This study compares the factors associated with variable interval to oestrus and ovulation between early versus late ovulating goats following PGF
2α administration. The time of ovulation in Beetal goats (
n = 38) was monitored through transrectal ultrasound at every 6 hr following a single dose of PGF
2α (experiment 1). Variations in oestrus and ovulation times were further explored through the changes in follicular dynamics, endocrine profiles and behaviour in another set of goats (
n = 13) following single PGF
2α given randomly during the luteal phase (experiment 2). The ovulation time varied between 60 and 96 hr, and 57% of ovulations occurred by 72 hr following PGF
2α (experiment 1). Accordingly, the goats (
n = 13) in the second experiment were retrospectively divided either into early and/or late ovulating, that is, ≤72 and/or ≥84 hr following PGF
2α. The onset of oestrus, peak estradiol‐17β concentration and LH surge after PGF
2α was first observed in early than late ovulating goats (
p < 0.05). The goats ovulating early had larger follicle and smaller CL in diameter at the time of PGF
2α administration than those ovulating late (5.4 ± 0.2 vs. 4.3 ± 0.2 mm and 10 ± 0.6 vs. 11.8 ± 0.3 mm, respectively;
p < 0.05). Likewise, plasma progesterone concentration tended to be lower (
p = 0.087) in early than late ovulating goats. In conclusion, the size of dominant follicle and CL at the time of PGF
2a determines the interval to ovulation following a single dose of PGF
2a during the luteal phase.
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