Ovarian follicular dynamics and hormonal profiles in heifer and mixed-parity Mediterranean Italian buffaloes (Bubalus bubalis) following an estrus synchronization protocol

The primary objective was to elucidate ovarian follicular dynamics and hormonal profiles in nulliparous heifer (HE; n=11) and mixed-parity (MP; n=10) Mediterranean Italian water buffaloes (Bubalus bubalis) following an estrus synchronization protocol. Both groups received a progesterone releasing intravaginal device (PRID) implant for 10 days; a luteolytic dose of synthetic prostaglandin was given 7 days after PRID insertion. Daily ultrasound monitoring and collection of blood to determine plasma concentrations estradiol and progesterone started 1 day after PRID removal and lasted for 55 and 65 days in HE and MP buffaloes, respectively. Data analysis was restricted to the first 5 days after PRID removal and to one estrus cycle following induced ovulation. The HE buffaloes were not inseminated and only one ovulated within 5 days after PRID removal; the remainder ovulated between 8 and 48 days after PRID removal (except one in which ovulation was never detected). All HP buffaloes were inseminated 72, 96 and 120h after PRID removal; seven buffaloes ovulated within 5 days after PRID removal and two were pregnant. Mean diameter of the largest follicle was significantly smaller in HE than MP buffaloes the first 4 days after PRID removal. There was a parity by time interaction (P=0.0047) for plasma progesterone concentrations; progesterone was higher in HE than MP buffaloes 1 day after PRID removal, but the converse was true 2 days after PRID removal. After induced ovulation, HE buffaloes exhibited a one-wave (n=5; length of cycle, 8–12 days), two-wave (n=4; range: 20–26 days) or three-wave cycle (n=1; 25 days). In contrast, all non-pregnant MP buffaloes (n=8) had a two-wave cycle (range: 19–25 days). For buffaloes with two-wave cycles, the growth rate and diameter of the largest follicle was significantly smaller in HE than MP buffaloes for both the first follicular wave (1.3mm versus 1.7mm per day and 10.5mm versus 13.3mm, respectively) and the second follicular wave (1.0mm versus 1.3mm per day and 11.0mm versus 13.8mm). In conclusion, there were many significant morphological and endocrine differences between HE and MP buffaloes.