Effect of addition of l-carnitine to media for oocyte maturation and embryo culture on development and cryotolerance of bovine embryos produced in vitro

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.

The effect of L-carnitine supplementation during in vitro maturation on oocyte maturation and somatic cloned embryo development

The quality of the recipient cytoplasm was reported as a crucial factor in maintaining the vitality of SCNT embryos and SCNT efficiency for dairy cows. Compared with oocytes matured in vivo, oocytes matured in vitro showed abnormal accumulation and metabolism of cytoplasmic lipids. L-carnitine treatment was found to control fatty acid transport into the mitochondrial β-oxidation pathway, which improved the process of lipid metabolism. The results of this study show that 0.5 mg/ml L-carnitine significantly reduced the cytoplasmic lipid content relative to control. No significant difference was observed in the rate of oocyte nuclear maturation, but the in vitro developmental competence of SCNT embryos was improved in terms of increased blastocyst production and lower apoptotic index in the L-carnitine treatment group. In addition, the pregnancy rate with SCNT embryos in the treatment group was significantly higher than in the control group. In conclusion, the present study demonstrated that adding L-carnitine to the maturation culture medium could improve the developmental competence of SCNT embryos both in vitro and in vivo by reducing the lipid content of the recipient cytoplasm.

Biomarker metabolite mating of viable frozen-thawed in vitro-produced bovine embryos with pregnancy-competent recipients leads to improved birth rates

Selection of competent recipients before embryo transfer (ET) is indispensable for improving pregnancy and birth rates in cattle. However, pregnancy prediction can fail when the competence of the embryo is ignored. We hypothesized that the pregnancy potential of biomarkers could improve with information on embryonic competence. In vitro-produced embryos cultured singly for 24 h (from d 6 to 7) were transferred to d 7 synchronized recipients as fresh or after freezing and thawing. Recipient blood was collected on d 0 (estrus; n = 108) and d 7 (4-6 h before ET; n = 107) and plasma was analyzed by nuclear magnetic resonance (1H+NMR). Spent embryo culture medium (CM) was collected and analyzed by ultra-high-performance liquid chromatography tandem mass spectrometry in a subset of n = 70 samples. Concentrations of metabolites quantified in plasma (n = 35) were statistically analyzed as a function of pregnancy diagnosed on d 40, d 62 and birth. Univariate analysis with plasma metabolites consisted of a block study with controllable fixed factors (i.e., embryo cryopreservation, recipient breed, and day of blood collection; Wilcoxon test and t-test). Metabolite concentrations in recipients and embryos were independently analyzed by iterations that reclassified embryos or recipients using the support vector machine. Iterations identified some competent embryos, but mostly competent recipients that had a pregnancy incompetent partner embryo. Misclassified recipients that could be classified as competent were reanalyzed in a new iteration to improve the predictive model. After subsequent iterations, the predictive potential of recipient biomarkers was recalculated. On d 0, creatine, acetone and l-phenylalanine were the most relevant biomarkers at d 40, d 62, and birth, and on d 7, l-glutamine, l-lysine, and ornithine. Creatine was the most representative biomarker within blocks (n = 20), with a uniform distribution over pregnancy endpoints and type of embryos. Biomarkers showed higher abundance on d 7 than d 0, were more predictive for d 40 and d 62 than at birth, and the pregnancy predictive ability was lower with frozen-thawed (F-T) embryos. Six metabolic pathways differed between d 40 pregnant recipients for fresh and F-T embryos. Within F-T embryos, more recipients were misclassified, probably due to pregnancy losses, but were accurately identified when combined with embryonic metabolite signals. After recalculation, 12 biomarkers increased receiver operator characteristic-area under the curve (>0.65) at birth, highlighting creatine (receiver operator characteristic-area under the curve = 0.851), and 5 new biomarkers were identified. Combining metabolic information of recipient and embryos improves the confidence and accuracy of single biomarkers.

L-carnitine enhances developmental potential of bovine oocytes matured under high lipid concentrations in vitro

Maternal obesity elevates non-esterified fatty acids (NEFA) follicular concentrations. Bovine cumulus-oocyte complexes (COCs) matured in vitro under high NEFA have altered metabolism and reduced quality. Systemically, obesity promotes altered mitochondrial metabolism linked to L-carnitine insufficiency. We hypothesized that L-carnitine supplementation during IVM of bovine COCs in the presence of high NEFA would lessen the negative effects of exposure to excessive lipids on embryonic development and oxidative stress. COCs were collected from abattoir ovaries and matured in four groups: CON (control), LC (3 mM L-carnitine), HN (high NEFA: 200uM oleic, 150uM palmitic and 75uM stearic acid), and HNLC (HN and LC). Mature oocytes were assayed for aerobic and anaerobic metabolism utilizing oxygen and pH microsensors or fertilized in vitro (D0). Cleavage (D3) and blastocyst (D7, D8) rates were assessed. D3 embryos with ≥ 4 cells were stained for cytosolic and mitochondrial ROS. D8 blastocysts were assayed for gene transcript abundance of metabolic enzymes. Oocyte metabolism was not affected by IVM treatment. D3 formation of embryos with ≥ 4 cells were lower in LC or HN than CON or HNLC; blastocyst rates were greater for CON and lower for HN than LC and HNLC. D3 embryo mitochondrial and cytosolic ROS were reduced in HNLC when compared to other groups. IVM in HN altered blastocyst gene transcript abundance when compared to CON, but not LC or HNLC. In conclusion, supplementation with L-carnitine protects oocytes exposed to high NEFA during IVM and improves their developmental competence, suggesting that high lipid exposure may lead to L-carnitine insufficiency in bovine oocytes.

Factors Affecting the Efficiency of In Vitro Embryo Production in Prepubertal Mediterranean Water Buffalo

Embryos from prepubertal water buffalo can be produced using laparoscopic ovum pickup (LOPU) and in vitro embryo production (IVEP). However, to date, it is unclear what factors and environmental conditions can affect LOPU-IVEP efficiency in prepubertal animals, especially buffalo. In this study, we explored the impact of season, age and individual variation among female donor animals, as well as the effect of the sire used for in vitro fertilization. Donor animals between 2 and 6 months of age were stimulated using gonadotropins prior to LOPU, which was performed at two-week intervals. Following in vitro maturation and fertilization, the resulting embryos were then cultured to the blastocyst stage until they were either vitrified or transferred into recipient animals. The number of follicles available for aspiration and embryo development rates was stable throughout the year. As animals became older, there was a slight trend for fewer COCs recovered from LOPU and better embryo development. There was a large individual variation in both ovarian response and the developmental competence of oocytes among donors. The bull used for fertilization also had a significant impact on embryo development. Upon embryo transfer, pregnancy rates were not affected by the number of embryos transferred per recipient. The best pregnancy rates were achieved when transferring blastocysts, compared to compact morula or hatched blastocysts. Finally, vitrification had no effect on pregnancy rate compared to fresh embryos.

Actions of FGF2, LIF, and IGF1 on bovine embryo survival and conceptus elongation following slow-rate freezing

Culture environment during in vitro embryo production can affect embryo phenotype and pregnancy outcomes, making culture modifications a logical approach for improving embryo competence. Previously, the addition of the growth factors FGF2, LIF, and IGF1, termed FLI, to the culture medium improved bovine embryo development, and re-expansion following cryopreservation. The objective of this study was to investigate the survival of cryopreserved FLI treated embryos at day 15 of pregnancy and evaluate conceptus transcriptomes. Embryos were produced using in vitro fertilization of abattoir-derived oocytes, cultured to the blastocyst stage in the presence or absence of FLI (+/- FLI), and cryopreserved by slow-rate freezing. Thawed embryos were transferred into non-lactating recipient beef cows and eight days later conceptuses were recovered and analyzed. For a subset of conceptuses whole transcriptome analysis was performed by using the NovaSeq 6000. There was no detectable difference in conceptus recovery or average conceptus length between the two groups. There were 32 differentially expressed transcripts, 23 up-regulated and nine down-regulated in the +FLI group compared to -FLI. Genes were involved in interferon signaling, prostaglandin synthesis, and placental development. This study reveals that embryos cultured with or without FLI and cryopreserved by slow-rate freezing have similar developmental competence up to day 15 of development. Nevertheless, differences in gene expression exhibit an effect of FLI on conceptus signaling during elongation.

Carnitines as Mitochondrial Modulators of Oocyte and Embryo Bioenergetics

Recently, the importance of bioenergetics in the reproductive process has emerged. For its energetic demand, the oocyte relies on numerous mitochondria, whose activity increases during embryo development under a fine regulation to limit ROS production. Healthy oocyte mitochondria require a balance of pyruvate and fatty acid oxidation. Transport of activated fatty acids into mitochondria requires carnitine. In this regard, the interest in the role of carnitines as mitochondrial modulators in oocyte and embryos is increasing. Carnitine pool includes the un-esterified l-carnitine (LC) and carnitine esters, such as acetyl-l-carnitine (ALC) and propionyl-l-carnitine (PLC). In this review, carnitine medium supplementation for counteracting energetic and redox unbalance during in vitro culture and cryopreservation is reported. Although most studies have focused on LC, there is new evidence that the addition of ALC and/or PLC may boost LC effects. Pathways activated by carnitines include antiapoptotic, antiglycative, antioxidant, and antiinflammatory signaling. Nevertheless, the potential of carnitine to improve energetic metabolism and oocyte and embryo competence remains poorly investigated. The importance of carnitine as a mitochondrial modulator may suggest that this molecule may exert a beneficial role in ovarian disfunctions associated with metabolic and mitochondrial alterations, including PCOS and reproductive aging.

Treatment of mouse cumulus-oocyte complexes with L-carnitine during vitrification and in vitro maturation affects maturation and embryonic developmental rate after parthenogenetic activation

The technique of oocyte vitrification remains a challenge in most animal species. The present study aimed to evaluate the effects of cumulus cell presence and L-carnitine (LC) treatment during vitrification of selected immature oocytes by brilliant cresyl blue (BCB) staining on maturation and embryonic developmental rate after parthenogenetic activation. Immature oocytes were obtained from C57BL/6 female mice ovaries and stained with BCB. The BCB⁺ cumulus-oocyte complexes (COCs) were then selected and random parts of COCs were denuded from cumulus cells (denuded oocytes: DOs). COCs and DOs were treated with/out LC (0.6 mg/ml) during vitrification and in vitro maturation (IVM) procedures. A number of non-vitrified COCs were also treated with LC during the IVM process (fresh group). Maturation rate, intracellular glutathione (GSH) contents, and developmental competence of oocytes were also examined. The GSH levels in vitrified DOs+LC and vitrified COCs+LC groups were significantly higher (p < 0.01) than untreated vitrified-warmed COCs and DOs. Maturation rate and blastocyst developmental rate were reduced after the vitrification-warming procedure compared with the fresh group. The vitrified COCs+LC group showed a higher percentage of mature oocytes and the ability to develop to blastocyst stage than the vitrified-warmed DOs group (p < 0.01). These data indicated that the presence of cumulus cells around the competent oocyte and LC treatment during vitrification and IVM procedure could improve parthenogenetic developmental competence of vitrified-warmed oocytes by increasing GSH levels and accelerating oocyte maturation.

Biological roles of l-carnitine in oocyte and early embryo development

Poor oocyte quality is responsible for female infertility. Multiple studies have been carried out to find supplements to enhance oocyte quality and mitigate infertility problems. l-carnitine and its derivatives have diverse roles in developing oocytes and early embryos. This review focuses on the in vitro and in vivo studies that using l-carnitine alone or in combination with other supplements for oocyte quality enhancement. The key roles of l-carnitine in oocyte quality and embryo growth were summarized, and the underlying mechanism was also elucidated. l-carnitine helps in the lipid metabolism process by controlling the transfer of fatty acids to mitochondria for β-oxidation. l-carnitine modulates glucose metabolism and enhances respiratory chain enzyme activity. Furthermore, it acts as an antioxidant to prevent oxidative damage and inhibit apoptosis, a signal in response to oxidative stress. Results show the potential of l-carnitine as a potential agent in assisted reproductive technology to improve oocyte quality and the subsequent embryonic development.

Modulation of lipid metabolism through multiple pathways during oocyte maturation and embryo culture in bovine

Lipid accumulation occurs in cultured embryos and is associated with reduced cryotolerance. Here we report the use of a multiple pathway lipid modulator cocktail (l-carnitine, linoleic acid and forskolin) to improve cryosurvival. First, we stained oocytes and embryos with Oil Red to examine the time course of lipid accumulation during in vitro fertilization (IVF) and embryo culture. Then we evaluated the effects of the lipid modulators cocktail on lipid content, developmental rates and survival after vitrification. In our conditions, lipid accumulation was detected (P < 0.05) at the end of in vitro maturation (IVM) and after 4 days of embryo culture (D4-D5). In experiment 1, we used lipid modulator cocktail during IVM. Reduced (P < 0.05) lipid accumulation was detected in oocytes (Control: 49.9 ± 1.6, Lip. Mod. IVM: 45.0 ± 1.8) but no changes were present at blastocyst stage (Control: 62.4 ± 2.6, Lip. Mod. IVM: 66.8 ± 2.7). Treated oocytes presented decreased (P < 0.05) blastocyst rates and lower (P < 0.05) re-expansion after vitrification. In experiment 2, lipid modulators cocktail was used during embryo culture (from D4-D7 or D6-D7). Treatment had an effect on lipid metabolism, as lipid content was increased (P < 0.05) in D7 blastocysts in treated groups (Control: 52.7 ± 3.1a, D4: 65.9 ± 2.6b, D6: 78.1 ± 2.7b). However, no effect was present for cleavage, blastocyst and cryosurvival rates. No difference was detected in mean cell number comparing the three groups (Control: 78.9 ± 9.6, D4: 82.6 ± 16.5, D6: 68.3 ± 7.8), but apoptosis rate was increased (P < 0.05) in vitrified-warmed blastocysts from treated groups (Control: 14.77*, D4: 22.28, D6: 22.22). We concluded that the combined use of lipid modulators was efficient to promote changes in lipid content of oocytes and embryos in bovine, but those changes did not reflect positively on embryo development or cryosurvival.

In Vitro Production of Embryos from Prepubertal Holstein Cattle and Mediterranean Water Buffalo: Problems, Progress and Potential

Laparoscopic ovum pick-up (LOPU) coupled with in vitro embryo production (IVEP) in prepubertal cattle and buffalo accelerates genetic gain. This article reviews LOPU-IVEP technology in prepubertal Holstein Cattle and Mediterranean Water Buffalo. The recent expansion of genomic-assisted selection has renewed interest and demand for prepubertal LOPU-IVEP schemes; however, low blastocyst development rates has constrained its widespread implementation. Here, we present an overview of the current state of the technology, limitations that persist and suggest possible solutions to improve its efficiency, with a focus on gonadotropin stimulations strategies to prime oocytes prior to follicular aspiration, and IVEP procedures promoting growth factor metabolism and limiting oxidative and endoplasmic reticulum stress.

The role of L-carnitine in bovine embryo metabolism. A review of the effect of supplementation with a metabolic modulator on in vitro embryo production

Early embryo development is driven first by the maternal RNAs and proteins accumulated during the oocyte's cytoplasmic maturation and then after the embryo genome activation. In mammalian cells, ATP generation occurs via oxidative pathways or by glycolysis, whereas in embryonic stem cells, the consumption of glucose, pyruvate, lipids, and amino acids results in ATP synthesis. Although the bovine embryo has energy reserves in glycogen and lipids, the glycogen concentration is deficient. Conversely, lipids represent the most abundant energy reservoir of bovine embryos, where lipid droplets-containing triacylglycerols are the main fatty acid stores. Oocytes of many mammalian species contain comparatively high amounts of lipids stored as droplets in the ooplasm. L-carnitine has been described as a cofactor that facilitates the mobilization of fatty acids present in the oocyte's cytoplasm into the mitochondria to facilitate β-oxidation processes. However, the L-carnitine effects by addition to media in the in vitro produced embryos on the quality are highly disputed and contradictory by different researchers. This review's objective was to explore the effect that the addition of L-carnitine on culture media could have on the overall bovine embryo production in vitro, from the oocyte metabolism to the modulation of gene expression in the developing embryos.

Lipid Metabolism in Bovine Oocytes and Early Embryos under In Vivo, In Vitro, and Stress Conditions

Lipids are a potential reservoir of energy for initial embryonic development before activation of the embryonic genome and are involved in plasma membrane biosynthesis. Excessive lipid droplet formation is detrimental to cryotolerance and is related to alterations in mitochondrial function, which likely affects lipid metabolism. Increased lipid accumulation in in vitro produced embryos is a consequence of the stress during in vitro embryonic development process. There are several open questions concerning embryo lipid metabolism and developmental potential. Oocyte maturation and embryo development in vivo and in vitro may vary if the donors are subjected to any type of stress before follicle puncture because crucial changes in oocyte/embryonic metabolism occur in response to stress. However, little is known about lipid metabolism under additional stress (such as heat stress). Therefore, in this review, we aimed to update the information regarding the energy metabolism of oocytes and early bovine embryos exhibiting developmental competence, focusing on lipid metabolic pathways observed under in vivo, in vitro, and stress conditions.

Improved cryopreservation of in vitro produced bovine embryos using FGF2, LIF, and IGF1

In vitro embryo production systems are limited by their inability to consistently produce embryos with the competency to develop to the blastocyst stage, survive cryopreservation, and establish a pregnancy. Previous work identified a combination of three cytokines [fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), and insulin-like growth factor 1 (IGF1)], called FLI, that we hypothesize improve preimplantation development of bovine embryos in vitro. To test this hypothesis, FLI was supplemented into oocyte maturation or embryo culture medium. Embryos were produced in vitro using abattoir-derived oocytes and fertilized with sperm from a single bull known to have high fertility. After an 18-20 h fertilization period, putative zygotes were cultured in synthetic oviductal fluid (SOF) for 8 days. The addition of FLI to the oocyte maturation medium increased (P < 0.05) the dissociation of transzonal projections at 12, 18, and 24 h of maturation, as well as, the proportion of oocytes that reached the metaphase II stage of meiosis. Additionally, lipid content was decreased (P < 0.05) in the blastocyst stage embryo. The addition of FLI during the culture period increased development to the blastocyst stage, cytoskeleton integrity, and survival following slow freezing, as well as, decreased post thaw cell apoptosis (P < 0.05). In conclusion, the supplementation of these cytokines in vitro has the potential to alleviate some of the challenges associated with the cryo-survival of in vitro produced bovine embryos through improving embryo development and embryo quality.

Influence of l-carnitine on lipid metabolism of buffalo cumulus-oocyte complexes matured in either fetal bovine serum or fatty acid-free bovine serum albumin

Consequences of oocyte supplementation with l-carnitine may vary depending on species-specific cellular lipid profile, level of mitochondrial activity, or even on ipid availability in culture medium. This study aimed to evaluate l-carnitine supplementation on competence and gene expression of enzymes related to lipid metabolism in oocytes and cumulus cells from buffalo COCs matured in the presence or absence of fetal bovine serum (FBS). COCs were matured in vitro in FBS (10%) or bovine serum albumin fatty acid-free (BSA-FAF) (0.4%) and with or without supplementation with l-carnitine (3.03 mM). COCs matured in the presence of FBS or BSA-FAF were fertilized and cultured, then supplemented with l-carnitine during in vitro maturation or in vitro embryo culture. Finally, in vivo mature and immature COCs were included for gene expression analysis. COCs matured in culture medium with FBS in the presence of l-carnitine produced a lower blastocyst rate (p ≤ 0.05) compared to controls. In turn, the blastocyst rate from COCs matured with BSA-FAF in the presence of l-carnitine was similar to controls (p > 0.05), and higher than FBS + L-carnitine treated COCs (p ≤ 0.05). Addition of l-carnitine during embryo culture showed no differences in blastocyst production between experimental groups and controls (p > 0.05). In cumulus cells, gene expression of ACACA, SCD and FASN was upregulated in COCs matured in the presence of BSA-FAF + L-carnitine, while all genes in oocytes were significantly expressed upregulated by COCs matured in vivo, and only BSA-FAF + L-carnitine group showed similar expression of the FASN gene. In conclusion, the consequences of l-carnitine supplementation during in vitro maturation of buffalo COCs on oocyte competence vary depending on presence or absence of FBS in culture. With FBS, l-carnitine impairs oocyte competence, while in its absence, gene expression suggests adequate lipid metabolism and increased oocyte competence.

l-Carnitine Supplementation during In Vitro Maturation and In Vitro Culture Does not Affect the Survival Rates after Vitrification and Warming but Alters Inf-T and ptgs2 Gene Expression

l-carnitine is a potent antioxidant used for in vitro culture systems. Controversial results have been reported using l-carnitine in culture medium at different stages of in vitro bovine embryo production. Cumulus-oocyte complexes (n = 843) were in vitro-fertilized and cultured and added (treatment group) or not added (control group) with l-carnitine. At day three of culture, each group was subdivided into two subgroups receiving no l-carnitine (group 1), 3.8 mM l-carnitine added during in vitro maturation (group 2), 1.5 mM added during the in vitro culture (group 3), and 3.8 mM and 1.5 mM added during the maturation and culture, respectively (group 4). At day 8, blastocyst embryos were examined for mitochondrial activity, the presence of lipid droplets, total cell number, gene expression, and cryotolerance by vitrification. The data were analyzed with a one-way analysis of variance. l-carnitine added in the late in vitro culture significantly reduced mitochondrial activity and lipid content, and upregulated ifn-τ and ptgs2 gene expression compared to controls (p < 0.05). l-carnitine supplementation did not significantly affect the embryo rate production or survival rate after vitrification and warming (p > 0.05). l-carnitine supplementation significantly improved embryo potential to develop viable pregnancies in agreement with a study reporting improved pregnancy rates.

Production of in vitro bovine embryos supplemented with l-carnitine in different oxygen tensions and the relation to nitric oxide

The aim of this study was to evaluate the production of bovine embryos in vitro when supplemented with l-carnitine for 24 h beginning on day 5 (d 5) under two different oxygen tensions (20% or 5%) and the relationship of nitric oxide (NO) in in vitro culture (IVC) medium to embryo development. Cumulus–oocyte complexes (COC; n = 837) were matured in vitro for 24 h and fertilization was performed for 18 h. Zygotes were cultured in vitro for 9 days after in vitro fertilization in synthetic oviductal fluid (SOF) medium with 5% fetal calf serum. At d 5 the plates were assigned to one of four treatment groups: high (20%) or low (5%) O2 tension either with or without the addition of 3.03 mM l-carnitine (High-Cont, High-Lcar, Low-Cont, Low-Lcar). The concentration of NO in the culture medium was evaluated on d 5, d 6 and d 9. On d 7, parts of the embryos were submitted for evaluation of intracellular lipid droplets. The cleavage rate was similar (P > 0.05) between high and low O2 tension and the blastocyst rate was similar in all conditions evaluated. The hatching rate was higher (P < 0.05) for Low-Cont. The NO concentration was higher at d 9 under low O2 tension (P < 0.1). The addition of 3.03 mM l-carnitine between d 5 and d 6 of IVC was not efficient in reducing cytoplasmic lipid content of bovine embryos. Additionally, IVC at a low oxygen tension without l-carnitine promoted better conditions for embryo development. A higher concentration of NO in medium was observed under low O2 tension.

L-carnitine supplementation in culture media improves the pregnancy rate of in vitro produced embryos with sexed semen from Bos taurus indicus cows

The in vitro embryo production industry in the actual world presents some difficulties related to low embryonic production rates, a problem that could be associated with in vitro culture conditions that differed from the in vivo (oviductal) conditions, mainly related to cytoplasmic lipid accumulation. L-carnitine is known as a modulator of β-oxidation in the developing embryo, as it has been demonstrated that it improves embryo quality without affecting the in vitro embryo production rate. The aim of the present work was to evaluate the effect of L-carnitine supplemented during the in vitro maturation and culture processes on the implantation rate of in vitro produced embryos. Supplementation with 3.8 mM of L-carnitine was used during in vitro maturation, and later, during late in vitro culture, it was added at 1.5 mM. A control group contained no L-carnitine supplementation. Bovine oocytes obtained by ultrasound-guided follicle aspiration from healthy Bos taurus indicus cows were matured, fertilized and cultured in vitro. Multiparous F1 (Bos taurus taurus × Bos taurus indicus) cows were used as recipients. Overall, 460 oocytes were processed in three independent replicates from in vitro maturation until day 8 of the in vitro culture. No significant difference was found between treatments of in vitro embryo production. However, pregnancy rate at days 45 and 72 was significantly higher in blastocysts derived from L-carnitine treatment (31.55 ± 9.78%) compared to the control group (18.68 ± 6.31%). In conclusion, addition of L-carnitine at 3.8 mM and 1.5 mM in the maturation, and culture medium after day 3 of in vitro production process, significantly improved pregnancy rate after embryo transfer.

Determinants of survival of the bovine blastocyst to cryopreservation stress: treatment with colony stimulating factor 2 during the morula-to-blastocyst transition and embryo sex

BACKGROUND

Colony-stimulating factor 2 (CSF2) is an important maternal regulator of embryonic development. Earlier research indicates that CSF2 can regulate genes involved in cellular stress responses and block apoptosis. Here, we tested whether addition of 10 ng/mL CSF2 at day 5 of development would increase the survival of blastocysts harvested at day 7 and subjected to vitrification. Additional objectives were to determine whether embryo sex affected survival or whether effects of CSF2 interacted with sex.

RESULTS

Survival after vitrification was measured as the percent of warmed blastocysts that re-established a blastocoele after culture and that underwent hatching from the zona pellucida. In the first experiment, blastocysts were vitrified, warmed, cultured for 24 h, and DNA embryo sexing performed by PCR. There was no effect of CSF2, sex, or the interaction on the percent of blastocysts that re-expanded or that were hatching or hatched. In the second experiment, vitrified blastocysts were warmed and cultured for 24, 48, and 72 h. Treatment with CSF2 increased (P = 0.021) the percent of blastocysts that re-expanded as compared to the vehicle group (overall, 77.8 ± 4.7% vs 73.3 ± 4.7%). Percent re-expansion was highest at 24 h and declined slightly thereafter (P = 0.024). Although the interaction was not significant, the effect of CSF2 was greater at 48 and 72 h than at 24 h because CSF2 reduced the incidence of embryos collapsing after re-expansion. Furthermore, the proportion of re-expanded blastocysts at 24 h that experienced blastocoel collapse by 72 h was lower (P = 0.053) for CSF2 (3.6%; 7/195) than for vehicle (8.2%; 16/195). The percent of warmed blastocysts that were hatching or hatched increased with time (P < 0.0001) but there was no effect of CSF2 or the interaction with time on hatching.

CONCLUSION

Treatment with CSF2 from day 5 to 7 of development did not cause a significant effect on the percent of blastocysts that re-established the blastocoele after 24 h of culture but CSF2 reduced the collapse of the blastocoele that occurred for a portion of the embryos that had experienced re-expansion at 24 h. Thus, CSF2 can provide protection to a proportion of blastocysts from cryodamage caused by vitrification. Further work is needed to evaluate whether CSF2 increases survival of vitrified blastocysts after embryo transfer.

Effect of L-carnitine on sperm quality during liquid storage of boar semen

Objective

This study was conducted to investigate the effect of L-carnitine on the pig semen characteristics during storage.

Methods

Spermatozoa samples were examined for spermatozoa quality and then randomly divided into 5 groups: 0 (control), 12.5, 25, 50, and 100 mM L-carnitine. Sperm motility, plasma membrane integrity and antioxidant parameters (total reactive oxygen species, total antioxidant capacity, and malondialdehyde) were evaluated after 0, 3, 5, and 10 day cooled-storage at 17°C. Moreover, ATP content, mitochondria activity as well as sperm-binding and in vitro fertilizing ability of preserved boar sperm were also investigated.

Results

Supplementation with 50 mM L-carnitine could effectively maintain boar sperm quality parameters such as sperm motility and membrane integrity. Besides, we found that L-carnitine had positive effects on boar sperm quality mainly through improving antioxidant capacities and enhancing ATP content and mitochondria activity. Interestingly, by assessing the effect of L-carnitine on sperm fertility and developmental potential, we discovered that the extender containing L-carnitine could improve sperm quality and increase the number of sperms bounding to zona pellucida, without improving in vitro fertility and development potential.

Conclusion

These findings suggested that the proper addition of L-carnitine to the semen extender improved boar sperm quality during liquid storage at 17°C.