Follicular and hormonal changes after estrous synchronization in bottlenose dolphins

Abstract

To gain more knowledge about the influence of hormone regulation on follicle development, ovarian ultrasounds were performed, and urinary hormone profiles were determined in ovulating and non-ovulating female bottlenose dolphins (n = 15) following estrus synchronization with altrenogest. Ovarian ultrasounds were conducted daily, post-synchronization to describe follicular recruitment in relation to the endocrine profile. Follicle sizes were grouped into very small (VSM), small (SM), medium (MD) and large (LG). In ovulating females, two follicular waves were identified, and follicular deviation toward establishing a dominant follicle only occurred during the second wave. For non-ovulating females, only the first wave was observed. For all urinary hormones, the non-ovulating group presented significantly lower concentrations of follicle-stimulating hormone (uFSH), luteinizing hormone (uLH), estrone conjugates (uE1-C) and estriol (uE3) but similar progestagen and cortisol concentrations compared to the ovulating group. Concentrations of uE1-C and uE3 and the numbers of MD and LG follicles significantly (P < 0.05) increased, while uFSH concentrations significantly (P < 0.05) decreased as ovulation approached. Urinary LH significantly increased concurrently with increasing numbers of LG follicles and decreasing numbers of SM follicles. The characterization of follicular development and its relationship with hormone assessment complements our understanding of follicular recruitment post-synchronization in bottlenose dolphins and provides new information concerning differences between ovulating and non-ovulating females in response to an estrous synchronization protocol.