Ovarian follicle dynamics and hormonal changes during early pregnancy in Saanen goats

Abstract

This study is aimed at describing the ovarian follicular dynamics, corpora lutea and their hormonal control during early pregnancy in Saanen goats. The ovaries of pregnant goats (n = 10) were monitored daily for follicles (≥ 2 mm) and corpora lutea by transrectal ultrasound over the 35 days after mating. Blood samples were collected by jugular venipuncture at the time of ultrasonography and were analysed for the concentrations of oestradiol (E₂) and progesterone (P₄), inhibin, FSH (follicle-stimulating hormone) and LH (luteinizing hormone). The pattern of follicular growth was characterised by five (n = 2; 20 %), six (n = 5; 50 %) and seven (n = 3; 30 %) follicular waves during early pregnancy. The first corpora lutea (size 6.8 ± 0.4 mm, mean + SEM) were detected at 5.0 ± 0.3 days after the mating with a maximum diameter (12.2 ± 0.3 mm) observed on day 24.0 ± 1.1 of pregnancy. The dominant follicle diameter of waves 1 and 4, and the duration of waves 1–4 and 7 were maximal during the early pregnancy period (P < 0.05). In addition, the inter-wave interval of the 5 waves was significantly (P < 0.05) longer compared to the six and seven inter-wave intervals (7.0 ± 0.1, 5.8 ± 0.1 and 5.0 ± 0.2 days, respectively). Although the number of small and medium-sized follicles did not differ with the days post-breeding, the number of large-sized follicles in the same period significantly decreased between 16 and 26 days and was negatively correlated with the period of pregnancy (P < 0.05). The plasma LH and E₂ concentrations were negatively correlated with the P₄ concentration. The inhibin concentrations were negatively correlated with FSH, but positively correlated with the number of large-sized follicles. These results indicate that ovarian follicular growth during the first 35 days of pregnancy in goats was characterised by a wave-like pattern and there was a close relationship between the number of FSH peaks and the number of follicular waves.