Dissertation is devoted to the experimental substantiation of the safety of the use of serum and chorionic gonadotropins in comparison with the analogue of gonadotropin-releasing hormone for ovulatory stimulation of rabbits based on the determination of reproductive, morphological, and hormonal indicators during five consecutive reproductive cycles.
Dissertation was completed in 2018-2024 in the laboratories of the Department of Veterinary Surgery and Reproductology of the State Biotechnological University of the Ministry of Education and Science of Ukraine, the Department of Biotechnology of Reproduction of Agricultural Animals of the Institute of Animal Husbandry of the National Academy of Agrarian Sciences of Ukraine, “Analytika” medical laboratory (Kharkiv), Regional State Laboratory of the State Production and Consumer Service in Poltava region and the reproduction sector of the private rabbit farm of Bogodukhiv district of Kharkiv region.
With the use of serum gonadotropin, the average fertility rate in females of experimental group 1 was 65.9%, and in experimental group 2 – 59.7%, compared to control rabbits, in which this indicator was 61.7%. The combined administration of gonadotropins led to a decrease in reproductive capacity – in experimental group 3, the fertility rate was 48.6%, and in experimental group 4, it was only 40.2%.
Analysing the histomorphology of the ovaries of pregnant rabbits of the fifth reproductive cycle after the administration of a gonadotropin-releasing hormone analogue (control group), we note that luteal structures predominated. Follicular atresia was of two types: obliterative, characteristic of primary and secondary follicles, and cystic – in tertiary follicles. Yellow bodies of different generations were founding in the ovaries of pregnant rabbits, which was evidence of their functioning during several reproductive cycles.
Long-term use of serum gonadotropin at a dose of 40 IU led to a decrease in the functional reserve of the ovaries due to numerous apoptosis of oocytes not only in primary and secondary follicles, but also in primordial ones. At the same time, the thickness of the follicular zone of the cortical substance was noticeably reduced. At the places of atresed primordial and primary follicles, lacuniform cavities were found.
The main differences we noted in experimental group 2 were: a slightly larger number of primordial and primary follicles in the cortical substance, while a smaller part of oocytes had destructive changes, which indicates a decrease in the negative effect of the 25 IU dose on the functional reserve of the ovaries with its long-term use. A greater number of antral follicles with signs of hypersecretory activity of granulosa cells was determined. The number of corpora lutea of pregnancy was greater, and interstitial glandular tissue predominated among the luteal structures, as in experimental group 1, but its composition included endocrinocytes both at the stage of flourishing functional activity and at the stage of regression.
With the combined use of gonadotropins, the vascular reaction with signs of hyperemia and venous stasis was less pronounced. Most of the cortical and medullar vessels of the rabbits’ ovaries of experimental group 3 were dilated and looked empty. The pool of primordial follicles was more preserved compared to the ovaries of rabbits of experimental groups 1 and 2. It was significantly smaller compared to the control.
In the ovaries of rabbits after the combined use of gonadotropins in a dose of 24 IU against the background of the manifestation of the main biological effects determined in the rabbits of experimental group 3, microstructural features were established, indicating a high secretory activity of interstitial glandulocytes, compared to the ovaries of rabbits of all previous groups.
The hormonal background of rabbits underwent significant changes depending on the means of ovulation induction, its dosage and duration of administration. The safety of long-term use of the hormones for stimulation of ovulation in rabbits assessed by the content of sex hormones in the rabbit meat at the end of the experiment. The levels of testosterone and 17β-E were at the limit of the detectable level, while the content of 17β-E did not change, and testosterone had a slight tendency to increase. In general, the obtained results determined not only the scientific novelty of the dissertation research, but also the practical significance of the work, which is confirmed by the scientific and methodological recommendations “Use of hormonal agents in ovulation stimulation protocols in rabbits”
