Morphological assessment of ovaries during stimulation of ovulation in rab-bits with equine serum gonadotropin in different doses

Abstract

Ovulatory stimulation of rabbits during artificial insemination requires the use of hormonal drugs to stimulate maturation of follicles, effective fertilization and full manifestation of female sexual function. For this purpose, gonadotropins or analogues of gonadotropin-releasing hormone are common in the practice of rabbit breeding. The latter have a selective effect on folliculogenesis and, under certain conditions, are not capable of inducing ovulation in rabbits of “zero” reproductive cycle, that is, those that have not given birth. Instead, gonadotropins, in particular serum gonadotropin obtained from foal mares (eCG), have a pronounced effect on folliculogenesis in animals. eCG is a glycoprotein hormone secreted by trophoblastic epithelial cells of fetal origin. In other species, except for horses, it is able to induce the release of both luteinizing and follicle-stimulating hormone. That is why eCG is widely used together with human chorionic gonadotropin to induce follicle growth and ovulation. However, there are data on complications and pathological conditions that may occur with long-term use of eCG, especially in genital tract. Therefore, the goal of our research was the morphological evaluation of the functional compartments of ovaries when using eCG to stimulate reproductive function of rabbits. Schemes of hormonal treatment of females in the conditions of a private rabbit farm, an experiment was conducted, which included the introduction of eCG in different doses (40 IU for animals of experimental group 1 and 25 IU for experimental group 2) during five reproductive cycles. Selection of material for histological studies, its fixation, production and analysis of tissue sections stained with hematoxylin and eosin were performed according to commonly used methods. The complex of morphofunctional changes in the ovaries of the rabbits of experimental groups corresponds to the pathomorphological picture of the syndrome of hyperstimulated ovaries. In our experiment, obtained changes were more pronounced at a dose of 40 IU, using which we additionally detected signs of increased immunoreactivity in body of rabbits, as evidenced by the presence of nodular lymphoid formations in outer theca of secondary and tertiary follicles. Thus, as a safe regimen for the use of eCG for ovulatory stimulation in rabbits, we recommend a dosage of 25 IU for 1–2 reproductive cycles.