed on days 3-5 compared with the normal-weight group. After vitrification, no significant difference was found between thawed embryos from obese and normal-weight mice in apoptosis, survival, and development rates on days 4 and 5. In both groups, pre- and post-vitrification embryo apoptosis, survival, and development rates were similar.

CONCLUSIONS

This study demonstrated that differences in survival and developmental rates between embryos from obese and normal-weight mice were eliminated after vitrification. Thus, maternal obesity does not aggravate vitrification injury, but obesity alone greatly impairs pre-implantation embryo survival and development.

Crucial surviving aspects for vitrified in vitro-produced bovine embryos

The objective of the present study was to correlate some parameters (cleavage, blastocyst production, quality degree score, total cell number, fresh apoptosis and lipid content) with embryo survival after cryopreservation. A total of 1727 in vitro-produced bovine blastocysts were used to establish the parameters (mean ± standard error of the mean (SEM)) for cleavage (85.6 ± 0.8), blastocyst production (39.9 ± 1.4), quality degree score (1.6 ± 0.1), total cell number (140.1 ± 2.9), fresh apoptosis (20.8 ± 1.1) and lipid content (21.3 ± 0.8 droplets). On the same way 1316 blastocysts were vitrified for the determination of post-cryopreservation embryo survival (49.4 ± 1.9). Fresh apoptosis rate and total lipid droplets value were correlated (P < 0.05) with embryo survival after cryopreservation (r = 0.91 and r = 0.59; respectively). However, cleavage, blastocyst production, quality degree score and total cell number were not correlated (P > 0.05) with embryo cryotolerance (r = 0.23, r = 0.38, r = 0.22 and r = 0.28; respectively). Therefore, the increased lipid content was moderately correlated with apoptosis in vitrified blastocysts. On the other hand, increased apoptosis in fresh blastocysts was strongly correlated with apoptosis in vitrified blastocysts, which indicated that the apoptosis rate in fresh embryos was a better parameter than the lipid content to predict post-vitrification embryo survival.

Terminologies for the pre-attachment bovine embryo

There are numerous publications regarding bovine embryos, ranging from descriptions of their appearance and development to emerging techniques in the field of assisted reproductive technology (ART). Concurrently, several specialized terms have been developed to describe the bovine embryo. Many of these terms are simple, some are difficult to understand and use, and others are antiquated and may not be scientifically accurate. For example, use of terms such as syngamy, conception rate, implantation and embryo resorption should be revisited. This review presents a brief overview of current knowledge regarding the pre-attachment period of the bovine embryo and attempts to define the terms. In this process, conventional terminology is presented, and contemporary and novel terms are proposed from a biological perspective.

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.

Stress preconditioning of boar spermatozoa: a new approach to enhance semen quality

Semen preparation and cryopreservation require finely adjusted procedures. Gametes are sensitive to environmental stresses, so in vitro procedures aim to minimize the inevitable harmful conditions. Applying stress to precondition cells has only been investigated recently. Studies demonstrated that by utilizing a well defined and properly applied hydrostatic pressure (HP) stress treatment to spermatozoa before in vitro storage, cryopreservation or insemination, cell survival and fertility improved compared with untreated controls. The birth of healthy piglets from treated fresh or frozen-thawed semen demonstrates the in vivo safety of the procedure. Although the biological mechanism is still unclear, several processes incorporating cellular stress response might explain the observations. This paper summarizes results, background, aspects and considerations of HP treatment for porcine semen. The new principle, i.e. to improve the stress tolerance by a defined sublethal stress may outline a new strategy in assisted reproductive technologies with unique theoretical and practical consequences.

Cells under pressure: how sublethal hydrostatic pressure stress treatment increases gametes' and embryos' performance

The principal approach in in vitro embryo culture and manipulation has been a defensive one: procedures aim to satisfy passively the supposed or real physiological needs of gametes and embryos. Similarly, during cryopreservation the aim is to cause minimal damage to cells whilst attempting to obtain the highest achievable cell survival. However, carefully chosen and precisely controlled sublethal stress treatment of cells has been described to improve embryos’ and gametes’ performance, and, as a consequence, subsequent morphological survival, fertilisation, in vitro development, pregnancy and farrowing rates improved considerably compared with untreated controls. This review summarises studies that open up a new approach: instead of – and besides – trying to passively reduce the harm to cells during in vitro manipulations and culture, procedures may also prepare the cells themselves to ward off or reduce the damage by turning up the cells’ own, inner capacities.

Developmental competence and mRNA expression of preimplantation in vitro-produced embryos from prepubertal and postpubertal cattle and their relationship with apoptosis after intraovarian administration of IGF-1

Recombinant human Insulin-like growth factor-I (hIGF-1) was administered to one ovary of prepubertal and postpubertal cattle to determine its effects on (1) oocyte developmental competence, (2) the expression pattern of six developmentally important genes (GLUT3, GLUT8, AKT1, BCL-XL, BAD, and BAX), and (3) its relationship with apoptosis (female Holstein-Friesian). Oocytes were retrieved from 7- to 10-mo-old prepubertal dairy calves (preP), 11- to 18-mo-old postpubertal heifers (postP), and cows via ultrasound-guided follicular aspiration. Immature oocytes were matured in vitro then fertilized and cultured up to the blastocyst stage. Apoptosis was determined by terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) in 8-d blastocysts. Similar low blastocyst yields were observed in the IGF-1-treated preP group (11.2+/-2.4%), the control preP group (10.4+/-3.0%), and in the IGF-1 postP group (10.9+/-2.3%). These were lower (P<or=0.01) compared with the control postP group (21.2+/-3.8%) and with cows (23+/-3.7%). The expression profile of the six genes was partly affected by age and IGF-1 treatment. Apoptosis was correlated with the age of the oocyte donors and was increased in blastocysts derived from prepubertal heifers. Results show that apoptosis is a critical feature of the acquisition of developmental competence of oocytes from prepubertal cattle and that IGF-1 did not beneficially affect oocyte developmental competence.

Factors affecting fertilisation and early embryo quality in single- and superovulated dairy cattle

Data on fertilisation and embryo quality in dairy cattle are presented and the main factors responsible for the low fertility of single-ovulating lactating cows and embryo yield in superovulated dairy cattle are highlighted. During the past 50 years, the fertility in high-producing lactating dairy cattle has decreased as milk production increased. Recent data show conception rates to first service to be approximately 32% in lactating cows, whereas in heifers it has remained above 50%. Fertilisation does not seem to be the principal factor responsible for the low fertility in single-ovulating cows, because it has remained above 80%. Conversely, early embryonic development is impaired in high-producing dairy cows, as observed by most embryonic losses occurring during the first week after fertilisation. However, in superovulated dairy cattle, although fertilisation failure is more pronounced, averaging approximately 45%, the percentage of fertilised embryos viable at 1 week is quite high (>70%). Among the multifactorial causes of low fertility in lactating dairy cows, high feed intake associated with low concentrations of circulating steroids may contribute substantially to reduced embryo quality. Fertilisation failure in superovulated cattle may be a consequence of inappropriate gamete transport due to hormonal imbalances.

Challenge testing of gametes to enhance their viability

Embryos, oocytes and spermatozoa undergo several manipulations during the in vitro procedures that are an integral part of assisted reproductive technologies (ART) in mammals. Consequently, some of the gametes are damaged irreparably, whereas others react to these challenges with some sort of survival mechanism that enables them to come through the process. The details of the mechanism remain unknown but, if identified, it could have immense potential as a new way to improve the viability of embryos produced by ART. However, few publications describe systematic ways to challenge test gametes and then to use the results as a basis for improving gamete viability. Furthermore, new methods to monitor the reactions of gametes to such challenge tests are needed. In the present review, these two issues are discussed, as are some of the conditions necessary before a challenge test protocol can be part of future work with ART.

Effects of heat stress on mammalian reproduction

Heat stress can have large effects on most aspects of reproductive function in mammals. These include disruptions in spermatogenesis and oocyte development, oocyte maturation, early embryonic development, foetal and placental growth and lactation. These deleterious effects of heat stress are the result of either the hyperthermia associated with heat stress or the physiological adjustments made by the heat-stressed animal to regulate body temperature. Many effects of elevated temperature on gametes and the early embryo involve increased production of reactive oxygen species. Genetic adaptation to heat stress is possible both with respect to regulation of body temperature and cellular resistance to elevated temperature.

Colony-stimulating factor 2 (CSF-2) improves development and posttransfer survival of bovine embryos produced in vitro

In this study, we tested the role of colony-stimulating factor 2 (CSF2) as one of the regulatory molecules that mediate maternal effects on embryonic development during the preimplantation period. Our objective was to verify effects of CSF2 on blastocyst yield, determine posttransfer survival, and evaluate properties of the blastocyst formed after CSF2 treatment. In vitro, CSF2 increased the percentage of oocytes that became morulae and blastocysts. Blastocysts that were treated with CSF2 tended to have a greater number of inner cell mass cells and had a higher ratio of inner cell mass to trophectoderm cells. There was no effect of CSF2 on the incidence of apoptosis. Treatment with CSF2 from d 5 to 7 after insemination increased embryonic survival as indicated by improved pregnancy rate at d 30-35 of gestation. Moreover, treatment with CSF2 from either d 1-7 or 5-7 after insemination reduced pregnancy loss after d 30-35. Results indicate that treatment with CSF2 can affect embryonic development and enhance embryo competence for posttransfer survival. The fact that treatment with CSF2 during such a narrow window of development altered embryonic function much later in pregnancy suggests that CSF2 may exert epigenetic effects on the developing embryo that result in persistent changes in function during the embryonic and fetal periods of development.

Prediction of embryonic developmental competence by time-lapse observation and 'shortest-half' analysis

Selecting an embryo with the highest probability of achieving a pregnancy is a major challenge. Early-cleavage embryos are considered to be of good quality; however, the exact developmental stage that predicts further development has not been defined. The aim of the study was to characterize cleavage rate and distribution of various stages of mouse preimplantation embryos using a time-lapse system. Mated mice were killed 20 h after human chorionic gonadotrophin administration and putative zygotes were recovered and cultured in an incubator-enclosed time-lapse imaging system. The 'shortest half' analysis was used to establish the period in which at least 50% of the embryonic population cleaved within the shortest time. Analysis indicated that through embryonic development, cleavage timing becomes less uniform and the 'shortest half' becomes longer with intervals of 2, 2.5, 3.5 and 5 h for 2-, 4-, 8-cell embryo and blastocyst stages, respectively. The 'shortest half' for the first cleavage was closely synchronized, with 80% of embryos developing to the blastocyst stage. Moreover, slow-cleaving embryos approaching the 2-cell stage expressed inferior developmental potential in comparison to those cleaving within the 'shortest half'. Thus, embryonic cleavage rate seems to be a biological indicator of developmental potential and may be useful for embryo selection.