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.
Highlights
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
Despite numerous advances, many aspects related to female reproductive physiology remain unknown, especially those related to differences between subspecies (Bos taurus taurus vs Bos taurus indicus), as well as the particularities related to the antral ovarian follicle population and its influence on cattle fertility[12,13,14,15]
It was evidenced that the pregnancy rate in females with a low AFC is more than 10% that of those with a very high AFC when submitted to the TAI programme
Summary
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. Morotti et al.[8] revealed that certain aspects of ovarian follicular dynamics, such as a large dominant and ovulatory follicle diameter when undergoing TAI programmes, are more favourable for the low AFC group This positive correlation between dominant follicle size at the time of TAI and greater pregnancy rate is already well established[21,22,23], the specific reasons need to be better investigated at the cellular and molecular levels. The objectives of this study were as follows: (I) to evaluate the effect of a low/very low and high AFC on ovarian follicular dynamics and the pregnancy rate of cows submitted to the TAI programme and (II) to evaluate the transcriptional patterns of genes important to follicular cell development in heifers with low and high AFCs
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