Gonadotropin-Releasing Hormone (GnRH) and Its Agonists in Bovine Reproduction II: Diverse Applications during Insemination, Post-Insemination, Pregnancy, and Postpartum Periods.

The administration of GnRH and its agonists benefits various aspects of bovine reproductive programs, encompassing physiological stages such as estrous synchronization, post-insemination, pregnancy, and the postpartum period. The positive impact of GnRH administration in overcoming challenges like repeat breeder cows, early embryonic loss prevention, and the management of cystic ovarian disease (COD) is thoroughly surveyed. Furthermore, this review focuses on the significance of GnRH administration during the postpartum period, its role in ovulation induction, and how it enhances the productivity of embryo transfer (ET) programs. An emerging feature of this field is introduced, focusing on nano-drug delivery systems for GnRH agonists, and the potential benefits that may arise from such advancements are highlighted. While this review offers valuable insights into various applications of GnRH in bovine reproduction, it emphasizes the crucial need for further research and development in this field to advance reproductive efficiency and health management in dairy cattle.

Gonadotropin-Releasing Hormone (GnRH) and Its Agonists in Bovine Reproduction I: Structure, Biosynthesis, Physiological Effects, and Its Role in Estrous Synchronization.

GnRH is essential for the regulation of mammalian reproductive processes. It regulates the production and release of pituitary gonadotropins, thereby influencing steroidogenesis and gametogenesis. While primarily produced in the hypothalamus, GnRH is also produced in peripheral organs, such as the gonads and placenta. GnRH analogs, including agonists and antagonists, have been synthesized for the reproductive management of animals and humans. This review focuses on the functions of hypothalamic GnRH in the reproductive processes of cattle. In addition to inducing the surge release of LH, the pulsatile secretion of GnRH stimulates the pituitary gland to release FSH and LH, thereby regulating gonadal function. Various GnRH-based products have been synthesized to increase their potency and efficacy in regulating reproductive functions. This review article describes the chemical structures of GnRH and its agonists. This discussion extends to the gene expression of GnRH in the hypothalamus, highlighting its pivotal role in regulating the reproductive process. Furthermore, GnRH is involved in regulating ovarian follicular development and luteal phase support, and estrus synchronization is involved. A comprehensive understanding of the role of GnRH and its analogs in the modulation of reproductive processes is essential for optimizing animal reproduction.

Maximizing the reproductive performances of anestrus dairy buffalo cows using GnRH analogue-loaded chitosan nanoparticles during the low breeding season.

The present study was designed to evaluate the efficiency of GnRH-loaded chitosan-TPP nanoparticles (GnRH-CsNPs) to improve the reproductive performance of anestrus buffaloes during the summer. Egyptian buffaloes (n = 50) were synchronized for estrus either with the ovsynch protocol (OVSs, n = 20) or with the modified ovsynch protocol (OVSm, n = 30) using GnRH-CsNPs. Sera samples were collected on days 0, 7, and 10 (insemination day); and days15 and 30 post insemination for estradiol (E2) and progesterone (P4) determination. The follicles were monitored on day 0 and day 10. CLs diameter and pregnancy diagnosis were scanned on day 30 post insemination. Using a half dose of GnRH as GnRH-CsNPs in the OVSm improved (P < 0.05) the number of total and large follicles, and the total surface area of subordinate and large follicles compared to the OVSs protocol. The OVSm increased (P < 0.05) the largest follicles diameter on day 10 and CLs diameter on day 30 post insemination compared to the OVSs protocol. E2 concentration was greater (P < 0.05) on insemination day, and P4 concentrations were higher (P < 0.05) on days 15 and 30 post insemination in the OVSm than in the OVSs. The estrus induction rate was 80 % higher (P < 0.05) in the OVSm and cows exhibited estrus within 17.54 h earlier than the OVSs (50 % within 42 h), respectively. The conception rate increased in OVSm compared to OVSs (75 vs. 40 %, respectively). In conclusion, nanofabrication of GnRH allowed to reduce hormonal dose to 50 % without any adverse effects on fertility, and improved ovarian activity and reproductive performance of anestrus buffaloes during the low breeding season.

Improving Reproductive Performance and Health of Mammals Using Honeybee Products.

Honeybee products have positive effects on the reproductive performance of mammals. Many honeybee product constituents are biologically active, with antioxidant, antimicrobial, antiviral, anti-inflammatory, immunomodulatory, antifungal, wound-healing, and cardio-protective properties. Honeybee products also improve male and female fertility rates by enhancing gamete cryopreservation, in vitro maturation and fertilization, and embryo development. Previously published studies confirmed their efficacy for alleviating reproductive toxicity caused by contaminants and lifestyle habits that impair overall health and well-being. However, high-dose oral administration of honeybee products may adversely affect the reproductive system, and unfavorable effects were alleviated by treatment cessation. For this reason, this review proposes that bioactive components from bee products can be used as a strategy for improving the reproductive performance and health of mammals.

Efficiency of GnRH-Loaded Chitosan Nanoparticles for Inducing LH Secretion and Fertile Ovulations in Protocols for Artificial Insemination in Rabbit Does.

Gonadotropin-releasing hormone (GnRH)-loaded chitosan nanoparticles (GnRH-ChNPs) were used at different doses and routes of administration to induce ovulation in rabbits as an attempt to improve artificial insemination (AI) procedures and outcomes. In this study, the characteristics (size, polydispersity, loading efficiency, and zeta-potential) of GnRH-ChNPs and the GnRH release pattern were determined in an in vitro study. A first in vivo study assessed the pituitary and ovarian response to different GnRH-ChNPs doses and routes of administration (two i.m. doses, Group HM = 0.4 µg and Group QM = 0.2 µg, and two intravaginal doses, Group HV = 4 µg and Group QV = 2 µg) against a control group (C) receiving bare GnRH (0.8 µg). The HM, QM, and HV treatments induced an earlier LH-surge (90 min) than that observed in group C (120 min), whilst the QV treatment failed to induce such LH surge. The number of ovulation points was similar among treatments, except for the QV treatment (no ovulation points). A second in vivo study was consequently developed to determine the hormonal (progesterone, P4, and estradiol, E2) profile and pregnancy outcomes of both HM and HV treatments against group C. The treatment HM, but not the treatment HV, showed adequate P4 and E2 concentrations, conception and parturition rates, litter size, litter weight, and viability rate at birth. Overall, the use of GnRH-ChNPs allows for a reduction in the conventional intramuscular GnRH dose to half without compromising fertility. However, the addition of GnRH-ChNPs to semen extenders, although successfully inducing ovulation, has negative impacts on fertility. Thus, more studies are needed to explore this point and allow further adjustments.