Effect of superovulatory dose of FSH on follicular development, atresia, and endocrine changes during superovulation protocol in Sahiwal Zebu Cows

Abstract

Abstract Background In the recent past, the antral follicle count (AFC), of an ovary, has been indicated as an important phenotypic characteristic related to female fertility and closely correlated to the performance of in vivo and in vitro embryo production. However, most of the follicles undergo degeneration at the early antral stage rather than the preantral and preovulatory stages. FSH has been considered a follicle survival factor. Therefore, the present study aimed to find the effect of superovulatory dose of FSH on follicular development, atresia rate, endocrine changes, and super ovulatory estrus characteristics in Sahiwal cows. Methods A total of 24 Sahiwal cows were divided into two groups. Simulated and non-stimulated groups. In the stimulated group, Sahiwal donors (n = 12) were superstimulated using pFSH during the mid-luteal phase and the same number of cyclic Sahiwal cows (n = 12) were monitored through trans-rectal ultrasonography for comparative follicular-endocrine changes in the stimulated and non-stimulated group. Results At the initiation of FSH administration (10th day), on the day of prostaglandin (PG) injection (12th day), and at super ovulatory estrus (SOE/14th day) significantly greater number of small, medium, and large follicles were recorded, respectively. However, similar changes were not found on the respective days of the oestrus cycle in non-stimulated cows. The number of surface follicles undergoing atresia was significantly higher (P < 0.01) in the non-stimulated than in the stimulated group. On the day of SOE, the greater number of preovulatory follicles (POF) was positively correlated with the number of small follicles in the ovary at the initiation of superovulatory (SO) treatment and ovarian dimension at SOE. Conclusions The administration of pFSH increased the total number of the large follicle population by preventing the atresia of the small follicle and propelling the cohort of the follicle in a continuous growth phase thereby the significantly higher number of POF recorded on the day of SOE and contributing to increased peripheral E2 concentration. Thus, the majority of SO animals exhibited high estrus intensity for a prolonged period than normal cycling Sahiwal cows.