Characterization of ovarian follicular cysts and associated endocrine profiles in dairy cows.

It is generally accepted that ovarian follicular cysts (cysts) are nonovulatory follicular structures that contribute to extended calving intervals. Follicle/cyst dynamics and the etiology of cysts are unclear. The present study was conducted to characterize follicle/cyst dynamics and to define endocrine changes (etiology) associated with cyst development. Thirty-two dairy cows were studied: controls (n = 6), cows with spontaneously occurring cysts (n = 14), and cows in which cysts were induced by exogenous steroid treatment (n = 12). Ovaries of cows were scanned daily by ultrasonography to record follicle/cyst dynamics. Blood was collected to determine endocrine changes associated with follicle/cyst life span. Three ovarian responses in cows with cysts were observed: persistence of cysts, turnover of cysts, or spontaneous recovery (self-recovered; turnover of cysts and replacement with a follicle that ovulated). Mean maximum size of cysts was larger (p < 0.05) than that of ovulatory follicles (2.80 + 0.19 vs. 1.60 0.05 cm). Mean interval from initial detection of follicle/ cyst wave to detection of a new follicle/cyst wave in cows with cysts was longer (13.0 1.1 days; p < 0.05) and more variable (6 to 26 days; p < 0.05) than in controls (8.5 0.5 days and 6-14 days, respectively). Cysts grew at the same rate as follicles but continued to grow for an additional period of time. A transient increase in FSH preceded detection of all follicle/cyst waves. Concentrations of LH (p < 0.01) and estradiol-170 (p < 0.05) were greater in cows with cysts than in cows in ovulatory cycles around the time of wave detection and around the time of ovulation or at the time when cysts reached a diameter equivalentto that of follicles that ovulated. In conclusion, cysts and follicles are dynamic structures, with cysts having longer intervals between wave detections compared to the interval in cows with normal estrous cycles. Greater concentrations of estradiol-17B and LH, but not FSH, were associated with development and persistence of cysts.