Vitrification improves in-vitro embryonic survival in Bos taurus embryos without increasing pregnancy rate post embryo transfer when compared to slow-freezing: A systematic meta-analysis

Methodological approaches in vitrification: Enhancing viability of bovine oocytes and in vitro-produced embryos

Cryopreservation of bovine oocytes and embryos is essential for long-term preservation and widespread distribution of genetic material, particularly in bovine in vitro embryo production, which has witnessed substantial growth in the past decade due to advancements in reproductive biotechnologies. Among current cryopreservation methods, vitrification has emerged as the preferred cryopreservation technique over slow freezing for preserving oocytes and in vitro-produced (IVP) embryos, as it effectively addresses membrane chilling injury and ice crystal formation. Nonetheless, challenges remain and a simple and robust vitrification protocol that guarantees the efficiency and viability after warming has not yet been developed. Furthermore, although slow cooling can easily be adapted for direct transfer, an easier and more practical vitrification protocol for IVP embryos is required to allow the transfer of IVP embryos on farms using in-straw dilution. In addition, the susceptibility of bovine oocytes and embryos to cryoinjuries highlights the need for novel strategies to improve their cryotolerance. This manuscript examines various methodological approaches for increasing the viability of bovine oocytes and IVP embryos during vitrification. Strategies such as modifying lipid content or mitigating oxidative damage have shown promise in improving cryotolerance. Additionally, mathematical modelling of oocyte and embryo membrane permeability has facilitated the rational design of cryopreservation protocols, optimizing the exposure time and concentration of cryoprotectants to reduce cytotoxicity.

Recent advancements to increase success in assisted reproductive technologies in cattle

Assisted reproductive technologies (ART) are fundamental for cattle breeding and sustainable food production. Together with genomic selection, these technologies contribute to reducing the generation interval and accelerating genetic progress. In this paper, we discuss advancements in technologies used in the fertility evaluation of breeding animals, and the collection, processing, and preservation of the gametes. It is of utmost importance for the breeding industry to select dams and sires of the next generation as young as possible, as is the efficient and timely collection of gametes. There is a need for reliable and easily applicable methods to evaluate sexual maturity and fertility. Although gametes processing and preservation have been improved in recent decades, challenges are still encountered. The targeted use of sexed semen and beef semen has obliterated the production of surplus replacement heifers and bull calves from dairy breeds, markedly improving animal welfare and ethical considerations in production practices. Parallel with new technologies, many well-established technologies remain relevant, although with evolving applications. In vitro production (IVP) has become the predominant method of embryo production. Although fundamental improvements in IVP procedures have been established, the quality of IVP embryos remains inferior to their in vivo counterparts. Improvements to facilitate oocyte maturation and development of new culture systems, e.g. microfluidics, are presented in this paper. New non-invasive and objective tools are needed to select embryos for transfer. Cryopreservation of semen and embryos plays a pivotal role in the distribution of genetics, and we discuss the challenges and opportunities in this field. Finally, machine learning (ML) is gaining ground in agriculture and ART. This paper delves into the utilization of emerging technologies in ART, along with the current status, key challenges, and future prospects of ML in both research and practical applications within ART.

Factors defining developmental competence of bovine oocytes collected for in vitro embryo production†

Despite the currently relatively low effectiveness of producing bovine embryos in vitro, there is a growing interest in applying this laboratory method in the field of reproduction. Many aspects of the procedure need to be improved. One of the main problems is the inferior developmental competence of in vitro matured oocytes that are collected using the ovum pick-up method. The mechanisms of oocyte capacitation and maturation, as well as the in vivo conditions in which they grow and mature, should be carefully analyzed. A deliberate application of the identified mechanisms and beneficial factors affecting the in vitro procedures seems to be essential for achieving higher developmental competence of the oocytes that are subjected to fertilization. The results may be improved by developing and employing a laboratory maturation protocol that corresponds with appropriate preparation of donors before the ovum pick-up, an optimized hormonal treatment program, the appropriate size of ovarian follicles at the time of aspiration, and a fine-tuned coasting period.

Impact of reducing lipid content during in vitro embryo production: A systematic review and meta-analysis

There is still no consensus regarding the role of lipid modulators during in vitro embryo production. Thus, we investigated how lipid reducers during the in vitro maturation of oocytes (IVM) or in vitro culture (IVC) of embryos impact their cryotolerance. A literature search was performed using three databases, recovering 43 articles for the systematic review, comprising 75 experiments (13 performed in IVM, 62 in IVC) and testing 13 substances. In 39 % of the experiments, an increase in oocyte and/or embryo survival after cryopreservation was reported, in contrast to 48 % exhibiting no effect, 5 % causing negative effects, and 8 % influencing in a dose-dependent manner. Of the 75 experiments extracted during IVM and IVC, 41 quantified the lipid content. Of those that reduced lipid content (n = 26), 50 % increased cryotolerance, 34 % had no effect, 8 % harmed oocyte/embryo survival, and 8 % had different results depending on the concentration used. Moreover, 28 out of the 43 studies were analyzed under a meta-analytical approach at the IVC stage in cattle. There was an improvement in the cryotolerance of bovine embryos when the lipid content was reduced. Forskolin, l-carnitine, and phenazine ethosulfate positively affected cryotolerance, while conjugated linoleic acid had no effect and impaired embryonic development. Moreover, fetal bovine serum has a positive impact on cryotolerance. SOF and CR1aa IVC media improved cryotolerance, while mSOF showed no effect. In conclusion, lipid modulators did not unanimously improve cryotolerance, especially when used in IVM, but presented positive effects on cryotolerance during IVC when reaching lipid reduction.

Comparison of CellRox green fluorescence upon thawing on in vitro Bos taurus and Bos indicus embryos cryopreserved by slow freezing or vitrification

The aim of this study was to compare the levels of reactive oxygen species (ROS) in Bos taurus and Bos indicus in vitro embryos cryopreserved using either slow freezing or vitrification. Embryos were divided into four groups based on subspecies and freezing method: Bos indicus slow freezing (BiSF; n = 8), Bos indicus vitrification (BiVT; n = 10), Bos taurus slow freezing (BtSF; n = 9), and Bos taurus vitrification (BtVT; n = 6). After thawing, the embryos were incubated with CellRox Green and images were obtained using a confocal microscope. The fluorescence intensity of each cell was measured and expressed as arbitrary units of fluorescence (auf) and compared using a multiple regression and unpaired t-test with α = 0.05. Results showed that subspecies and the freezing method significantly affected auf (P < 0.001; R2 = 0.1213). Bos indicus embryos had higher auf than Bos taurus embryos, whether frozen by slow freezing (67.05 ± 23.18 vs 51.30 ± 16.84, P < 0.001) or vitrification (64.44 ± 23.32 vs 47.86 ± 17.53, P < 0.001). Slow freezing induced higher auf than vitrification in both Bos taurus (51.30 ± 16.84 vs 47.86 ± 17.53, P < 0.001) and Bos indicus (67.05 ± 23.18 vs 64.44 ± 23.32, P < 0.014). In conclusion, Bos taurus embryos had lower ROS levels when frozen using vitrification, while Bos indicus embryos had consistent ROS patterns regardless of the freezing method. However, Bos indicus embryos frozen by slow freezing tended to have a higher number of cells with elevated ROS levels.

Use of Antifreeze Protein from Tenebrio molitor (TmAFP) in Vitrification of In Vitro-Produced Bovine Embryos: An Ultrastructural Study

The objective of this study was to evaluate the effects of different concentrations of antifreeze protein (AFP) extracted from the larva of the beetle, Tenebrio molitor (TmAFP), on vitrification of in vitro-produced bovine embryos. In vitro-produced blastocysts were divided into three experimental groups and vitrified using a cryotop. TmAFP was added to the equilibrium solution (ES) and vitrification solution (VS) at a concentration of 0 ng/mL (control), 500 ng/mL (500TmAFP), or 1000 ng/mL (1000TmAFP). Vitrification was carried out by first placing the blastocysts in ES for 2 minutes (7.5% ethylene glycol [EG] and 7.5% dimethyl sulfoxide [DMSO]). The blastocysts were then transferred to VS (15% EG and 15% DMSO) and promptly deposited on a cryotop stem and submerged in liquid nitrogen. Warming was carried out in three steps with decreasing sucrose concentrations. After warming, the blast cells were cultured for 24 hours for subsequent survival analysis and ultrastructural evaluation. There was a significant difference in the survival rate and expansion in the 500TmAFP group compared with the other groups. The ultrastructural analysis revealed intracellular lesions in all vitrified embryos; however, the embryos of the 500TmAFP and 1000TmAFP groups showed fewer cytoplasmic lesions compared with the control group. Taken together, addition of TmAFP can mitigate cellular changes that involve organelles and cellular components essential for proper functioning and improve the viability of warmed and vitrified in vitro-produced bovine embryos.

Mitochondrial bioenergetic profiles of warmed bovine blastocysts are typically altered after cryopreservation by slow freezing and vitrification

The widespread use of cryopreserved in vitro produced (IVP) bovine embryos is limited due to their low post-warming viability compared to their ex vivo derived counterparts. Therefore, the present study aimed to analyse in detail the consequences of cryopreservation (vitrification and slow freezing) on the bioenergetic profile of the embryo and its mitochondria. To accomplish that, day 7 IVP embryos were separated in a non-cryopreserved control group (fresh, n = 120, 12 replicates) or were either slow frozen (slow frozen, n = 60, 6 replicates) or vitrified (vitrified, n = 60, 6 replicates). An in-depth analysis of the bioenergetic profiles was then performed on these 3 groups, analysing pools of 10 embryos revealing that embryo cryopreservation both via vitrification and slow freezing causes profound changes in the bioenergetic profile of bovine embryos. Noteworthy, fresh embryos demonstrate a significantly (P < 0.05) higher oxygen consumption rate (OCR) compared to vitrified and slow frozen counterparts (0.858 ± 0.039 vs. 0.635 ± 0.048 vs. 0.775 ± 0.046 pmol/min/embryo). This was found to be largely due to significantly reduced mitochondrial oxygen consumption in both vitrified and deep-frozen embryos compared to fresh counterparts (0.541 ± 0.057 vs. 0.689 ± 0.044 vs. 0.808 ± 0.025 pmol/min/embryo). Conversely, slow-frozen thawed blastocysts showed 1.8-fold (P < 0.05) higher non-mitochondrial OCR rates compared to fresh embryos. Maximum mitochondrial respiration of vitrified and slow-frozen embryos was significantly reduced by almost 1.6-fold compared to fresh embryos and the proportion of ATP-linked respiration showed significantly lower values in vitrified thawed embryos compared to fresh embryos (1.1-fold, P < 0.05). Likewise, vitrification-warming and freeze-thawing reduced reactive glycolytic capacity (1.4 fold, 1.2-fold)as well as compensatory glycolytic capacity to provide energy in response to mitochondrial deficiency (1.3-fold and 1.2-fold, P < 0.05). In conclusion, the present study has, to the best of our knowledge, identified for the first time a comprehensive overview of typical altered metabolic features of the bioenergetic profile of bovine embryos after cryopreservation, which have great potential to explain the detrimental effects of cryopreservation on embryo viability. Avoidance of these detrimental effects through technical improvements is therefore suggested to be mandatory to improve the viability of bovine embryos after cryopreservation-warming.

Low oxygen tension during in vitro embryo production improves the yield, quality, and cryotolerance of bovine blastocysts

Mammalian oocytes undergo maturation and fertilization in the low-oxygen (O2) environment of the oviduct. To evaluate the effect of O2 tension during in vitro maturation and fertilization on embryo yield, quality, cryotolerance, and gene expression, we matured and fertilized bovine cumulus-oocyte complexes under low (5%) or high (20%) O2 tension. Presumptive zygotes from both groups were cultured at 5% O2 for 8 days. Blastocysts were vitrified, and then warmed, and cultured for further 24 h to assess their cryotolerance. Our findings indicate that low O2 during maturation and fertilization enhances embryo development and cell count in both fresh and vitrified/warmed blastocysts. In this study, the interaction of O2 tension and status (fresh or vitrified/warmed) affected the transcript abundance of SOD2, AQP3, and BAX in blastocysts. These results highlight the role of low O2 tension during bovine maturation and fertilization and provide support to using 5% O2 throughout all stages of bovine in vitro embryo production.

Genome-Wide Association (GWAS) Applied to Carcass and Meat Traits of Nellore Cattle

The meat market has enormous importance for the world economy, and the quality of the product offered to the consumer is fundamental for the success of the sector. In this study, we analyzed a database which contained information on 2470 animals from a commercial farm in the state of São Paulo, Brazil. Of this total, 2181 animals were genotyped, using 777,962 single-nucleotide polymorphisms (SNPs). After quality control analysis, 468,321 SNPs provided information on the number of genotyped animals. Genome-wide association analyses (GWAS) were performed for the characteristics of the rib eye area (REA), subcutaneous fat thickness (SFT), shear force at 7 days' ageing (SF7), and intramuscular fat (IMF), with the aid of the single-step genomic best linear unbiased prediction (ssGBLUP) method, with the purpose of identifying possible genomic windows (~1 Mb) responsible for explaining at least 0.5% of the genetic variance of the traits under analysis (≥0.5%). These genomic regions were used in a gene search and enrichment analyses using MeSH terms. The distributed heritability coefficients were 0.14, 0.20, 0.18, and 0.21 for REA, SFT, SF7, and IMF, respectively. The GWAS results indicated significant genomic windows for the traits of interest in a total of 17 chromosomes. Enrichment analyses showed the following significant terms (FDR ≤ 0.05) associated with the characteristics under study: for the REA, heat stress disorders and life cycle stages; for SFT, insulin and nonesterified fatty acids; for SF7, apoptosis and heat shock proteins (HSP27); and for IMF, metalloproteinase 2. In addition, KEGG (Kyoto encyclopedia of genes and genomes) enrichment analysis allowed us to highlight important metabolic pathways related to the studied phenotypes, such as the growth hormone synthesis, insulin-signaling, fatty acid metabolism, and ABC transporter pathways. The results obtained provide a better understanding of the molecular processes involved in the expression of the studied characteristics and may contribute to the design of selection strategies and future studies aimed at improving the productivity of Nellore cattle.

A recently developed minimum volume, absorbent, vitrification device, the Kitasato Vitrification System gives excellent outcomes for in vitro produced bovine blastocysts

Cryopreservation of embryos is a crucial component of current assisted reproductive technologies (ART). While the ART outcomes for many species have been greatly improved by the introduction of minimum volume vitrification devices, these devices can be difficult to handle and load. To reduce this problem, we recently developed a vitrification carrier which has a highly absorbent surface so that it simply and rapidly removes excess free vitrification solution from the specimen before the cooling step. This Kitasato Vitrification System (KVS) gives excellent results for human and mouse embryo vitrification. This study aimed to determine whether the KVS would also be effective for bovine blastocyst vitrification by comparing outcomes for the control device that was the KVS without excess vitrification solution absorber. The effect of varying the length of time spent in the first equilibration solution (0-10 min) was also evaluated. Vitrification with the KVS resulted in significantly higher survival and hatching rates than with the control device loaded with the same volume of vitrification solution (survival: 98.6% vs 87.6%, hatching at 72 h post warming: 87.3% vs 66.7%, respectively). The best outcomes were obtained with a 10 min equilibration step prior to exposure to the vitrification solution for 30 s. We also evaluated the effect of embryo quality on blastocyst viability when using the KVS. Survival rates of high- and low-quality embryos were comparable but low quality embryos had significantly lower hatching rates. Overall, the results indicate that the KVS vitrification device is effective for bovine blastocyst vitrification.

Effects of antifreeze protein from Lolium perenne L. (LpAFP) in the vitrification of in vitro-produced bovine embryos

In the present study, the cryoprotective effects of Lolium perenne antifreeze protein (LpAFP) on the vitrification of bovine embryos were evaluated. In vitro-produced blastocysts were divided into two groups: the control group (CG) without the addition of LpAFP and the treatment group (TG) with the addition of 500 ng/ml of LpAFP in the equilibrium and vitrification solution. Vitrification was carried out by transferring the blastocysts to the equilibrium solution [7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO)] for 2 min and then to the vitrification solution (15% EG, 15% DMSO and 0.5M sucrose). The blastocysts were deposited on a cryotop device and submerged in liquid nitrogen. Warming was carried out in three steps in solutions with different sucrose concentrations (1.0, 0.5, and 0.0 M, respectively). Embryos were evaluated for re-expansion/hatching, the total cell count, and ultrastructural analysis. There was no significant difference in the re-expansion rate 24 h after warming; however, there was variation (P < 0.05) in the hatching rate in the TG and the total number of cells 24 h after warming was higher in the TG (114.87 ± 7.24) when compared with the CG (91.81 ± 4.94). The ultrastructural analysis showed changes in organelles related to the vitrification process but, in the TG, there was less damage to mitochondria and rough endoplasmic reticulum compared with the CG. In conclusion, the addition of 500 ng/ml of LpAFP during the vitrification of in vitro-produced bovine embryos improved the hatching rate and total cell number of blastocysts after warming and mitigated intracellular damage.

Cryopreservation increases accumulation of exogenous stearic acid in mouse embryos

Cryopreservation of preimplantation embryos is a widely used technique, but this procedure might impact the subsequent embryo development. The effect of slow freezing and vitrification on the lipid metabolism in preimplantation mammalian embryos is not well studied. In this work, we applied Raman spectroscopy of isotopically labeled molecules to address the effects of cryopreservation on fatty acid accumulation in mouse embryos. Embryos after slow freezing or vitrification were cultured for 20 h in a medium supplemented with bovine serum albumin saturated with deuterated stearic acid (dSA). After this period the concentration of dSA estimated from Raman spectra of frozen-thawed and vitrified-warmed embryos at the morula stage was almost twice higher compared to non-cryopreserved morulas. At the same time, frozen-thawed and vitrified-warmed 4-cell embryos did not demonstrate any difference in the level of stearic acid uptake from non-cryopreserved embryos of the same stage. After an additional 24 h culture, cryopreserved and non-cryopreserved embryos demonstrated similar dSA uptake.

Fitness of calves born from in vitro-produced fresh and cryopreserved embryos

In cattle, vitrified/warmed (V/W) and frozen/thawed (F/T), in vitro-produced (IVP) embryos, differ in their physiology and survival from fresh embryos. In this study, we analyzed the effects of embryo cryopreservation techniques on the offspring. IVP embryos cultured with albumin and with or without 0.1% serum until Day 6, and thereafter in single culture without protein, were transferred to recipients on Day 7 as F/T, V/W, or fresh, resulting in N = 24, 14, and 13 calves, respectively. Calves were clinically examined at birth, and blood was analyzed before and after colostrum intake (Day 0), and subsequently on Day 15 and Day 30. On Day 0, calves from V/W and F/T embryos showed increased creatinine and capillary refill time (CRT) and reduced heartbeats. Calves from F/T embryos showed lower PCO₂, hemoglobin, and packed cell volume than calves from V/W embryos while V/W embryos led to calves with increased Na⁺ levels. Colostrum effects did not differ between calves from fresh and cryopreserved embryos, indicating similar adaptive ability among calves. However, PCO₂ did not decrease in calves from V/W embryos after colostrum intake. Serum in culture led to calves with affected (P < 0.05) temperature, CRT, HCO 3 - , base excess (BE), TCO₂, creatinine, urea, and anion gap. On Day 15, the effects of embryo cryopreservation disappeared among calves. In contrast, Day 30 values were influenced by diarrhea appearance, mainly in calves from V/W embryos (i.e., lower values of TCO₂, HCO 3 - , and BE; and increased glucose, anion gap, and lactate), although with no more clinical compromise than calves from fresh and F/T embryos. Diarrhea affected PCO₂ and Na⁺ in all groups. Embryo cryopreservation, and/or culture, yield metabolically different calves, including effects on protein and acid-base metabolism.

Advantages of vitrification preservation in assisted reproduction and potential influences on imprinted genes

Cryopreservation has important application in assisted reproductive technology (ART). The vitrification technique has been widely used in the cryopreservation of oocytes and embryos, as a large number of clinical results and experimental studies have shown that vitrification can achieve a higher cell survival rate and preimplantation development rate and better pregnancy outcomes. Ovarian tissue vitrification is an alternative method to slow freezing that causes comparatively less damage to the original follicular DNA. At present, sperm preservation mainly adopts slow freezing or rapid freezing (LN2 vapor method), although the vitrification method can achieve higher sperm motility after warming. However, due to the use of high-concentration cryoprotectants and ultra-rapid cooling, vitrification may cause strong stress to gametes, embryos and tissue cells, resulting in potentially adverse effects. Imprinted genes are regulated by epigenetic modifications, including DNA methylation, and show single allele expression. Their accurate regulation and correct expression are very important for the placenta, fetal development and offspring health. Considering that genome imprinting is very sensitive to changes in the external environment, we comprehensively summarized the effect of cryopreservation—especially the vitrification method in ART—on imprinted genes. Animal studies have found that the vitrification of oocytes and embryos can have a significant impact on some imprinted genes and DNA methylation, but the few studies in humans have reported almost no influence, which need to be further explored. This review provides useful information for the safety assessment and further optimization of the current cryopreservation techniques in ART.

Pregnancy of Cryopreserved Ovine Embryos at Different Developmental Stages

BACKGROUND: Developmental stage and cryopreservation method have significant impact on the pregnancy rate after transfer of embryos produced in vivo. OBJECTIVE: To determine the pregnancy outcomes from ovine embryos cryopreserved at different developmental stages. MATERIALS AND METHODS: Embryos at different developmental stages were obtained from donor ewes through simultaneous estrus treatment and laparoscopic artificial insemination. Embryos, either cryopreserved via vitrification or slow freezing method, were implanted into recipient ewes. The pregnancy rate was determined 35 days after transfer. RESULTS: The pregnancy rate of developing embryos increases after transfer from the morula stage, early blastocyst to expanded blastocyst stages (64.9%, 73.9% and 81.3%, respectively). However, cryopreservation significantly decreases the pregnancy rate of embryos at all three developmental stages, and there is no significant difference among developmental stages (43.9%, 43.7%, 52.9%, respectively). There is also no significant difference in the pregnancy rate between slowly-frozen embryos and vitrified embryos. CONCLUSION: The pregnancy outcomes of embryo transfer is better at the expanded blastocyst stage than at earlier stages. However, no difference is observed in the pregnancy rate of embryos at different developmental stage after cryopreservation, either by slow freezing and vitrification. Cryopreservation methods for ovine embryos, both slow freezing and vitrification, need further improvement.

Specifics of vitrification of in vitro-produced cattle embyos at various development stages

Producing embryos in vitro is an important technology used to improve the genetic potential of cattle and perfect the programs of their breeding. Regardless of the way they are produced, all embryos that had not been used for transplantation to recipients must be conserved. Because of significantly increased interest in the problem of cryoconservation of embryos, both coming from scientists and businesses, there are emerging new commercial environments that allow the facilitation of cryoconservation and the increase in the embryo survival. Oocyte-cumulus complexes obtained from the ovaries of slaughtered clinically healthy cows matured in 22–24 h in in vitro conditions. The oocytes were co-cultured with spermatozoids in Fertilization medium, and the obtained zygotes were cultured in Culture medium with Sodium-Pyruvate for 4 or 7 days up to the stage of morula or blastocyste, respectively. For the vitrification of cow embryos, we used a commercial kit for the vitrification of human embryos, having compared the duration of equilibration. According to the results of the studies, we observed high efficiency of cryoconservation of cow embryos using the commercial kit for vitrification of human embryos. The results revealed the significant effect of equilibration on survival and further development of embryos. In addition, we described the dependence of development stage of cattle embryo on the duration of the contact of embryo with equilibration solution. Therefore, optimal time of contact of cattle embryos at the morula stage with equilibration solution was 12 minutes. On the 24th h after thawing, 46.7 ± 3.3% of the embryos were observed to undergo blastulation, and on 48th h, this parameter increased to 96.7 ± 3.3%, which corresponded to the parameters in the group of embryos that had not been subjected to cryoconservation. In the conditions of further cultivation, the percentage of blastocystes that hatched in the experimental group was no different from that of the control. At the same time, the highest efficiency of vitrification of blastocystes of cows was seen after the contact with the equilibration solution for 15 min, since the percentage of hatched blastocystes was the same as in the control group. Therefore, using the commercial kit for vitrification of human embryos is beneficial, for it promotes the parameters of cow embryos after vitrification/thawing that are similar to such of intact embryos (without freezing). The data we analyzed and presented in the paper could help to increase the efficiency of cryoconservation of cattle embryos for both scientific and commercial purposes.