Hormonal dynamics and follicular turnover in prepuberal Mediterranean Italian buffaloes (Bubalus bubalis)

The aim of this study was the investigation of hormonal and ovarian follicular dynamics in prepuberal buffaloes (Bubalus bubalis) bred in Italy. Eleven 5–9-month old buffalo calves ranging in weight from 122 to 270kg, maintained under controlled nutritional and environmental conditions, underwent 50 days of ultrasonographic ovarian follicular monitoring in the months of October–December. Blood sampling for E2 and FSH determination and ultrasonographic monitoring using a 7.5MHz linear probe and an ALOKA SSD-500 monitor were performed daily. No differences in any of the parameters under study were highlighted when calves were divided into two weight categories (<200 and >200kg) and thus data were pooled. In this study, values are reported as mean±S.D. A range of two–six regular follicular waves was reported among calves with an average of 4±1.1. Overall interval (days) between wave emergence was 9.9±2.8 and largest diameters (mm) of dominant and first subordinate follicles were 8.4±1.2 and 4.8±0.6, respectively (P<0.05). With the exception of one calf, some minor follicular waves (short waves or SWs; 1.6±1), lasting <10 days (6.1±1.2) were reported. They were monitored contemporaneously on the ovary contralateral (n=7) or ipsilateral (n=3) to the main follicular wave. Growth rate (mm per day) of dominant follicles (DF) was significantly faster than for corresponding subordinate follicles (SF) and follicles of SWs (1.08±0.2 versus 0.79±0.1 and 0.83±0.1, respectively, P<0.05). The static phase (days) lasted longer in DF compared to SF and SW (5.4±1.8 versus 2.4±1.2 and 2.6±1, respectively, P<0.05). The regressing phase (mm per day) was similar among DF, SF and SW (0.86±0.2, 0.94±0.2 and 0.84±0.1, respectively, P=0.09). Episodic spikes of E2 and FSH were reported, corresponding to wave development throughout the course of investigation. In conclusion, the majority of buffalo calves displayed a typical pattern of regular follicular development in conjunction with a dynamic trend of ovarian and hypophyseal hormones. Some minor follicle turnover was reported with parallel main follicular waves.