Impact of negative energy balance and postpartum diseases during the transition period on oocyte quality and embryonic development in dairy cows

Transition period is a critical time for dairy cows because a large proportion of clinical and subclinical diseases are observed in the first month after parturition. Occurrence of negative energy balance is associated with depressed immunity and these conditions can affect oocyte quality and further embryonic development. The aim of this study was to assess the effects of negative energy balance-associated disorders on in vitro embryo production (IVP) in dairy cattle. We hypothesized that subclinical metabolic and/or inflammatory disorders have a negative effect on oocyte developmental competence and morphokinetic parameters of the resulting embryos. The study was conducted on 30 lactating Holstein-Friesian cows which were assigned into four groups: healthy (HEAL, n = 6), metabolic disease (META, n = 8), inflammatory disease (INFL, n = 8), or combined metabolic and inflammatory disease (COMB, n = 8). Ovum pick-up (OPU) was performed twice weekly on all cows over a period of four weeks (n = 8 OPU sessions/cow) starting on the fifth week postpartum, and the collected oocytes were subjected to routine IVP. Donor's health status did not affect the number of oocytes/OPU or the recovery rate (p > 0.05). The number of quality 1 oocytes collected from INFL and COMB cows was lower compared to HEAL cows (p < 0.05). Also, the percentage of quality 1 embryos was reduced in META and COMB compared to HEAL cows (p < 0.05). Cleavage, blastocyst and hatching rates were similar among groups (p > 0.05). Presence of disease did not affect the time required by zygotes to reach specific developmental stages, as recorded by means of time-lapse monitoring. Nevertheless, there was a higher probability of direct cleavage after IVF in oocytes of COMB cows compared to those of HEAL cows (p < 0.05). In conclusion, oocytes and embryos derived from dairy cows diagnosed with subclinical metabolic and/or inflammatory diseases during the transition period showed reduced quality but similar developmental potential and morphokinetics when compared to healthy cows. These results shed light on the consequences of subclinical disease on embryonic development in dairy cows which might be important for embryo transfer programs.

Cystic endometrial hyperplasia-pyometra syndrome impairs the preantral follicle reserve in domestic bitches (Canis familiaris)

Cystic endometrial hyperplasia (CEH)-pyometra syndrome is the most common uterine pathological condition reported in breeding bitches, however, their described effects on fertility are limited to uterine disorders and conception rates. As the preantral follicle population represents the available reserve of gametes recruited during the lifespan, the aim of this study was to evaluate the effects of CEH-pyometra syndrome on the: (i) preantral follicle morphology, (ii) developing follicle rates, and (iii) preantral follicle and stromal cell densities. Ovarian fragments from bitches subjected to elective or therapeutic ovariohysterectomy were allocated according to uterine diagnosis as follows: control (n = 7, clinically healthy), CEH-mucometra (n = 8, uterine lumen filled with a sterile mucus), and pyometra (n = 17, presence of a purulent mucus) groups. Overall, the control group had 3.4 and 4.1-fold higher probability (P < 0.0001) of the presence of normal preantral follicles compared with CEH-mucometra and pyometra groups, respectively. Moreover, ovarian fragments from the pyometra group showed an increase in the percentage of developing follicles (P < 0.05) compared to the control. Both CEH-mucometra and pyometra groups showed lower (P < 0.05) preantral follicle and stromal cell densities (P < 0.05) compared to the control. In summary, the CEH-pyometra syndrome decreased the percentage of morphologically normal follicles and enhanced the developing follicle rates. Additionally, a reduction of preantral follicle and stromal cell densities suggests that the inappropriate uterine environment induced by CEH-pyometra syndrome can lead to premature depletion of ovarian reserve.

Mastitis causes negative reproduction performance similar to genital diseases

The economic efficiency of dairy farms is directly influenced by reproductive performance. Reproductive performance is affected by postpartum health; however, it is unknown which diseases reduce reproductive performance or how often these diseases occur in tie-stall dairy farms. In this study, the 15 most frequent diseases in tie-stalls and their impact on reproduction were determined by logistic analysis. Data from reproductive and veterinary records of 814 cows (473 Holstein) calving between April 2016 and March 2018 reared in 9 tie-stall commercial dairy farms were used. The 15 most frequent diseases were identified by medical records. The odds ratio (OR) of the diseases reducing reproductive performance (days open, number of artificial insemination, and first artificial insemination days in milk) was measured by logistic regression analysis. We focused on mastitis, and factors (inflammation grade, causative bacteria) having a negative effect on reproduction were measured similarly. Of the 15 most frequent diseases, endometritis (OR: 5.45, p < 0.001), ovarian quiescence (OR: 3.95, p < 0.001), mastitis (OR: 2.49, p < 0.001), and follicular cyst (OR: 2.33, p = 0.006) significantly prolonged days open after adjusting for environmental factors (farm, parity, and calving season). Focusing on mastitis, mastitis with mild inflammation significantly prolonged days open. Mastitis and genital diseases were frequent diseases that reduced reproductive performance. Strategies to reduce the incidence of these diseases are considered effective for the economics of tie-stall dairy farms.

Sanguinarine Enhances the Integrity of the Blood-Milk Barrier and Inhibits Oxidative Stress in Lipopolysaccharide-Stimulated Mastitis

Mastitis is a common clinical disease which threatens the welfare and health of dairy cows and causes huge economic losses. Sanguinarine (SG) is a plant-derived alkaloid which has many biological functions, including antibacterial and antioxidant properties. The present study attempted to evaluate the effect of SG on lipopolysaccharide (LPS)-induced oxidative stress reactions and explore its potential mechanisms. The expression profile of SG was analyzed by network pharmacology, and it was found that differentially expressed genes were mainly involved in the Wnt signaling pathway and oxidative stress through GO and KEGG enrichment. In in vitro experiments, the dosage of SG was non-toxic to mouse mammary epithelial cells (mMECs) (p > 0.05). SG not only inhibited the increase in ROS induced by LPS, but also enhanced the activity of antioxidant enzymes (p < 0.05). Moreover, the results of the in vivo experiments showed that SG alleviated LPS-induced inflammatory damage of mouse mammary glands and enhanced the integrity of the blood-milk barrier (p < 0.05). Further studies suggested that SG promoted Nrf2 expression and suppressed the activation of the Wnt signaling pathway (p < 0.05). Conclusively, this study clarified the protective effect of SG on mastitis and provided evidence for new potential mechanisms. SG exerted its antioxidant function through activating Nrf2 and inhibiting the Wnt/β-catenin pathway, repairing the blood-milk barrier.

Invited review: The influence of immune activation on transition cow health and performance-A critical evaluation of traditional dogmas

The progression from gestation into lactation represents the transition period, and it is accompanied by marked physiological, metabolic, and inflammatory adjustments. The entire lactation and a cow's opportunity to have an additional lactation are heavily dependent on how successfully she adapts during the periparturient period. Additionally, a disproportionate amount of health care and culling occurs early following parturition. Thus, lactation maladaptation has been a heavily researched area of dairy science for more than 50 yr. It was traditionally thought that excessive adipose tissue mobilization in large part dictated transition period success. Further, the magnitude of hypocalcemia has also been assumed to partly control whether a cow effectively navigates the first few months of lactation. The canon became that adipose tissue released nonesterified fatty acids (NEFA) and the resulting hepatic-derived ketones coupled with hypocalcemia lead to immune suppression, which is responsible for transition disorders (e.g., mastitis, metritis, retained placenta, poor fertility). In other words, the dogma evolved that these metabolites and hypocalcemia were causal to transition cow problems and that large efforts should be enlisted to prevent increased NEFA, hyperketonemia, and subclinical hypocalcemia. However, despite intensive academic and industry focus, the periparturient period remains a large hurdle to animal welfare, farm profitability, and dairy sustainability. Thus, it stands to reason that there are alternative explanations to periparturient failures. Recently, it has become firmly established that immune activation and the ipso facto inflammatory response are a normal component of transition cow biology. The origin of immune activation likely stems from the mammary gland, tissue trauma during parturition, and the gastrointestinal tract. If inflammation becomes pathological, it reduces feed intake and causes hypocalcemia. Our tenet is that immune system utilization of glucose and its induction of hypophagia are responsible for the extensive increase in NEFA and ketones, and this explains why they (and the severity of hypocalcemia) are correlated with poor health, production, and reproduction outcomes. In this review, we argue that changes in circulating NEFA, ketones, and calcium are simply reflective of either (1) normal homeorhetic adjustments that healthy, high-producing cows use to prioritize milk synthesis or (2) the consequence of immune activation and its sequelae.

Mechanisms by which mastitis affects reproduction in dairy cow: A review

Reproductive performance is a key factor in determining the profitability of dairy farm, which is affected by many factors such as environment and diseases. Mastitis is a common and important disease, which has caused huge economic losses to the dairy industries worldwide. Mammary gland infection causes immune responses, resulting in the abnormal secretion of cytokines and hormones and abnormal function of the reproductive system such as the ovary, corpus luteum, uterus and embryo. Cows with mastitis have delayed oestrus, decreased pregnancy rate and increased risk of abortion. The adverse effects of mastitis on reproductive performance are affected by many factors, such as occurrence time, pathogen and cow factors. This paper primarily reviews the progress in the effects and mechanisms of mastitis on reproductive performance, with emphasis on maternal transcriptome, genomic analysis, epigenetic modification, microbiota, inflammatory regulation and immune evasion mechanism of mastitis, aiming to provide directions for the prevention and control of mastitis in the future.

Effects of Pre-ovulatory Follicular Fluid of Repeat Breeder Dairy Cows on Bovine Fertility Transcriptomic Markers and Oocytes Maturation and Fertilization Capacity

The current study aimed to determine the effects of the preovulatory follicular fluid (FF) of normal heifer (NH) and repeat breeder cows with subclinical endometritis (SCE) or without (nSCE) on oocyte maturation (Experiment 1) and fertilization rates (Experiment 2). Moreover, the pattern of gene expression of cumulus oocyte-complexes was evaluated in Experiment 1. In Experiment 1, nuclear maturation in the nSCE group was higher, compared to that in the SCE group (P = 0.05). In addition, the oocyte nuclear maturation in the normal heifer was significantly higher, in comparison to that of SCE groups (P < 0.05). Furthermore, the mean percentage of normal oocyte fertilization was higher in the nSCE group, compared to that in the SCE group (P < 0.05). The expressions of growth differentiation factor, GDF9; steroidogenic acute regulatory, StAR and follicle-stimulating hormone receptor, FSHr in the NH group were significantly higher, compared to those in SCE and nSCE groups (P < 0.05). Moreover, the expressions of all genes in the nSCE group were not significant, in comparison to those in the SCE group (P > 0.05). The supplementation of oocyte maturation medium with FF from pre-ovulatory follicles of repeat breeder cows resulted in less oocyte maturation and cumulus cell expansion. In conclusion, the lower fertility in RB cows could be ascribed to the lower oocyte maturation rate and less expression of GDF9, StAR, and FSHr in the cumulus-oocyte complexes.

Glutathione ethyl ester improved the age-induced decline in the developmental competence of bovine oocytes

The aberrant redox regulation and anti-oxidative defense is one of the main causes of age-induced decline in oocytes quality and embryo development in mammals. The present study aimed to elucidate the effect of glutathione ethyl ester (GSH-OEt), a cell-permeable glutathione (GSH) donor, on the developmental competence of oocytes in cows with advanced reproductive age. Oocytes were collected from cows aged 30-50 months or >120 months, which were defined as young or aged, respectively, and subjected to in vitro maturation (IVM) in the presence of 5 mM of GSH-OEt. In aged cows, the GSH level in follicular fluid was lower, and the intracellular levels of reactive oxygen species (ROS) in post-IVM oocytes was higher than those in young cows. GSH-OEt supplementation during IVM reduced the ROS contents of oocyte in aged cows but not in young cows. GSH-OEt treatment promoted the meiotic progression and increased the proportion of oocytes with mature cytoplasm containing evenly dispersed cortical granules in aged cows. After in vitro fertilization, the normal fertilization and development to the blastocyst stage were enhanced by GSH-OEt in aged cows to levels comparable to those in young cows. Further, oocyte maturation in the presence of GSH-OEt increased the proportion of diploid blastocyst in aged cows. In contrast, GSH-OEt failed to enhance the oocyte maturation, fertilization, and embryo development in young cows. Taken together, the exogenous supplementation of GSH-OEt during IVM modulated the age-related oxidative damage of bovine oocytes and improved the developmental competence of oocytes in aged cows. Oocytes presented a distinct response to GSH-OEt treatment depending on the donor age. GSH-OEt supplementation during IVM could be of practical value through the efficiency improvement of chromosomally normal embryo production in aged cows.

Effect of rosiglitazone on developmental competence of mouse embryos treated with lipopolysaccharide

Lipopolysaccharide (LPS) significantly reduces pre- and post-implantation developmental competence of embryos. One of the reason of this effect could be a consequence of TLR4-mediated inflammation. In this study, we assessed the anti-inflammatory effect of peroxisome proliferator activated receptor γ (PPAR γ) agonist, rosiglitazone (RGZ), in LPS-treated mouse embryos. Initially, the optimal doses of LPS, RGZ and GW9662 (a potent and selective PPARγ antagonist) were determined by treating the mouse zygotes up to blastocyst stage and assessment of compaction and blastocyst rates. Quantitative PCR was used to assess the mRNA expression of inflammatory cytokines. Immunostaining was used to study the translocation of PPARγ in blastocysts. Finally, the blastocysts were transferred to surrogate mouse to determine the post-implantation developmental competence. 0.0625 mg/mL of LPS significantly reduced the developmental competency by around 50% compared to control group. 10 μM of RGZ significantly ameliorated the toxic effect of LPS, which was also significantly reversed by 1.25 μM GW9662. Through immunostaining, it was shown that LPS could prevent the translocation of PPARγ to nucleus; and translocation was facilitated by RGZ and this effect was reversed by GW9662. A similar effect was also observed for the mRNA expression of inflammatory cytokines (Il-1β and Il-6). LPS significantly increased the expression of these cytokines, while RGZ significantly reduced their expression, which was also significantly reversed by GW9662. It was also shown that embryos exposed to LPS had significantly reduced post implantation developmental competence which was considerably improved by treatment with RGZ. In conclusion, these data may have clinical implications for ameliorating the adverse effects of LPS in dairy farming and infertility treatment.

Inflammatory diseases in dairy cows: Risk factors and associations with pregnancy after embryo transfer

The objectives of the present prospective cohort study were to identify risk factors for inflammatory diseases in Holstein-Gyr crossbred dairy cows and characterize the associations of those diseases with pregnancy per embryo transfer (ET). Diseases were diagnosed in the first 60 d postpartum in 252 primiparous and 481 multiparous cows. Uterine diseases (UTD) included retained placenta, metritis, clinical endometritis, and subclinical endometritis. Nonuterine diseases (NUTD) included mastitis, lameness, pneumonia, and displaced abomasum. Blood was sampled on d 0, 1, and 2 postpartum and analyzed for concentrations of haptoglobin, fatty acids, total Ca (tCa), P, and Mg, and again on d 8 postpartum and analyzed for concentration of β-hydroxybutyrate. The association between concentrations of metabolites in serum and inflammatory diseases was determined. Cows received a timed ET program starting 28 ± 3 d postpartum with first ET at 46 ± 3 d postpartum using fresh in vitro-produced embryos. Pregnancy was diagnosed on d 31 and 59 of presumptive gestation. Overall, 63.3% of the cows were diagnosed with UTD and 20.6% with NUTD. The risk factors for UTD included season of calving, parity group, calving problems, days with subclinical hypocalcemia, and serum concentrations of haptoglobin and Mg, whereas the risk factors for NUTD were parity group and serum Mg concentration. Cows that developed UTD had increased concentrations of haptoglobin on d 2 and fatty acids on d 1 and 2, and reduced concentrations of tCa on d 1 and 2 and of P and Mg on d 2 postpartum compared with cows without UTD. Cows that developed NUTD had increased concentrations of fatty acids on d 0 to 2 postpartum, and decreased concentrations of tCa and P on d 0 and 1, and of Mg on d 1 and 2 postpartum compared with cows without NUTD. Cows that developed NUTD had a 340-kg reduction in milk yield in the first 60 d postpartum. Inflammatory diseases were associated with lesser body condition score and increased loss of body condition in the first 70 d postpartum. Maintenance of pregnancy after ET was reduced in UTD cows following the first (41.7 vs. 25.4%) or all ET (46.4 vs. 36.2%), whereas maintenance of pregnancy was reduced in NUTD cows only at the second ET (39.0 vs 25.9%). The reduced pregnancy maintenance in UTD cows combined with a reduced 21-d service rate (61.9 vs. 54.8%) decreased the 21-d cycle pregnancy rate (28.6 vs. 19.9%) and the hazard of pregnancy to 300 d postpartum by 35%, resulting in an extra 32 d open. In conclusion, inflammatory diseases depressed fertility in dairy cows receiving ET, with the greatest impact observed in UTD cows. This suggests that local inflammation of the uterus impairs maintenance of pregnancy in dairy cows following ET.

Melatonin slightly alleviates the effect of heat shock on bovine oocytes and resulting blastocysts

Heat stress is associated with increased production of reactive oxygen species (ROS) and disruption of bovine oocyte function. Here, we examined whether the antioxidant melatonin can alleviate the deleterious effects of heat stress on oocyte developmental competence. Cumulus-oocyte complexes were matured for 22 h at 38.5 °C (control) or for 22 h at 41.5 °C (heat shock) with or without 1.0 × 10^-7 M melatonin. At the end of maturation, a subgroup of oocytes was examined for nuclear and cytoplasmic maturation, ROS level and mitochondrial membrane potential. A second subgroup of oocytes underwent fertilization (18 h), and putative zygotes were cultured in an incubator equipped with a time-lapse system for ∼190 h. Cleavage rate and the proportion of blastocysts, as well as embryo kinetics were recorded. Expanded blastocysts were collected and their transcript abundance was evaluated. Heat shock increased ROS and reduced the proportion of oocytes that resumed meiosis and reached the metaphase-II stage. Exposing oocytes to heat shock with melatonin alleviated these effects to some extent, expressed by a marginal reduction in ROS level and increased proportion of metaphase-II stage oocytes. Neither the distribution of oocyte cortical granules nor polarization of the mitochondrial membrane differed between control and heat-shocked oocytes cultured with or without melatonin. Heat shock reduced the proportion of embryos that cleaved and developed to blastocysts, characterized by alterations in kinetics of the developed embryos expressed by a delay in the first cleavage, second cleavage and blastocyst formation for heat-shock vs. control groups. Melatonin did not restore the competence or kinetics of embryos developed from heat-shocked oocytes. However, expanded blastocysts developed from heat-shocked oocytes treated with melatonin expressed a higher transcript abundance of genes associated with mitochondrial function, relative to the control and heat-shock group. In summary, melatonin improved the oxidative status of heat-shocked oocytes to some extent and had a beneficial effect on maternal mitochondrial transcripts in the developed blastocysts.

Uterine infusion of bacteria alters the transcriptome of bovine oocytes

Postpartum uterine infection reduces fertility in dairy cattle; however, the mechanisms of uterine infection-mediated infertility are unknown. Paradoxically, infection-induced infertility persists after the resolution of disease. Oocytes are a finite resource, which are present at various stages of development during uterine infection. It is likely that oocyte development is influenced by uterine infection-induced changes to the follicular microenvironment. To better understand the impact of infection on oocyte quality we employed global transcriptomics of oocytes collected from heifers after receiving intrauterine infusion of pathogenic Escherichia coli and Trueperella pyogenes. We hypothesized that the oocyte transcriptome would be altered in response to intrauterine infection. A total of 452 differentially expressed genes were identified in oocytes collected from heifers 4 days after bacteria infusion compared to vehicle infusion, while 539 differentially expressed genes were identified in oocytes collected from heifers 60 days after bacteria infusion. Only 42 genes were differentially expressed in bacteria-infused heifers at both Day 4 and Day 60. Interferon, HMGB1, ILK, IL-6, and TGF-beta signaling pathways were downregulated in oocytes collected at Day 4 from bacteria-infused heifers, while interferon, ILK, and IL-6 signaling were upregulated in oocytes collected at Day 60 from bacteria-infused heifers. These data suggest that bacterial infusion alters the oocyte transcriptome differently at Day 4 and Day 60, suggesting different follicle stages are susceptible to damage. Characterizing the long-term impacts of uterine infection on the oocyte transcriptome aids in our understanding of how infection causes infertility in dairy cattle.

Differences in virulence between the two more prevalent Staphylococcus aureus clonal complexes in rabbitries (CC121 and CC96) using an experimental model of mammary gland infection

Staphylococcal mastitis is a major health problem in humans and livestock that leads to economic loss running in millions. This process is currently one of the main reasons for culling adult rabbit does. Surprisingly, the two most prevalent S. aureus lineages isolated from non-differentiable natural clinical mastitis in rabbits (ST121 and ST96) generate different immune responses. This study aimed to genetically compare both types of strains to search for possible dissimilarities to explain differences in immune response, and to check whether they showed similar virulence in in vitro tests as in experimental intramammary in vivo infection. The main differences were observed in the enterotoxin gene cluster (egc) and the immune-evasion-cluster (IEC) genes. While isolate ST121 harboured all six egc cluster members (seg, sei, selm, seln, selo, selu), isolate ST96 lacked the egc cluster. Strain ST96 carried a phage integrase Sa3 (Sa3int), compatible with a phage integrated into the hlb gene (β-haemolysin-converting bacteriophages) with IEC type F, while isolate ST121 lacked IEC genes and the hlb gene was intact. Moreover, the in vitro tests confirmed a different virulence capacity between strains as ST121 showed greater cytotoxicity for erythrocytes, polymorphonuclear leukocytes and macrophages than strain ST96. Differences were also found 7 days after experimental intramammary infection with 100 colony-forming units. The animals inoculated with strain ST121 developed more severe gross and histological mastitis, higher counts of macrophages in tissue and of all the cell populations in peripheral blood, and a significantly larger total number of bacteria than those infected by strain ST96.

Detection of bacteria in bovine ovarian follicular fluid

The aim of this study was to examine the sterility of follicular fluid in large ovarian follicles in dairy cows. In all, 17 samples of paired follicular fluids and uterine contents collected from post-slaughtered dairy cows were cultured to detect aerobic and facultative anaerobic bacteria. Furthermore, the origin of the bacterial isolates from samples of follicular fluid and the uteri was also investigated using PFGE analysis. Follicular fluid concentrations of lipopolysaccharides were also determined. Of 17 uterine samples, 15 (88%) were detected as contaminated. In total, nine different bacterial genera and species were identified in the uterine and follicular fluid samples. Escherichia coli was the most prevalent bacterial species isolated from the uterine samples. Out of seven isolates of Staphylococcus aureus from the uterine samples, 6 (85%) were coagulase positive. Six isolates of Staphylococcus spp. were identified in 6 out of 17 follicular fluid samples (35%). Two out of six isolates were identified as Staphylococcus aureus (33%). Our results show that ovarian follicular fluid is not sterile in the bovine. The presence of Staphylococcus aureus in follicular fluid may partly explain the occurrence of infertility in some dairy cows. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the present study show that ovarian follicular fluid is not sterile in bovines. The presence of Staphylococcus aureus in follicular fluid may partly explain the occurrence of infertility in some dairy cows.

Oocyte maturation in plasma or follicular fluid obtained from lipopolysaccharide-treated cows disrupts its developmental competence

Mastitis has deleterious effects on ovarian function and reproductive performance. We studied the association between plasma or follicular fluid (FF) obtained from endotoxin-induced mastitic cows, and oocyte developmental competence. Lactating Holstein cows were synchronized using the Ovsynch protocol. On Day 6 of the synchronized cycle, an additional PGF_2α dose was administered, and either Escherichia coli endotoxin (LPS, 10 μg; n = 3 cows) or saline (n = 3 cows) was administered to one udder quarter per cow, 36 h later. Milk samples were collected and rectal temperatures recorded. Cows treated with LPS showed a typical transient increase in body temperature (40.3 °C ± 0.4), whereas cows treated with saline maintained normal body temperature (38.9 °C ± 0.04). A higher (P < 0.05) somatic cell count was recorded for cows treated with LPS. Plasma samples were collected and FF was aspirated from the preovulatory follicles by transvaginal ultrasound probe, 6 h after LPS administration. Radioimmunoassay was performed on plasma samples to determine estradiol and cortisol concentrations. Either FF or plasma was further used as maturation medium. In the first experiment, oocytes were matured in TCM-199 (Control) or in FF aspirated from cows treated with saline (FF-Saline) or LPS (FF-LPS). Cleavage rate to the 2- to 4-cell stage embryo did not differ among groups. However, the proportion of developed blastocysts on Day 7 postfertilization in the FF-LPS group tended to be lower for that in FF-Saline and was lower (P < 0.05) than that in the Control groups (10.6 vs. 22.4 and 24.4%, respectively). In the second experiment, oocytes were matured in TCM-199 (Control), or in plasma obtained from cows treated with saline (Plasma-Saline) or LPS (Plasma-LPS). Similar to the FF findings, cleavage rate did not differ among groups; however, the proportion of developing blastocysts tended to be lower in the Plasma-LPS group than in the Plasma-Saline group and was lower (P < 0.05) from that in the Control group (11.0 vs. 25.5 and 34.7%, respectively). The proportion of apoptotic cells per blastocyst, determined by TUNEL assay, did not differ among the experimental groups. The findings shed light on the mechanism by which mastitis induces a disruption in oocyte developmental competence. Further studies are required to clarify whether the negative effect on oocyte developmental competence is a result of LPS, by itself, or due to elevation of secondary inflammatory agents.

Comparing effects of bovine Streptococcus and Escherichia coli mastitis on impaired reproductive performance

In 2 epidemiological studies, we evaluated the effect of mastitis induced by gram-positive Streptococcus and gram-negative Escherichia coli on impaired reproductive performance in lactating Holstein cows. In the first study, 52,202 cows from 178 dairy farms throughout Israel were divided into groups based on infection before first artificial insemination (AI) with Streptococcus or E. coli, 3 groups with elevated somatic cell count (SCC) without infection by those pathogens [low SCC (200-400) × 10³ cell/mL; medium SCC (401-1,000) × 10³ cell/mL; high SCC, >1,000 × 10³ cell/mL], and uninfected controls. Pregnancy per first AI (P/1stAI) and pregnancy rate at 300 d in milk (PREG 300) were analyzed by the GLIMMIX procedure (SAS); number of AI per pregnancy (AI/P), days open, and rest days (calving to first AI) were analyzed by the MIXED procedure (SAS Institute Inc., Cary, NC). Values of P/1stAI were similarly low for Streptococcus and E. coli (27-28%) versus 42% in controls; PREG 300 was lower for Streptococcus (76%) than for E. coli (79%) versus 88% for uninfected controls and a mean 83% for the elevated SCC groups. Days open and number of AI/P were higher than in controls and similar in Streptococcus and E. coli groups. The second study included 778 cows on 6 dairy farms; the cows were infected before first AI by Streptococcus or E. coli or uninfected. Resumption of cyclicity was determined by an automated activity-monitoring system, and data were sorted by time of infection before or after cyclicity resumed. The Streptococcus group had lower P/1stAI before and after cyclicity (26 and 27%, respectively) than the E. coli group (31 and 34%, respectively) and uninfected controls (42%). Notably, PREG 300 in the Streptococcus group before (73%) and after (67%) cyclicity was much lower than for the E. coli group (85 and 93%, respectively) and the controls (95%). A marked rise in day of cyclicity resumption (∼80 d) was observed in cows that were infected early on. Number of AI/P was higher in the mastitic groups than in uninfected controls. Uterine disease postpartum, although more prevalent among Streptococcus cows, did not substantially alter the larger reduction in P/1stAI and PREG 300 in Streptococcus versus E. coli cows. Thus, long-term Streptococcus-induced mastitis disrupted fertility more than short-term acute E. coli-induced mastitis, resulting in a much higher percentage of Streptococcus cows in late lactation that did not conceive due to reproduction failure.

Effects of follicular fluid of preovulatory follicles of repeat breeder dairy cows with subclinical endometritis on oocyte developmental competence

The aims of the present study were to determine the concentrations of lipopolysaccharide (LPS), hormonal progesterone, estradiol-17β, insulin growth factor (IGF-1) and magnesium in the serum and the preovulatory follicle follicular fluid (FF) in repeat breeder (RB) cows without (nSCE) or with subclinical endometritis (SCE), and further to examine the effects of this FF on developmental competence of cattle oocytes. In Experiment 1, 13 of 23 clinically healthy Holstein RB cows were identified (uterine PMNs) to have SCE. The cows were estrous synchronized, and 6-12 h after detection of standing estrus, FF and blood of the preovulatory follicles were collected. The mean (±SD) LPS (862.3 ± 148.1 compared with 1063.4 ± 262.8 EU/ml, P = 0.04) and estradiol-17β (188.9 ± 15.8 compared with 162.0 ± 31.5 ng/ml, P = 0.02) concentrations of FF was different between nSCE and SCE cows. In Experiment 2, FF of RB cows with relatively lesser (nSCE, n = 4) and greater (SCE, n = 4) percentages of uterine PMNs was separately added to the oocyte maturation medium for in vitro embryo production. Addition of FF from SCE cows to the oocyte maturation medium resulted in a lesser rate of development to the blastocyst stage than that of the nSCE cows (21.9 ± 1.8 compared with 27.8 ± 2.5%, P < 0.05). Results of the present study indicate greater FF LPS concentration may result in a lesser quality microenvironment milieu for the final stages of oocyte maturation in RB dairy cows with subclinical endometritis. In addition, supplementation of oocyte maturation medium with FF of preovulatory follicles from RB cows with subclinical endometritis resulted in a lesser potential of in vitro oocyte developmental competence.

Application of intracytoplasmic sperm injection to the embryo production in aged cows

Reduction in oocyte quality is a major factor responsible for declining fertility associated with maternal aging in cows. The objective of the present study was to determine whether intracytoplasmic sperm injection (ICSI) could increase the efficiency of embryo production in older cows. We used cows aged 30 to 50 months or >120 months, which were defined as young or aged, respectively. The distribution of cortical granules in oocytes was affected by age as older cows had lower proportion of oocytes with mature cytoplasm containing evenly dispersed cortical granules compared to young cows. Although fertilization rates did not differ significantly between the two groups after in vitro fertilization (IVF), the rate of abnormal fertilization was higher, and the numbers of total and diploid blastocysts were lower for aged cows compared to young cows. However, in the embryos produced by ICSI, there was no significant difference in these parameters between young and aged cows. Although ICSI did not improve the blastocyst development rate, ICSI increased the proportion of diploid blastocysts in aged cows compared to IVF. In conclusion, maternal aging may negatively affect cytoplasmic maturation of bovine oocytes, which could be associated with abnormal fertilization or low developmental competence of oocytes. Our data also suggests beneficial effects of ICSI on the production of chromosomally normal embryos in aged cows.

Detrimental effects of lipopolysaccharides on maturation of bovine oocytes

Objective

Gram-negative bacteria lipopolysaccharide (LPS) has been reported to be associated with uterine impairment, embryonic resorption, ovarian dysfunction, and follicle retardation. Here, we aimed to investigate the toxic effects of LPS on the maturation ability and parthenogenetic developmental competence of bovine oocytes.

Methods

First, we developed an in vitro model to study the response of bovine cumulus-oocyte complexes (COCs) to LPS stress. After incubating germinal vesicle COCs in 10 μg/mL of LPS, we analyzed the following three aspects: the expression levels of the LPS receptor toll-like receptor 4 (TLR4) in COCs, activities of intracellular signaling protein p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor-kappa B (NF-κB); and the concentrations of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-6. Furthermore, we determined the effects of LPS on the maturation ability and parthenogenetic developmental competence of bovine oocytes.

Results

The results revealed that LPS treatment significantly elevated TLR4 mRNA and protein expression levels in COCs. Exposure of COCs to LPS also resulted in a marked increase in activity of the intracellular signaling protein p-p38 MAPK and NF-κB. Furthermore, oocytes cultured in maturation medium containing LPS had significantly higher concentrations of the proinflammatory cytokines IL-1β, TNF-α, and IL-6. LPS exposure significantly decreased the first polar body extrusion rate. The cytoplasmic maturation, characterized by polar body extrusion and distribution of peripheral cortical granules, was significantly impaired in LPS-treated oocytes. Moreover, LPS exposure significantly increased intracellular reactive oxygen species levels and the relative mRNA abundance of the antioxidants thioredoxin (Trx), Trx2, and peroxiredoxin 1 in oocytes. Moreover, the early apoptotic rate and the release of cytochrome C were significantly increased in response to LPS. The cleavage, morula, and blastocyst formation rates were significantly lower in parthenogenetically activated oocytes exposed to LPS, while the incidence of apoptotic nuclei in blastocysts was significantly increased.

Conclusion

Together, these results provide an underlying mechanism by which LPS impairs maturation potential in bovine oocytes.

Subclinical mastitis interferes with ovulation, oocyte and granulosa cell quality in dairy cows

The objective was to evaluate the effect of mastitis by somatic cell count (SCC) on follicular growth, ovulation, oocytes and cumulus cells quality and on the concentration and size of exosomes in follicular fluid of dairy cows. In the study, crossbred cows (Bos taurus - Holstein x Bos indicus - Gir) were classified for analysis as Control (SCC<200.000 cells/mL) and Mastitis (SCC>400.000 cells/mL) groups. In experiment 1 (follicular dynamics), cows (n = 57) were submitted to ultrasound evaluations every 24 h, from progesterone-releasing-intravaginal-device (PRID) removal (D8) until 48 h later (D10). Thereafter, evaluations were performed every 12 h, until ovulation or up to 96 h after PRID removal. In experiment 2 (oocyte, cumulus complexes, and follicular fluid evaluation), cows (n = 26) were submitted to follicular aspiration (OPU) for oocyte quality and cumulus cells transcript evaluation. The amount of cumulus complexes transcripts (BCL2, BAX, PI3K, PTEN, FOXO3) was determined by Real-Time Polymerase Chain Reaction. Moreover, seven days after the OPU session, the dominant follicle was aspirated. Exosomes were isolated from the follicular fluid for evaluation of particle size and concentration. Ovulation rate [Control 77.4% (24/31) and Mastitis 57.7% (15/26); P = 0.09] and viable oocytes rate [Control 59.1% (130/220) and Mastitis 41.9% (125/298); P = 0.01] were higher in Control animals. Additionally, there was a greater number of degenerate oocytes [Control 6.7 ± 1.2 and Mastitis 13.3 ± 5.5; (P = 0.001)] in subclinical mastitis cows. There was greater abundance (P = 0.003) of BAX cumulus cell transcripts and exosome mean (P = 0.03) and mode (P = 0.02) was smaller in subclinical mastitis cows. In conclusion, ovulation rate, oocyte quality, and exosome diameter were smaller in cows with SCC>400.000 cells/mL.

Effects of lipopolysaccharide on maturation of bovine oocyte in vitro and its possible mechanisms

Lipopolysaccharide disturbs the secretion of gonadotropin, endometrial function and implantation efficiency. However, there is little information regarding the effects of lipopolysaccharide on cyclic ovary activity, especially oocyte maturation. Therefore, we aimed to investigate the effects of lipopolysaccharide on the maturation potential of bovine oocytes. We found that lipopolysaccharide exposure significantly decreased the first polar body extrusion rate and delayed the cell cycle progression. The abnormal spindle rate was significantly increased in lipopolysaccharide treatment group, accompanied by disrupted localization and level of phosphorylated mitogen-activated protein kinase (p-MAPK). Moreover, lipopolysaccharide treatment significantly increased intracellular reactive oxygen species (ROS) levels and the early apoptotic rate in oocytes. The pro-apoptotic caspase-3 and Bax mRNA levels and caspase-3 protein level were significantly increased, whereas the anti-apoptotic Bcl-2 and XIAP transcript abundance were significantly decreased in lipopolysaccharide exposure group. Furthermore, the dimethyl-histone H3 lysine 4 (H3K4me2) level was significantly increased, while the DNA methylation (5-mC) and dimethyl-histone H3 lysine 9 (H3K9me2) levels were markedly decreased in oocytes treated with lipopolysaccharide. In conclusion, lipopolysaccharide exposure inhibits the maturation potential of bovine oocytes by affecting cell cycle, cytoskeletal dynamics, oxidative stress, and epigenetic modifications.

Milk amyloid A as a biomarker for diagnosis of subclinical mastitis in cattle

Background and Aim

Mastitis is one of the most vital noteworthy monetary risks to dairy ranchers and affects reproductive performance in dairy cattle. However, subclinical mastitis (SCM) negatively affects milk quality and quantity and associated with economic losses as clinical mastitis. It is recognizable only by additional testing. Somatic cell count (SCC) is currently used worldwide for the screening of intramammary infection (IMI) infections. However, somatic cells (SC) are affected by numerous factors and not always correlate with infection of the udder. Therefore, the aim of the present study was to evaluate the milk amyloid A (MAA) in the milk of normal and SCM cows and compare the sensitivity of both MAA secretion and SCC in response to mammary gland bacterial infection.

Materials and Methods

A total of 272 quarter milk samples collected from 68 Friesian cows after clinical examination for detection of clinical mastitis were employed in this study. All quarter milk samples (272) were subjected to bacteriological examination, while SCs were assessed in samples (220). Following SCC estimation and bacteriological examination, the apparently normal quarter milk samples were categorized into 7 groups and MAA concentration was estimated in normal and subclinical mastitic milk samples.

Results

Prevalence of clinical mastitis was 19.12 % (52 quarters), while 80.88 % (220 quarters) were clinically healthy with normal milk secretion. Of those 220 clinically healthy quarter milk samples, 72 (32.73%) showed SCM as detected by SCC (SCC ≥500,000 cells/ml). The most prevalent bacteria detected in this study were streptococci (48.53%), Staphylococcus aureus (29.41%), Escherichia coli (36.76%), and coagulase-negative staphylococci (11.76%). Results of MAA estimation revealed a strong correlation between MAA secretion level and SCC in agreement with the bacteriological examination. Interestingly, there was a prompt increase in MAA concentration in Group III (G III) (group of milk samples had SCC ≤200,000 cells/ml and bacteriologically positive) than Group I (G I) (group of milk samples with SCC ≤500,000 cells/ml and bacteriologically negative), as MAA concentration in G III was about 4 times its concentration in G I.

Conclusion

Our study provides a strong evidence for the significance of MAA measurement in milk during SCM, and MAA is more sensitive to IMI than SCC. This can be attributed to rapid and sensitive marker of inflammation. The advantage of MAA over other diagnostic markers of SCM is attributed the minute or even undetectable level of MAA in the milk of healthy animals, it is not influenced by factors other than mastitis, and could be estimated in preserved samples. Therefore, we recommend that estimation of MAA concentration in milk is a more useful diagnostic tool than SCC to detect SCM and to monitor the udder health in dairy cattle.

Human granulosa-luteal cells initiate an innate immune response to pathogen-associated molecules

The microenvironment of the ovarian follicle is key to the developmental success of the oocyte. Minor changes within the follicular microenvironment can significantly disrupt oocyte development, compromising the formation of competent embryos and reducing fertility. Previously described as a sterile environment, the ovarian follicle of women has been shown to contain colonizing bacterial strains, whereas in domestic species, pathogen-associated molecules are concentrated in the follicular fluid of animals with uterine infection. The aim of this study is to determine whether human granulosa-luteal cells mount an innate immune response to pathogen-associated molecules, potentially disrupting the microenvironment of the ovarian follicle. Human granulosa-luteal cells were collected from patients undergoing assisted reproduction. Cells were cultured in the presence of pathogen-associated molecules (LPS, FSL-1 and Pam3CSK4) for 24h. Supernatants and total RNA were collected for assessment by PCR and ELISA. Granulosa-luteal cells were shown to express the molecular machinery required to respond to a range of pathogen-associated molecules. Expression of TLR4 varied up to 15-fold between individual patients. Granulosa-luteal cells increased the expression of the inflammatory mediators IL1B, IL6 and CXCL8 in the presence of the TLR4 agonist E. coli LPS. Similarly, the TLR2/6 ligand, FSL-1, increased the expression of IL6 and CXCL8. Although no detectable changes in CYP19A1 or STAR expression were observed in granulosa-luteal cells following challenge, a significant reduction in progesterone secretion was measured after treatment with FSL-1. These findings demonstrate the ability of human granulosa-luteal cells to respond to pathogen-associated molecules and generate an innate immune response.

Inherent inferior quality of follicular fluid in repeat breeder heifers as evidenced by low rates of in vitro production of bovine embryos

The aims of the present study were to determine the effect of follicular fluid obtained from the ovulatory follicle of repeat breeder heifers on in vitro oocyte maturation (Experiment 1), fertilization (Experiment 2) and production of bovine embryos (Experiment 3). Holstein virgin heifers (VH, n = 5) with normal fertility or repeat breeder syndrome (RBH, n = 5) were used in the present study. Follicular fluid of VH and RBH was aspirated from ovulatory follicles and used as maturation medium. Bovine oocytes were aspirated from follicles of slaughterhouse ovaries and randomly allocated in three groups; in Group 1, oocytes cultured in TCM-199 supplemented with 10% heat-treated fetal calf serum and hormones (5 IU/mL hCG plus 0.1 IU/mL rFSH); in Group 2, oocytes cultured in TCM-199 supplemented with 10% filtered follicular fluid of VH without hormones; in Group 3, oocytes cultured in TCM-199 supplemented with 10% filtered follicular fluid of RBH without hormones. The mean (±SEM) percentage of matured oocytes was different between VH and RBH groups (72.2 ± 4.0 vs 56.4 ± 4.6%; P < 0.05, respectively). Further, the mean (±SEM) percentage of normal oocyte fertilization was higher in the VH than the RBH group (49.3 ± 2.1 vs 32.0 ± 4.2; P < 0.05, respectively). The mean percentage of embryos developed to the blastocyst stage was higher in the VH than the RBH group (12.0 ± 1.3 vs 7.0 ± 1.6; respectively; P < 0.05). In conclusion, our findings support our hypothesis that the ovulatory follicle microenvironment of Holstein repeat breeder heifers places their oocytes at a developmental disadvantage compared with Holstein fertile virgin heifers and that this suggest the existence of an inherent inferior quality of the ovulatory follicle microenvironment in repeat breeding Holstein heifers.

Comparing the effects of heat stress and mastitis on ovarian function in lactating cows: basic and applied aspects

Reduced reproductive performance of lactating cows is strongly associated with environmental and pathogenic stressors. This review summarizes the most recent knowledge on the effects of acute or chronic heat stress (HS) and acute or chronic intramammary infection (IMI) on ovarian function. It also offers various approaches for improving the fertility of cows under chronic HS or IMI. Comparing the 2 stressors reveals a few similarities in the mode of alteration in the hypothalamus-pituitary-ovarian axis, in particular, in the follicle and its enclosed oocyte. Both HS and IMI cause a reduction in the preovulatory LH surge, with a pronounced effect in cows with IMI, and consequently, ovulation is being delayed or inhibited. Both stresses induce changes in follicular growth dynamics, reduce follicular steroidogenesis, and disrupt follicular dominance. Unlike their effects on follicular function, the effects of mastitis and HS on corpus luteum (CL) function are debatable. Under chronic summer thermal stress, several, but not all, studies show reduced progesterone secretion by the CL. Subclinical mastitis does not affect CL function, whereas the effect of clinical mastitis is controversial; some show a reduction in progesterone, whereas others do not. Both stresses have been found to impair cytoplasmic and nuclear maturation of oocytes, associated with reduced embryonic development. These findings have provided insights into the mechanism by which HS and IMI compromise fertility, which enable developing new strategies to mitigate these effects. For instance, treatment with GnRH and PGF2α to induce follicular turnover successfully improved conception rate in subpopulations of HS cows during the summer, in particular, primiparous cows and cows with high BCS. The "Ovsynch" program, also based on the use of GnRH and PGF2α, has been shown to improve conception rate of subclinical mastitic cows, most likely due to better synchronization of timing of ovulation with that of AI. Supplementing progesterone after AI improves conception rate of HS cows, particularly those with postpartum uterine disease and low BCS. It should be noted that similarities between the 2 stressors do not necessarily suggest a shared mechanism. Although not clear enough, an additive deleterious effects of HS and IMI on reproduction is suggested.

Invited review: Role of bacterial endotoxins in the etiopathogenesis of periparturient diseases of transition dairy cows

The dairy industry continues to suffer severe economic losses due to the increased disease incidence cows experience during the transition period. It has long been the classical view that the major contributing factor to the development of these periparturient diseases is the considerable increase in nutritional demands for milk production. This classical view, however, fails to account for the substantial correlation between both metabolic and infectious diseases and the detrimental effects that can occur with the provision of high-energy diets to support these nutritional demands. Currently, increasing evidence implicates bacterial endotoxins in the etiopathology of most periparturient diseases. Bacterial endotoxins are components of the outer cell wall of gram-negative and gram-positive bacteria that are highly immunostimulatory and can trigger proinflammatory immune responses. The ability of endotoxins to translocate from the mucosal tissues, including the gastrointestinal tract, mammary gland, and uterus, into the systemic circulation has been observed. Once they have entered the circulation, endotoxins potentially contribute to disease either directly, through eliciting an inflammatory response, or indirectly through other factors such as the overreaction of the natural protective mechanisms of the host. Although the evidence implicating a role of endotoxins in the pathogenesis of transition diseases continues to grow, our current knowledge of the host response to mucosal endotoxin exposure and pathogenic mechanisms remain largely unknown. Developing our understanding of the connection between endotoxemia and dairy cattle disease holds significant potential for the future development of preventative measures that could benefit the productivity of the dairy industry as well as animal welfare.

Carryover Effects of Acute DEHP Exposure on Ovarian Function and Oocyte Developmental Competence in Lactating Cows

We examined acute exposure of Holstein cows to di(2-ethylhexyl) phthalate (DEHP) and its carryover effects on ovarian function and oocyte developmental competence. Synchronized cows were tube-fed with water or 100 mg/kg DEHP per day for 3 days. Blood, urine and milk samples were collected before, during and after DEHP exposure to examine its clearance pattern. Ovarian follicular dynamics was monitored through an entire estrous cycle by ultrasonographic scanning. Follicular fluids were aspirated from the preovulatory follicles on days 0 and 29 of the experiment and analyzed for phthalate metabolites and estradiol concentration. The aspirated follicular fluid was used as maturation medium for in-vitro embryo production. Findings revealed that DEHP impairs the pattern of follicular development, with a prominent effect on dominant follicles. The diameter and growth rate of the first- and second-wave dominant follicles were lower (P < 0.05) in the DEHP-treated group. Estradiol concentration in the follicular fluid was lower in the DEHP-treated group than in controls, and associated with a higher number of follicular pathologies (follicle diameter >25 mm). The pattern of growth and regression of the corpus luteum differed between groups, with a lower volume in the DEHP-treated group (P < 0.05). The follicular fluid aspirated from the DEHP-treated group, but not the controls, contained 23 nM mono(2-ethylhexyl) phthalate. Culturing of cumulus oocyte complexes in the follicular fluid aspirated from DEHP-treated cows reduced the proportion of oocytes progressing to the MII stage, and the proportions of 2- to 4-cell-stage embryos (P < 0.04) and 7-day blastocysts (P < 0.06). The results describe the risk associated with acute exposure to DEHP and its deleterious carryover effects on ovarian function, nuclear maturation and oocyte developmental competence.

Subclinical mastitis disrupts oocyte cytoplasmic maturation in association with reduced developmental competence and impaired gene expression in preimplantation bovine embryos

Subclinical chronic mastitis was induced to examine the effects on oocyte developmental competence. Uninfected Holstein cows were intramammary administrated with serial (every 48h for 20 days) low doses of toxin of Staphylococcus aureus origin (Gram-positive; G+), endotoxin of Escherichia coli origin (Gram-negative; G-) or sterile saline (control). Follicular fluid of toxin- and saline-treated cows was aspirated from preovulatory follicles and used as maturation medium. Oocytes harvested from ovaries collected at the abattoir were matured and then fertilised and cultured for 8 days. The percentage of oocytes undergoing nuclear maturation, determined by meiotic nuclear stages, did not differ between groups. Cytoplasmic maturation, determined by cortical granule distribution, was affected by both toxins (PPPPTGS2) mRNA increased, whereas that of growth differentiation factor 9 (GDF9) decreased in matured oocytes. In addition, PTGS2 expression increased and POU class 5 homeobox 1 (POU5F1) expression decreased in 4-cell embryos developed from both G+ and G- oocytes. Thus, regardless of toxin type, subclinical mastitis disrupts oocyte cytoplasmic maturation and alters gene expression in association with reduced developmental competence.

Effects of mono(2-ethylhexyl)phthalate on cytoplasmic maturation of oocytes--The bovine model

Phthalates are known reproductive toxicants, but their intracellular disruptive effects on oocyte maturation competence are less known. We studied the potential risk associated with acute exposure of oocytes to mono(2-ethylhexyl)phthalate (MEHP). First, bovine oocytes were matured in vitro with or without 50 μM MEHP and examined for mitochondrial features associated with DNA fragmentation. MEHP increased reactive oxygen species levels and reduced the proportion of highly polarized mitochondria along with alterations in genes associated with mitochondrial oxidative phosphorylation (CYC1, MT-CO1 and ATP5B). In a second set of experiments, we associated the effects of MEHP on meiotic progression with those on cytoplasmic maturation. MEHP impaired reorganization of cytoplasmic organelles in matured oocytes reflected by reductions in category I mitochondria, type III cortical granules and class I endoplasmic reticulum. These alterations are associated with the previously reported reduced developmental competence of MEHP-treated bovine oocytes, and reveal the risk associated with acute exposure.