118 A retrospective analysis of follicular dynamics, LH, estradiol-17β, and progesterone in prostaglandin F_2α-induced estrus of Beetal goats

Abstract

The objective of the study was to reveal the factors associated with variable interval to ovulation following a single dose of prostaglandin F_2α (PGF2) in Beetal goats. In experiment 1, the extent of ovulation time was demonstrated after synchronizing Beetal goats (n = 38) by using a single injection of PGF2 based on corpus luteum detection by B-mode transrectal ultrasonography. Ovulations were detected every 6 h from PGF2 until ovulation. To explore the changes in follicular dynamics, endocrine profiles and behavioural events due to the variation in the interval to ovulation, another set of goats (n = 13; experiment 2) were synchronized by a single dose of PGF2 given at random days of the luteal phase. Follicular dynamics were monitored every 12 h from PGF2 until ovulation and oestrus was detected by apronized bucks every 6 h from PGF2 treatment. Blood sampling (3 mL) for oestradiol-17β and progesterone was done every 12 h from PGF2 until ovulation and every 2 h for LH assay by radioimmunoassay. Data were analysed by Student’s t-test, general linear models, and Pearson coefficient correlation (SPSS, version 20.0, SPSS Inc., Chicago, IL, USA). Results revealed that ovulation time varied from 60 to 96 h after PGF2, and 57% of ovulations occurred by 72 h after PGF2 (experiment 1). Based on this observation, goats (n = 13) in second experiment were retrospectively divided into early and late ovulators (i.e. 72 and 84 h following PGF2, respectively). Onset of oestrus, peak oestradiol-17β concentration, and LH surge after PGF2 were first observed in early than late ovulators (P < 0.05). The goats having greater follicle diameter and smaller corpus luteum diameter at the time of PGF2 ovulated earlier than late ovulators (5.4 ± 0.2 v. 4.3 ± 0.2 mm and 10 ± 0.6 v. 11.8 ± 0.3 mm, respectively; P < 0.05). Likewise, plasma progesterone concentration tended to be lower (P = 0.087) in early than late ovulators. However, interval from onset of oestrus to peak LH and ovulation, duration of standing oestrus, interval from LH peak to ovulation, diameter and growth rate of preovulatory follicles, and number of ovulations were similar (P > 0.05) between early and late ovulators. In conclusion, the size of dominant follicle and corpus luteum at the time of PGF2 determines the interval to ovulation following a single dose of PGF2 during the luteal phase.