Ovarian follicular dynamics, progesterone concentrations, pregnancy rates and transcriptional patterns in Bos indicus females with a high or low antral follicle count

Abstract

We evaluated the effect of the antral follicle count (AFC) on ovarian follicular dynamics, pregnancy rates, progesterone concentrations, and transcriptional patterns of genes in Nelore cattle (Bos taurus indicus) after a timed artificial insemination (TAI) programme. Cows were separated based on the AFC, and those with a high AFC showed a larger (P < 0.0001) ovarian diameter and area than those with a very low AFC. Females with a very low AFC exhibited a larger (P < 0.01) diameter of the dominant follicle at TAI (13.6 ± 0.3 vs. 12.2 ± 0.4 mm) and a tendency (P = 0.06) to have different serum progesterone concentrations (2.9 ± 0.3 vs. 2.1 ± 0.3 ng/mL; on day 18, considering day 0 as the beginning of the synchronization protocol) than those with a high AFC. The pregnancy rate was higher (P ≤ 0.05) in animals with a very low (57.9%) and low (53.1%) AFC than in those with a high AFC (45.2%). The expression of genes related to intercellular communication, meiotic control, epigenetic modulation, cell division, follicular growth, cell maintenance, steroidogenesis and cellular stress response was assessed on day 5. In females with a low AFC, 8 and 21 genes in oocytes and cumulus cells, respectively, were upregulated (P < 0.05), while 3 and 6 genes in oocytes and cumulus cells, respectively, were downregulated. The results described here will help elucidate the differences in ovarian physiology and the reproductive success of Bos indicus females with a low or high AFC.

Low versus high antral follicle count on the fertility of timed AI Nelore heifers

“…Although the present study did not detect a difference in the P/AI between Low and High AFC heifers, another study performed with Nelore cows observed a negative association between AFC and P/AI (Morotti et al, 2018). In addition, Nelore females with high AFC had lower serum progesterone concentrations after ovulation and lower fertility in TAI programs (Lima et al, 2020). The difference in the cut-off to determine low and high AFC females could be another source of variation in the present study.…”

“…Several studies have estimated the relationship between AFC and fertility in B. indicus (Moraes et al, 2019;Morotti et al, 2018;Lima et al, 2020). However, the relationship between AFC, pubertal status, and fertility in heifers has not been deeply investigated.…”

Effect of ovarian follicular wave pattern and endocrine characteristics on pregnancy outcome in cows

“…In one such study, in vitro produced embryos from pre‐pubertal cow heifers exhibiting a high response (≥20 follicles) to exogenous gonadotropin stimulation, yielded 100% PRs (Taneja et al., 2000). Without taking into account the wave pattern, a higher follicular count favouring pregnancy has been linked to elevated luteal phase P4 concentration (de Lima et al., 2020; Jimenez‐Krassel et al., 2009), which in turn increased the endometrial thickness, interpreted as a better endometrial development favouring pregnancy (Jimenez‐Krassel et al., 2009). To the contrary, unchanged endometrial thickness in spite of higher P4 concentrations is also on record (Muth‐Spurlock et al., 2017).…”

“…pregnancy has been linked to elevated luteal phase P4 concentration(de Lima et al, 2020;Jimenez-Krassel et al, 2009), which in turn increased the endometrial thickness, interpreted as a better endometrial development favouring pregnancy(Jimenez-Krassel et al, 2009). To the contrary, unchanged endometrial thickness in spite of higher P4 concentrations is also on record(Muth-Spurlock et al, 2017).…”

Folliculogenesis, Fertility and Biotechnology in Dairy Cattle

“…In contrast, a high conception rate was observed after the use of TAI in low AFC females Bos taurus indicus compared to high AFC animals [43,44]. Additionally, other authors [45] observed that high AFC Bos taurus taurus females had lower fertility and shorter reproductive life than females with low AFC, but contrasting data have been reported [46].…”