Cellular and epigenetic changes induced by heat stress in bovine preimplantation embryos

Quantification of the effect of in utero events on lifetime resilience in dairy cows

Currently, the dairy industry is facing many challenges that could affect its sustainability, including climate change and public perception of the industry. As a result, interest is increasing in the concept of identifying resilient animals, those with a long productive lifespan, as well as good reproductive performance and milk yield. There is much evidence that events in utero, that is, the developmental origins of health and disease hypothesis, alter the life-course health of offspring and we hypothesized that these could alter resilience in calves, where resilience is identified using lifetime data. The aim of this study was to quantify lifetime resilience scores (LRS) using an existing scoring system, based on longevity with secondary corrections for age at first calving and calving interval, and to quantify the effects of in utero events on the LRS using 2 datasets. The first was a large dataset of cattle on 83 farms in Great Britain born from 2006 to 2015 and the second was a smaller, more granular dataset of cattle born between 2003 and 2015 in the Langhill research herd at Scotland's Rural College. Events during dam's pregnancy included health events (lameness, mastitis, use of an antibiotic or anti-inflammatory medication), the effect of heat stress as measured by temperature-humidity index, and perturbations in milk yield and quality (somatic cell count, percentage fat, percentage protein and fat:protein ratio). Daughters born to dams that experienced higher temperature-humidity indexes while they were in utero during the first and third trimesters of pregnancy had lower LRS. Daughter LRS were also lower where milk yields or median fat percentages in the first trimester were low, and when milk yields were high in the third trimester. Dam LRS was positively associated with LRS of their offspring; however, as parity of the dam increased, LRS of their calves decreased. Similarly, in the Langhill herd, dams of a higher parity produced calves with lower LRS. Additionally, dams that recorded a high maximum locomotion score in the third trimester of pregnancy were negatively associated with lower calf LRS in the Langhill herd. Our results suggest that events that occur during pregnancy have lifelong consequences for the calf's lifetime performance. However, experience of higher temperature-humidity indexes, higher dam LRS, and mothers in higher parities explained a relatively small proportion of variation in offspring LRS, which suggests that other factors play a substantial role in determining calf LRS. Although "big data" can contain a considerable amount of noise, similar findings between the 2 datasets indicate it is likely these findings are real.

In Vitro Embryos of Romosinuano and Tropical Milking Cattle during Three Seasons in Veracruz, Mexico

One of the main factors that influences the fertility of cattle in grazing systems in hot tropical climates is heat stress. The objective of this study was to evaluate the effect of season, breed, hormonal and physiological condition on the quantity and quality of cumulus-oocyte complexes (COCs) and embryos produced in vitro, from Romosinuano (RM) and Tropical Milking (TM) donors. Three ovum pick-up and in vitro fertilization (OPU-IVF) were performed, one per season: hot dry (HD; 10, 10), hot humid (HH; 9, 9) and fresh dry (FD; 7, 10) in RM and LT donors. Serum levels of cortisol, insulin and glucose were measured, in addition to heart rate (HR), respiratory rate (RR) and rectal temperature (RT). Effect of season x genotype interaction (p ≤ 0.05) was observed in all COC variables and only in cleavage embryos (CLI) (p ≤ 0.05). Body weight (BW) affected all COC variables (p ≤ 0.01), except unviable (UNV) although affected degenerated embryos (DEG) (p ≤ 0.01) and total blastocysts (BLAST) (p ≤ 0.01). Cow age only affected viable COCs (VIAB) (p ≤ 0.05), code one blastocysts (BC1) and BLAST (p ≤ 0.01). Cortisol affected total COCs (COCsT), VIAB and total matured in vitro (TMIV) (p ≤ 0.01), as well as CLI, BC1 (p ≤ 0.01) and BLAST (p ≤ 0.05). Insulin affected COCsT (p ≤ 0.01), UNV (p ≤ 0.05), denuded oocytes (DE) (p ≤ 0.01), BC1 and code two blastocysts (BC2) (p ≤ 0.01). Glucose affected all COC variables (p ≤ 0.01), except UNV and all embryo variables except BC2. HR affected COCsT, DE, TMIV (p ≤ 0.01), CLI, BLAST and DEG (p ≤ 0.05). RR affected COCsT, UNV, VIAB, CLI (p ≤ 0.05), BC1, BLAST and DEG (p ≤ 0.01). RT only affected DE, VIAB (p ≤ 0.01) and BLAST (p ≤ 0.05). The seasonal climatic year variation of Veracruz and changes in physiological and hormonal variables have diverse effects on the cumulus-oocyte complexes and embryos produced by RM and TM donors.

Heat-Stress Impacts on Developing Bovine Oocytes: Unraveling Epigenetic Changes, Oxidative Stress, and Developmental Resilience

Extreme temperature during summer may lead to heat stress in cattle and compromise their productivity. It also poses detrimental impacts on the developmental capacity of bovine budding oocytes, which halt their fertility. To mitigate the adverse effects of heat stress, it is necessary to investigate the mechanisms through which it affects the developmental capacity of oocytes. The primary goal of this study was to investigate the impact of heat stress on the epigenetic modifications in bovine oocytes and embryos, as well as on oocyte developmental capacity, reactive oxygen species, mitochondrial membrane potential, apoptosis, transzonal projections, and gene expression levels. Our results showed that heat stress significantly reduced the expression levels of the epigenetic modifications from histone H1, histone H2A, histone H2B, histone H4, DNA methylation, and DNA hydroxymethylation at all stages of the oocyte and embryo. Similarly, heat stress significantly reduced cleavage rate, blastocyst rate, oocyte mitochondrial-membrane potential level, adenosine-triphosphate (ATP) level, mitochondrial DNA copy number, and transzonal projection level. It was also found that heat stress affected mitochondrial distribution in oocytes and significantly increased reactive oxygen species, apoptosis levels and mitochondrial autophagy levels. Our findings suggest that heat stress significantly impacts the expression levels of genes related to oocyte developmental ability, the cytoskeleton, mitochondrial function, and epigenetic modification, lowering their competence during the summer season.

An expert review of environmental heat exposure and stillbirth in the face of climate change: Clinical implications and priority issues

Exposure to extreme heat in pregnancy increases the risk of stillbirth. Progress in reducing stillbirth rates has stalled, and populations are increasingly exposed to high temperatures and climate events that may further undermine health strategies. This narrative review summarises the current clinical and epidemiological evidence of the impact of maternal heat exposure on stillbirth risk. Out of 20 studies, 19 found an association between heat and stillbirth risk. Recent studies based in low- to middle-income countries and tropical settings add to the existing literature to demonstrate that all populations are at risk. Additionally, both short-term heat exposure and whole-pregnancy heat exposure increase the risk of stillbirth. A definitive threshold of effect has not been identified, as most studies define exposure as above the 90th centile of the usual temperature for that population. Therefore, the association between heat and stillbirth has been found with exposures from as low as >12.64°C up to >46.4°C. The pathophysiological pathways by which maternal heat exposure may lead to stillbirth, based on human and animal studies, include both placental and embryonic or fetal impacts. Although evidence gaps remain and further research is needed to characterise these mechanistic pathways in more detail, preliminary evidence suggests epigenetic changes, alteration in imprinted genes, congenital abnormalities, reduction in placental blood flow, size and function all play a part. Finally, we explore this topic from a public health perspective; we discuss and evaluate the current public health guidance on minimising the risk of extreme heat in the community. There is limited pregnancy-specific guidance within heatwave planning, and no evidence-based interventions have been established to prevent poor pregnancy outcomes. We highlight priority research questions to move forward in the field and specifically note the urgent need for evidence-based interventions that are sustainable.

Developmental programming of production and reproduction in dairy cows: II. Association of gestational stage of maternal exposure to heat stress with offspring's birth weight, milk yield, reproductive performance and AMH concentration during the first lactation period

Although the negative effect of maternal exposure to heat stress on production and reproduction of offspring has been reported, there are some discrepancies among various studies about which gestational stage is more critical in this regard. Therefore, the present research was conducted to identify during which stage(s) of pregnancy maternal exposure to heat stress would lead to more dramatic decrease in productive and reproductive performance of offspring. To this end, offspring were classified based on the gestational stage they were in utero exposed to heat stress into four categories, including heat stress exposure (HSE) during only the first trimester of gestation (HSE1), HSE during the first and second trimester of gestation (HSE2), HSE during the second and third trimester of gestation (HSE3) and HSE during only the third trimester of gestation (HSE4). In study I, data of birth weight, milk yield and reproductive variables of 11,788 offspring and data of the month they were conceived were retrieved. In study II, blood samples (n = 521) were collected from offspring in various categories of HSE for measurement of serum AMH. Offspring in HSE1 and HSE2 categories were heavier than offspring in HSE3 and HSE4 categories (P < 0.0001). Offspring in HSE1 and HSE3 categories had the lowest and highest milk production, respectively (P < 0.05). First service conception rate was the greatest and worst in HSE1 and HSE4 categories, respectively (P < 0.05). Service per conception and calving to conception interval were greater in HSE2 than HSE4 category (P < 0.05). Concentration of AMH was lower in HSE1 than HSE4 category (P < 0.05). In conclusion, the present study indicated that the early stage of gestation could be a more critical period for the negative impact of in utero heat stress on developmental programming of milk production and ovarian reserves. Yet an evident temporal pattern for the adverse effect of maternal heat stress on developmental programming of reproductive performance in offspring was not found.

Molecular, enzymatic responses and in vitro embryonic developmental competency of heat-shocked buffalo embryos co-cultured with granulosa cells monolayer

The present study was designed to establish a suitable alternative approach to mitigate the adverse effect of high culture temperature on in vitro embryo development and the related molecular response in buffalo. Pre-cultured granulosa cells (GCs) were used as a monolayer during in vitro embryo culture until day 8 (day of fertilization = D0). Post fertilization, presumptive embryos were randomly assigned into two culture conditions: embryos cultured in the presence of GCs monolayer under normal culture temperature (N: 38.5 °C; GEN group) or heat shock (H: 40.5 °C; GEH group) and their counterpart groups of embryos cultured without GCs (EN and EH groups). Additionally, two groups of GCs monolayer were cultured without embryos up to day 8 under 38.5 °C (GN) or 40.5 °C (GH) for further spent culture media enzymatic analyses. Heat shock was administered for the first 2 h of culture then continued at 38.5 °C until day 8. The results indicated that under heat treatment, GCs enhanced (P ≤ 0.05) embryo cleavage and development (day 8) rates, which were comparable to the embryos cultured at 38.5 °C. On the molecular level, blastocysts of the GEH group showed similar expressions of metabolism-regulating genes (CPT2 and SlC2A1/GLUT1) and an antioxidant gene (SOD2) when compared to the blastocysts of the EN group. The relative expression of HSP90 was significantly up-regulated under heat shock and/or co-culture conditions. However, HSF1 expression was increased (P ≤ 0.05) in the GEH group. No statistical differences were observed among the study groups for the pluripotency gene NANOG, and stress resistance transcript NFE2L2. Regarding the enzymatic profile, the concentrations of SOD, total protein, and MDA were decreased (P ≤ 0.05) in the GEH group compared to the cultured GCs without embryos (GH group). In conclusion, GCs as a monolayer have a beneficial impact on alleviating heat stress at the zygote stage through the regulatory mechanisms of metabolic activity, defense system, and heat shock response genes.

Candidate genes associated with heat stress and breeding strategies to relieve its effects in dairy cattle: a deeper insight into the genetic architecture and immune response to heat stress

The need for food products of animal origin is increasing worldwide. Satisfying these needs in a way that has minimal impact on the environment requires cutting-edge technologies and techniques to enhance the genetic quality of cattle. Heat stress (HS), in particular, is affecting dairy cattle with increasing frequency and severity. As future climatic challenges become more evident, identifying dairy cows that are more tolerant to HS will be important for breeding dairy herds that are better adapted to future environmental conditions and for supporting the sustainability of dairy farming. While research into the genetics of HS in the context of the effect of global warming on dairy cattle is gaining momentum, the specific genomic regions involved in heat tolerance are still not well documented. Advances in omics information, QTL mapping, transcriptome profiling and genome-wide association studies (GWAS) have identified genomic regions and variants associated with tolerance to HS. Such studies could provide deeper insights into the genetic basis for response to HS and make an important contribution to future breeding for heat tolerance, which will help to offset the adverse effects of HS in dairy cattle. Overall, there is a great interest in identifying candidate genes and the proportion of genetic variation associated with heat tolerance in dairy cattle, and this area of research is currently very active worldwide. This review provides comprehensive information pertaining to some of the notable recent studies on the genetic architecture of HS in dairy cattle, with particular emphasis on the identified candidate genes associated with heat tolerance in dairy cattle. Since effective breeding programs require optimal knowledge of the impaired immunity and associated health complications caused by HS, the underlying mechanisms by which HS modulates the immune response and renders animals susceptible to various health disorders are explained. In addition, future breeding strategies to relieve HS in dairy cattle and improve their welfare while maintaining milk production are discussed.

Transgenerational transmission of environmental effects in livestock in the age of global warming

Recent decades provide mounting evidence for the continual increase in global temperatures, now termed "global warming," to the point of drastic worldwide change in the climate. Climatic change is a long-term shift in temperatures and weather patterns, including increased frequency and intensity of extreme environmental events such as heat waves accompanied by extreme temperatures and high humidity. Climate change and global warming put several challenges to the livestock industry by directly affecting the animal's production, reproduction, health, and welfare. The broad impact of global warming, and in particular heat stress, on-farm animals' performance has been comprehensively studied. It has been estimated that the US livestock industry's loss caused by heat stress is up to $2.4 billion annually. However, the long-term intergenerational and transgenerational effects of climatic change and global warming on farm animals are sparse. Transgenerational effects, which are mediated by epigenetic mechanisms, can affect the animal's performance regardless of its immediate environment by altering its phenotypic expression to fit its ancestors' environment. In many animal species, environmental effects are epigenetically encoded within a narrow time interval during the organism's gametogenesis, and these epigenetic modifications can then be intergenerationally transmitted. Several epigenetic mechanisms mediate intergenerational transmission of environmental effects, typically in a parent-dependent manner. Therefore, exposure of the animal to an extreme climatic event and other environmental stressors during gametogenesis can undergo epigenetic stabilization in the germline and be passed to the offspring. As a result, the offspring might express a phenotype adjusted to fit the stressors experienced by their ancestors, regardless of their direct environment. The purpose of this perspective is to review current evidence for intergenerational and transgenerational transmission of environmental stress effects, specifically in the context of global warming and climate change, and to offer viewpoints on the possible impacts on the livestock industry.

Short heat shock has a long-term effect on mesenchymal stem cells' transcriptome

The adverse effects of heat stress (HS) on physiological systems are well documented, yet the underlying molecular mechanisms behind it remain poorly understood. To address this knowledge gap, we conducted a comprehensive investigation into the impact of HS on mesenchymal stem cells (MSCs), focusing on their morphology, phenotype, proliferative capacity, and fate determination. Our in-depth analysis of the MSCs' transcriptome revealed a significant influence of HS on the transcriptional landscape. Notably, even after a short period of stress, we observed a persistent alteration in cell identity, potentially mediated by the activation of bivalent genes. Furthermore, by comparing the differentially expressed genes following short HS with their transcriptional state after recovery, we identified the transient upregulation of MLL and other histone modifiers, providing a potential mechanistic explanation for the stable activation of bivalent genes. This could be used to predict and modify the long-term effect of HS on cell identity.

Heat Stress as a Barrier to Successful Reproduction and Potential Alleviation Strategies in Cattle

In recent decades, the adverse effects of global warming on all living beings have been unanimously recognized across the world. A high environmental temperature that increases the respiration and rectal temperature of cattle is called heat stress (HS), and it can affect both male and female reproductive functions. For successful reproduction and fertilization, mature and healthy oocytes are crucial; however, HS reduces the developmental competence of oocytes, which compromises reproduction. HS disturbs the hormonal balance that plays a crucial role in successful reproduction, particularly in reducing the luteinizing hormone and progesterone levels, which leads to severe problems such as poor follicle development with a poor-quality oocyte and problems related to maturity, silent estrus, abnormal or weak embryo development, and pregnancy loss, resulting in a declining reproduction rate and losses for the cattle industry. Lactating cattle are particularly susceptible to HS and, hence, their reproduction rate is substantially reduced. Additionally, bulls are also affected by HS; during summer, semen quality and sperm motility decline, leading to compromised reproduction. In summer, the conception rate is reduced by 20-30% worldwide. Although various techniques, such as the provision of water sprinklers, shade, and air conditioning, are used during summer, these methods are insufficient to recover the normal reproduction rate and, therefore, special attention is needed to improve reproductive efficiency and minimize the detrimental effect of HS on cattle during summer. The application of advanced reproductive technologies such as the production of embryos in vitro, cryopreservation during the hot season, embryo transfer, and timed artificial insemination may minimize the detrimental effects of HS on livestock reproduction and recover the losses in the cattle industry.

Effects of Heat Stress on Bovine Oocytes and Early Embryonic Development-An Update

Heat stress is a major threat to cattle reproduction today. It has been shown that the effect of high temperature not only has a negative effect on the hormonal balance, but also directly affects the quality of oocytes, disrupting the function of mitochondria, fragmenting their DNA and changing their maternal transcription. Studies suggest that the induction of HSP70 may reduce the apoptosis of granular layer cells caused by heat stress. It has been shown that the changes at the transcriptome level caused by heat stress are consistent with 46.4% of blastocyst development disorders. Cows from calves exposed to thermal stress in utero have a lower milk yield in their lifetime, exhibit immunological disorders, have a lower birth weight and display a shorter lifespan related to the expedited aging. In order to protect cow reproduction, the effects of heat stress at the intracellular and molecular levels should be tracked step by step, and the impacts of the dysregulation of thermal homeostasis (i.e., hyperthermy) should be taken into account.

Oxidative Stress and Oocyte Cryopreservation: Recent Advances in Mitigation Strategies Involving Antioxidants

Oocyte cryopreservation is widely used in assisted-reproductive technology and animal production. However, cryopreservation not only induces a massive accumulation of reactive oxygen species (ROS) in oocytes, but also leads to oxidative-stress-inflicted damage to mitochondria and the endoplasmic reticulum. These stresses lead to damage to the spindle, DNA, proteins, and lipids, ultimately reducing the developmental potential of oocytes both in vitro and in vivo. Although oocytes can mitigate oxidative stress via intrinsic antioxidant systems, the formation of ribonucleoprotein granules, mitophagy, and the cryopreservation-inflicted oxidative damage cannot be completely eliminated. Therefore, exogenous antioxidants such as melatonin and resveratrol are widely used in oocyte cryopreservation to reduce oxidative damage through direct or indirect scavenging of ROS. In this review, we discuss analysis of various oxidative stresses induced by oocyte cryopreservation, the impact of antioxidants against oxidative damage, and their underlying mechanisms. We hope that this literature review can provide a reference for improving the efficiency of oocyte cryopreservation.

Nutritional Modulation, Gut, and Omics Crosstalk in Ruminants

Simple Summary

Over the last decade, animal nutrition science has been significantly developed, supported by the great advancements in molecular technologies. For scientists, the present "feedomics and nutrigenomics" era continues to evolve and shape how research is designed, performed, and understood. The new omics interpretations have established a new point of view for the nutrition–gene interaction, integrating more comprehensive findings from animal physiology, molecular genetics, and biochemistry. In the ruminant model, this modern approach addresses rumen microbes as a critical intermediate that can deepen the studies of diet–gut interaction with host genomics. The present review discusses nutrigenomics’ and feedomics’ potential contribution to diminishing the knowledge gap about the DNA cellular activities of different nutrients. It also presents how nutritional management can influence the epigenetic pathway, considering the production type, life stage, and species for more sustainable ruminant nutrition strategies.

Abstract

Ruminant nutrition has significantly revolutionized a new and prodigious molecular approach in livestock sciences over the last decade. Wide-spectrum advances in DNA and RNA technologies and analysis have produced a wealth of data that have shifted the research threshold scheme to a more affluent level. Recently, the published literature has pointed out the nutrient roles in different cellular genomic alterations among different ruminant species, besides the interactions with other factors, such as age, type, and breed. Additionally, it has addressed rumen microbes within the gut health and productivity context, which has made interpreting homogenous evidence more complicated. As a more systematic approach, nutrigenomics can identify how genomics interacts with nutrition and other variables linked to animal performance. Such findings should contribute to crystallizing powerful interpretations correlating feeding management with ruminant production and health through genomics. This review will present a road-mapping discussion of promising trends in ruminant nutrigenomics as a reference for phenotype expression through multi-level omics changes.

Genetic parameters and weighted single-step genome-wide association study for supernumerary teats in Holstein cattle

Supernumerary teats (SNT) are a common epidermal abnormality of udders in mammals. The SNT negatively affect machine milking ability, udder health, and animal welfare and sometimes act as reservoirs for undesirable bacteria, resulting in economic losses on calves and lactating cows due to the cost of SNT removal surgery, early culling, and low milk yield. This study aimed to analyze the incidence and genetic parameter of SNT and detect SNT-related genes in Chinese Holstein cattle. In this study, the incidence of SNT was recorded in 4,670 Chinese Holstein cattle (born between 2008 and 2017) from 2 farms, including 734 genotyped cows with 114,485 SNPs. The SNT had a total frequency of 9.8% and estimated heritability of 0.22 (SE = 0.07), which were obtained using a threshold model in the studied Chinese Holstein population. Furthermore, we calculated approximate genetic correlations between SNT and the following indicator traits: 12 milk production, 28 body conformation, 5 fertility and reproduction, 5 health, and 9 longevity. Generally, the estimated correlations, such as 305-d milk yield for third parity (-0.55; SE = 0.02) and age at first calving in heifer (0.19; SE = 0.03), were low to moderate. A single-step GWAS was implemented, and 10 genes associated with SNT located in BTA4 were identified. The region (112.70-112.90 Mb) on BTA4 showed the highest genetic variance for SNT. The quantitative trait loci on BTA4 was mapped into the RARRES2 gene, which was previously shown to affect adipogenesis and hormone secretion. The WIF1 gene, which was located in BTA5, was also considered as a candidate gene for SNT. Overall, these findings provide useful information for breeders who are interested in reducing SNT.

Comparative CpG methylation kinetic patterns of cis-regulatory regions of heat stress-related genes in Sahiwal and Frieswal cattle upon persistent heat stress

The kinetic patterns of CpG methylation of the cis-regulatory region of heat stress-related genes on exposed to heat stress (at 42 °C) between the Sahiwal and Frieswal cattle was compared in the present study. Using an in vitro whole blood culture model, cells were continuously exposed to heat stress (at 42 °C) for 6 h. Methylation levels of five genes, viz., GPX1, HSP70, HSP90, c-FOS, and JUN were estimated by SyberGreen-based quantitative methylation-specific PCR (qMSP) assay. CpG methylation kinetics at different time points of heat stress (0.5, 1, 2, 4, 6 h) were analyzed using mixed ANOVA. The initial methylation level, estimated at 37 °C, of HSP70 was significantly high in the Sahiwal breed. A significant (p<0.001) time-dependent hypomethylation of an antioxidant gene (GPX1) CpG islands was detected at the acute phase of the stress. Heat shock protein gene (HSP70) showed a similar CpG methylation kinetics where the hypomethylation was prominent from 1 h and persisted up to 4 h. The heat stress responses of both Sahiwal and Frieswal cattle were identical as there was no distinctiveness in the methylation kinetics of CpG islands of studied genes. The acclimatization of Frieswal cattle-a breed developed in India over the years to the tropical climatic conditions, maybe one of the reasons for this similarity. Thus, the present study results could pave a path to understand the molecular mechanism of heat stress and adaptation of indigenous and crossbred cattle populations to the changing scenario in tropical climate conditions.

Conjugated linoleic acid improves meiotic spindle morphology and developmental competence of heat-stressed bovine oocyte

This study was conducted to elucidate the effects of introducing conjugated linoleic acid (CLA) on meiotic spindle organization of heat stressed (HS) matured oocytes and the resulting blastocysts DNA methylation as well as the expression of the genes involved in DNA methylation (DNMT3a, DNMT3b and DNMT1). Immature bovine oocytes were cultured at 41 °C for the first 12 h and 38.5 °C for the second 12 h of maturation time in the presence of 0 and 50 μM of CLA (HS and HS + CLA groups, respectively). A group of oocytes cultured in medium with no CLA supplementation at normal temperature (38.5 °C for 24 h) was considered as negative control (C). Percentage of normal spindle, and cleavage and blastocyst rates were significantly decreased in the HS group compared to the C group (P < 0.05). The global DNA methylation and expression level of DNMT3a gene were increased in HS group compared to the C groups (P < 0.05), while the expression level of DNMT3b was decreased. The CLA supplementation improved the percentage of normal microtubules shape in MII oocytes as well as the developmental competence in the HS + CLA group compared to the HS group (P < 0.05). However, global DNA methylation and expression level of DNMT3a/b were not ameliorated by CLA supplementation (P > 0.05). Based on the obtained results, CLA proved to be capable of improving the oocyte developmental competence as well as decreased the aberrant spindle organization of heat-stressed oocytes and it would not cause epigenetic alteration in the obtained blastocysts.

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.

Impacts of Epigenetic Processes on the Health and Productivity of Livestock

The dynamic changes in the epigenome resulting from the intricate interactions of genetic and environmental factors play crucial roles in individual growth and development. Numerous studies in plants, rodents, and humans have provided evidence of the regulatory roles of epigenetic processes in health and disease. There is increasing pressure to increase livestock production in light of increasing food needs of an expanding human population and environment challenges, but there is limited related epigenetic data on livestock to complement genomic information and support advances in improvement breeding and health management. This review examines the recent discoveries on epigenetic processes due to DNA methylation, histone modification, and chromatin remodeling and their impacts on health and production traits in farm animals, including bovine, swine, sheep, goat, and poultry species. Most of the reports focused on epigenome profiling at the genome-wide or specific genic regions in response to developmental processes, environmental stressors, nutrition, and disease pathogens. The bulk of available data mainly characterized the epigenetic markers in tissues/organs or in relation to traits and detection of epigenetic regulatory mechanisms underlying livestock phenotype diversity. However, available data is inadequate to support gainful exploitation of epigenetic processes for improved animal health and productivity management. Increased research effort, which is vital to elucidate how epigenetic mechanisms affect the health and productivity of livestock, is currently limited due to several factors including lack of adequate analytical tools. In this review, we (1) summarize available evidence of the impacts of epigenetic processes on livestock production and health traits, (2) discuss the application of epigenetics data in livestock production, and (3) present gaps in livestock epigenetics research. Knowledge of the epigenetic factors influencing livestock health and productivity is vital for the management and improvement of livestock productivity.

Thermal-treatment protocol to induce thermotolerance in bovine embryos

Artificial reproduction in dairy cattle is challenged by summer temperatures in tropical environments. We describe a treatment based on mild temperature increases to induce thermotolerance and improve the embryo's performance under heat stress conditions. A protocol was established to induce upregulation of heat shock protein A (HSPA, formerly known as HSP70) but not impair embryonic development. Thermal treatment (TT) had no effect on morula/blastocyst rate or blastocyst quality (cell number and apoptosis). Heat shock given one day after TT revealed higher (P=0.00) survival rates in TT blastocysts compared with Control. Treated embryos were transferred to recipients and no detrimental effects were observed regarding pregnancy rates, length, fetal growth or calf weight. Our results demonstrated that the established TT protocol could induce a thermal response by the embryo and is safe for further development.

Senescence and Apoptosis During in vitro Embryo Development in a Bovine Model

According to the World Health Organization, infertility affects up to 14% of couples under reproductive age, leading to an exponential rise in the use of assisted reproduction as a route for conceiving a baby. In the same way, thousands of embryos are produced in cattle and other farm animals annually, leading to increased numbers of individuals born. All reproductive manipulations entail deviations of natural phenotypes and genotypes, with in vitro embryo technologies perhaps showing the biggest effects, although these alterations are still emerging. Most of these indications have been provided by animal models, in particular the bovine species, due to its similarities to human early embryo development. Oocytes and embryos are highly sensitive to environmental stress in vivo and in vitro. Thus, during in vitro culture, a number of stressful conditions affect embryonic quality and viability, inducing subfertility and/or long-term consequences that may reach the offspring. A high proportion of the embryos produced in vitro are arrested at a species-specific stage of development during the first cell divisions. These arrested embryos do not show signs of programmed cell death during early cleavage stages. Instead, defective in vitro produced embryos would enter a permanent cell cycle arrest compatible with cellular senescence, in which they show active metabolism and high reactive oxygen species levels. Later in development, mainly during the morula and blastocyst stages, apoptosis would mediate the elimination of certain cells, accomplishing both a physiological role in to balancing cell proliferation and death, and a pathological role preventing the transmission of damaged cells with an altered genome. The latter would acquire relevant importance in in vitro produced embryos that are submitted to stressful environmental stimuli. In this article, we review the mechanisms mediating apoptosis and senescence during early embryo development, with a focus on in vitro produced bovine embryos. Additionally, we shed light on the protective role of senescence and apoptosis to ensure that unhealthy cells and early embryos do not progress in development, avoiding long-term detrimental effects.

Equine blastocyst production under different incubation temperatures and different CO2 concentrations during early cleavage

Some basic parameters for equine invitro embryo production have not yet been established, including the optimum temperature for maturation and embryo culture, and the optimum CO2 concentration and pH during early embryo development. To explore this, we first performed cultures in incubators set at 37.2°C, 37.7°C or 38.2°C. At these temperatures, the corresponding maturation rates were 33%, 38% and 42%; cleavage rates were 84%, 86% and 88%; and blastocyst rates were 35%, 44% and 44% per injected oocyte. These rates did not differ significantly (P>0.2). We then evaluated three different CO2 concentrations (6%, 6.5% or 7% CO2) in 5% O2 for culture over Days 0-5 after intracytoplasmic sperm injection, using a commercial human embryo medium with added serum, at 38.2°C. The pH values of these media were 7.36, 7.33 and 7.29 respectively. In the presence of 6%, 6.5% or 7% CO2, cleavage rates were 68%, 80% and 70% respectively, and blastocyst rates per injected oocyte were 42%, 54% and 27% respectively. The blastocyst rate for the 7% CO2 treatment was significantly lower than that for the 6.5% CO2 treatment (P<0.05). We conclude that equine invitro embryo production is equally effective within the range of 37.2-38.2°C, but that equine early cleavage stage development is sensitive to small changes in CO2 atmosphere and/or medium pH.

Cellular and functional adaptation to thermal stress in ovarian granulosa cells in mammals

Climate change represents a significant environmental challenge to human welfare. One of many negative impacts may be on animal reproduction. Elevated ambient temperature unfavourably influences reproductive processes in mammals. High temperature can affect reproductive processes such as follicle development and may alter follicular fluid concentrations of amino acids, fatty acids, minerals, enzymes, antioxidants defence and growth factors. These impacts may lead to inferior oocyte competence and abnormal granulosa cell (GCs) function. Mammalian oocytes are enclosed by GCs that secret hormones and signalling molecules to promote oocyte competence. GCs are essential for proper follicular development, oocyte maturation, ovulation, and luteinization. Many environmental stressors, including thermal stress, affect GC function and alter oocyte development and growth. Several studies documented a link between elevated ambient temperature and increased generation of cellular reactive oxygen species (ROS). ROS can damage DNA, reduce cell proliferation, and induce apoptosis in GCs, thus altering oocyte development. Additionally, thermal stress induces upregulation of thermal shock proteins, such as HSP70 and HSP90. This review provides an update on the influence of thermal stress on GCs of mammals. Discussions include impacts to steroidogenesis (estradiol and progesterone), proliferation and cell cycle transition, apoptosis, oxidative stress (ROS), antioxidants related genes, heat shock proteins (HSPs) and endoplasmic reticulum responses.

Ochratoxin A exposure causes meiotic failure and oocyte deterioration in mice

Ochratoxin A (OTA) is a mycotoxin produced by fungi and occurs naturally in various foodstuffs and some animal-derived products. This mycotoxin can cause deleterious effects on kidney, liver, central nervous, and immune system. However, potential mechanisms regarding how OTA disrupts the mammalian oocyte quality have not been clearly defined. In this study, we proved that OTA weakened oocyte quality by impairing oocyte meiotic maturation. We found that female mice treated with 1 mg/kg body weight OTA by intraperitoneal (IP) injection for 7 days displayed ovarian dysfunction and decreased offspring number. We also found that OTA treatment at 7.5 μM for 16 h decreased the rate of first polar body extrusion by disrupting spindle and chromosome alignment. In addition, OTA caused oxidative stress by inducing the accumulation of reactive oxygen species and consumption of antioxidants during meiosis, consequently resulting in oocytes apoptosis. Mitochondrial damage and insufficient energy supply were also observed in OTA-pretreated oocytes, which led to the meiotic failure of oocyte. Moreover, the epigenetic modifications were also affected, showing with altered 5 mC, 5hmC, H3K9ac, and H3K9me3 levels in mice oocytes. In summary, these results showed that OTA could decrease oocyte maturation and fertility by inducing oxidative stress and epigenetic changes.

DNA methylation, environmental exposures and early embryo development

The first crucial step in the developmental program occurs during pre-implantation, the time after the oocyte has been fertilized and before the embryo implants in the uterus. This period represents a vulnerable window as the epigenome undergoes dynamic changes in DNA methylation profiles. Alterations in the early embryonic reprogramming wave can impair DNA methylation patterns and induce permanent changes to the developmental program, leading to the onset of adverse health outcomes in offspring. Although there is an increasing body of evidence indicating that harmful exposures during pre-implantation embryo development can trigger lasting epigenetic alterations in offspring, the mechanisms are still not fully understood. Since physiological or pathological changes in DNA methylation can occur as a response to environmental cues, proper environmental milieu plays a critical role in the success of embryonic development. In this review, we depict the mechanisms behind the embryonic epigenetic reprogramming of DNA methylation and highlight how maternal environmental stressors (e.g., alcohol, heat stress, nutrient availability) during pre-implantation and assisted reproductive technology procedures affect development and DNA methylation marks.

Invited review: Management strategies capable of improving the reproductive performance of heat-stressed dairy cattle

Impaired fertility during periods of heat stress is the culmination of numerous physiological responses to heat stress, ranging from reduced estrus expression and altered follicular function to early embryonic death. Furthermore, heat-stressed dairy cattle exhibit a unique metabolic status that likely contributes to the observed reduction in fertility. An understanding of this unique physiological response can be used as a basis for improving cow management strategies, thereby reducing the negative effects of heat stress on reproduction. Potential opportunities for improving the management of dairy cattle during heat stress vary greatly and include feed additives, targeted cooling, genetic selection, embryo transfer and, potentially, crossbreeding. Previous studies indicate that dietary interventions such as melatonin and chromium supplementation could alleviate some of the detrimental effects of heat stress on fertility, and that factors involved in the methionine cycle would likely do the same. These supplements, particularly chromium, may improve reproductive performance during heat stress by alleviating insulin-mediated damage to the follicle and its enclosed cumulus-oocyte complex. Beyond feed additives, some of the simplest, yet most effective strategies involve altering the timing of feeding and cooling to take advantage of comparatively low nighttime temperatures. Likewise, expansion of cooling systems to include breeding-age heifers and dry cows has significant benefits for dams and their offspring. More complicated but promising strategies involve the calculation of breeding values for thermotolerance, the identification of genomic markers for heat tolerance, and the development of bedding-based conductive cooling systems. Unfortunately, no single approach can completely rescue the fertility of lactating dairy cows during heat stress. That said, region-appropriate combinations of strategies can improve reproductive measures to reasonable levels.

Heat stress, a serious threat to reproductive function in animals and humans

Global warming represents a major stressful environmental condition that compromises the reproductive efficiency of animals and humans via a rise of body temperature above its physiological homeothermic point (heat stress [HS]). The injuries caused by HS on reproductive function involves both male and female components, fertilization mechanisms as well as the early and late stages of embryo-fetal development. This occurrence causes great economic damage in livestock, and, in wild animals creates selective pressure towards the advantages of better-adapted genotypes to the detriment of others. Humans undergo several types of stress, including heat, and these represent putative causes of ongoing progressive decay in procreation; an increasing number of remedies in the form of antioxidant preparations are now being proposed to counteract the effects of stress. This review aims to describe the results of the most recent studies that aimed to highlight these effects and to draw information on the mechanisms acting as the basis of this problem from a comparative analysis.