Effects of propylene glycol or elevated luteinizing hormone during follicle development on ovulation, fertilization, and early embryo development.

Seventeen nonlactating Holstein cows were superovulated in a Latin-square designed experiment to determine the effects of increased propylene glycol (PROP) and luteinizing hormone (LH) during antral follicle development on ovarian function, fertilization, and early embryo quality. PROP was orally drenched every 4 h for 7 days to induce hyperinsulinemia and associated metabolic changes. LH concentrations were altered by increasing LH (3-fold) during last 2 days of superovulation. Treatment groups were as follows: (1) control-oral drenching with water plus low-LH preparation; (2) high LH(HLH)-water plus HLH preparation; (3) PROP-drenching with PROP plus low LH; (4) PROP/HLH-PROP plus HLH. PROP increased glucose (P < 0.05) and insulin (P < 0.02) concentrations at all time points analyzed. Neither PROP nor LH affected numbers of follicles > 9 mm at time of gonadotropin-releasing hormone-induced LH surge, although percentage of these follicles that ovulated was decreased by both PROP (P = 0.002) and LH (P = 0.048). In addition, PROP tended (P = 0.056) to decrease total number of ovulations. PROP reduced (P = 0.028) fertilization rate, while LH tended (P = 0.092) to increase fertilization rate. There was no effect of either PROP or LH on any measure of embryo quality including percentage of embryos that were degenerate, quality 1, or quality 1 and 2 of total structures collected or fertilized structures. These results indicate that acute elevation in insulin during the preovulatory follicular wave can decrease percentage of large follicles that ovulate, particularly when combined with increased LH, and reduce fertilization of ovulated oocytes.

Use of a single injection of long-acting recombinant bovine FSH to superovulate Holstein heifers: a preliminary study.

Our objective was to compare several experimental preparations of a single injection of long-acting recombinant bovine FSH (rbFSH; types A and B) to a porcine pituitary-derived FSH (Folltropin) to superovulate Holstein dairy heifers. Nonlactating, nonpregnant virgin Holstein heifers (n = 56) aged 12 to 15 months were randomly assigned to one of four superstimulatory treatments. Beginning at a random stage of the estrous cycle, all follicles greater than 5 mm were aspirated. Thirty-six hours later, heifers received an intravaginal P4 device and superstimulatory treatments were initiated. Treatments were (1) 300 mg of pituitary-derived FSH (Folltropin) administered in eight decreasing doses over a period of 3.5 days; (2) a single injection of 50 µg of A-rbFSH; (3) a single injection of 100 µg of A-rbFSH; and (4) a single injection of 50 µg of B-rbFSH. All heifers received 25 mg PGF2α at 48 and 72 hours after the insertion of P4 device. At 84 hours after insertion, P4 devices were removed, and ovulation was induced 24 hours later with hCG (2500 IU). Heifers were inseminated at 12 and 24 hours after hCG treatment. The number of ovulatory follicles was greatest for heifers treated with Folltropin and B50-rbFSH, least for heifers treated with A50-rbFSH, and was intermediate for heifers treated with A100-rbFSH (25.7 ± 3.2, 18.9 ± 3.2, 5.9 ± 0.9, and 16.6 ± 3.1, respectively; P < 0.001). The number of corpora lutea was greatest for heifers treated with Folltropin, B50-rbFSH, and A100-rbFSH, and least for heifers treated with A50-rbFSH (19.1 ± 2.4, 16.1 ± 3.0, 15.9 ± 2.9, and 2.6 ± 0.9, respectively; P < 0.001). The number of good-quality embryos differed among treatments and was greatest for heifers treated with B50-rbFSH, Folltropin, and A100-rbFSH and least for heifers treated with A50-rbFSH (7.6 ± 2.4, 6.5 ± 1.7, 4.3 ± 1.5, and 0.8 ± 0.5, respectively; P < 0.001). In conclusion, a single injection of a preparation of long-acting rbFSH (either 100 µg of A-rbFSH or 50 µg of B-rbFSH but not 50 µg of A-rbFSH) produced similar superovulatory responses resulting in the production of good-quality embryos when compared with a pituitary-derived FSH preparation administered twice daily for 4 days. More studies using different types of cattle and different doses of rbFSH are needed to confirm the findings reported in this preliminary study.

Effect of maternal methionine supplementation on the transcriptome of bovine preimplantation embryos.

Maternal nutrition exclusively during the periconceptional period can induce remarkable effects on both oocyte maturation and early embryo development, which in turn can have lifelong consequences. The objective of this study was to evaluate the effect of maternal methionine supplementation on the transcriptome of bovine preimplantation embryos. Holstein cows were randomly assigned to one of two treatments differing in level of dietary methionine (1.89 Met vs. 2.43 Met % of metabolizable protein) from calving until embryo flushing. High quality preimplantation embryos from individual cows were pooled and then analyzed by RNA sequencing. Remarkably, a subtle difference in methionine supplementation in maternal diet was sufficient to cause significant changes in the transcriptome of the embryos. A total of 276 genes out of 10,662 showed differential expression between treatments (FDR <0.10). Interestingly, several of the most significant genes are related to embryonic development (e.g., VIM, IFI6, BCL2A1, and TBX15) and immune response (e.g., NKG7, TYROBP, SLAMF7, LCP1, and BLA-DQB). Likewise, gene set enrichment analysis revealed that several Gene Ontology terms, InterPro entries, and KEGG pathways were enriched (FDR <0.05) with differentially expressed genes involved in embryo development and immune system. The expression of most genes was decreased by maternal methionine supplementation, consistent with reduced transcription of genes with increased methylation of specific genes by increased methionine. Overall, our findings provide evidence that supplementing methionine to dams prior to conception and during the preimplantation period can modulate gene expression in bovine blastocysts. The ramifications of the observed gene expression changes for subsequent development of the pregnancy and physiology of the offspring warrant further investigation in future studies.

Effect of glucocorticoid-induced insulin resistance on follicle development and ovulation.

Polycystic ovarian syndrome (PCOS) is characterized by hyperandrogenemia, polycystic ovaries, and menstrual disturbance and a clear association with insulin resistance. This research evaluated whether induction of insulin resistance, using dexamethasone (DEX), in a monovular animal model, the cow, could produce an ovarian phenotype similar to PCOS. In all of these experiments, DEX induced insulin resistance in cows as shown by increased glucose, insulin, and HOMA-IR (homeostasis model assessment of insulin resistance). Experiment 1: DEX induced anovulation (zero of five DEX vs. four of four control cows ovulated) and decreased circulating estradiol (E2). Experiment 2: Gonadotropin-releasing hormone (GnRH) was administered to determine pituitary and follicular responses during insulin resistance. GnRH induced a luteinizing hormone (LH) surge and ovulation in both DEX (seven of seven) and control (seven of seven) cows. Experiment 3: E2 was administered to determine hypothalamic responsiveness after induction of an E2 surge in DEX (eight of eight) and control (eight of eight) cows. An LH surge was induced in control (eight of eight) but not DEX (zero of eight) cows. All control (eight of eight) but only two of eight DEX cows ovulated within 60 h of E2 administration. Experiment 4: Short-term DEX was initiated 24 h after induced luteal regression to determine if DEX could acutely block ovulation before peak insulin resistance was induced, similar to progesterone (P4). All control (five of five), no P4-treated (zero of six), and 50% of DEX-treated (three of six) cows ovulated by 96 h after luteal regression. All anovular cows had reduced circulating E2. These data are consistent with DEX creating a lesion in hypothalamic positive feedback to E2 without altering pituitary responsiveness to GnRH or ovulatory responsiveness of follicles to LH. It remains to be determined if the considerable insulin resistance and the reduced follicular E2 production induced by DEX had any physiological importance in the induction of anovulation.