Impact of pre-ovulatory follicle diameter on plasma estradiol, subsequent luteal profiles and conception rate in buffalo (Bubalus bubalis)

The present study was designed to investigate the impact of pre-ovulatory follicle (POF) diameter on the day of estrus on plasma estradiol concentration, subsequent luteal profile (corpus luteum, CL, diameter and plasma progesterone concentration) and conception rate in buffaloes. Twenty-eight buffaloes were synchronized with synthetic analogue of prostaglandin F2α (PGF2α) administered 11 days apart. Transrectal ultrasonography and jugular vein blood sampling was carried out on the day of estrus and on days 0 (day of ovulation), 5, 12, 16 and 21 post-ovulation. Out of 28 buffaloes, 11 (39.3%) were diagnosed pregnant on day 40 post-ovulation. Retrospective analysis revealed that the buffaloes getting pregnant had larger (p < 0.05) POF diameter. In fact, all the buffaloes (n = 5/5) having POF diameter between >14 and 16 mm conceived, whereas, conception rate in buffaloes with POF diameter between >12 and ≤14 mm (n = 6/17) or <12 mm (n = 0/6) was 35.3% and 0.0%, respectively. A positive correlation (r = 0.57, p < 0.05) was observed between POF diameter and plasma estradiol concentration at estrus. On day 5 post-ovulation, luteal profile was positively correlated (CL: r = 0.34, p < 0.05; plasma progesterone concentration: r = 0.27, p > 0.05) with POF diameter. Further, on the same day, plasma progesterone concentration was positively correlated (r = 0.47, p < 0.05) with CL diameter, however, this correlation was absent (r = 0.05, p > 0.05) during the subsequent luteal phase. Nevertheless, the post-ovulation luteal profile of pregnant buffaloes was higher (p < 0.05) compared to non-pregnant counterparts. In conclusion, the diameter of POF in buffaloes has positive impact on plasma estradiol concentration at estrus, post-ovulation luteal profile and conception rate. The diameter of CL can be used as an indicator of luteal function at early but not at mid or late luteal phase of estrus cycle in buffaloes.