Follicular dynamics and changes in oestradiol-17β, progesterone and LH profiles following PGF2α induced oestrus in early and late ovulating Beetal goats.

Abstract

This study compares the factors associated with variable interval to oestrus and ovulation between early versus late ovulating goats following PGF2α administration. The time of ovulation in Beetal goats (n=38) was monitored through transrectal ultrasound at every 6hr following a single dose of PGF2α (experiment 1). Variations in oestrus and ovulation times were further explored throughthe changes in follicular dynamics, endocrine profiles and behaviour in another set of goats (n=13) following single PGF2α given randomly during the lutealphase (experiment 2). The ovulation time varied between 60 and 96hr, and 57% of ovulations occurred by 72hr following PGF2α (experiment 1). Accordingly, the goats (n=13) in the second experiment were retrospectively dividedeither into early and/or late ovulating, that is, ≤72 and/or ≥84hr following PGF2α . The onset of oestrus, peak estradiol-17β concentration and LH surge after PGF2α was first observed in early than late ovulating goats (p<0.05). The goats ovulating early had larger follicleand smaller CL in diameter at the time of PGF2α administration than those ovulating late (5.4±0.2 vs. 4.3±0.2mm and 10±0.6 vs. 11.8±0.3mm, respectively; p<0.05). Likewise, plasma progesteroneconcentration tended to be lower (p=0.087) in earlythan late ovulating goats. In conclusion, the size of dominant follicle and CL at the time of PGF2a determines the interval toovulation following a single dose of PGF2a during the luteal phase.