Relationship between endogenous progesterone and follicular dynamics in lactating dairy cows with ovarian follicular cysts

Two experiments were conducted to examine circulating concentrations of progesterone (P,) in cows with ovarian follicular cysts (OFCs) and to relate differing levels of P, to subsequent follicular events. In experiment 1, peripheral concentrations of P, were determined in cows diagnosed with OFCs. Nonpregnant, lactating Holstein and Jersey cows (n = 32) were diagnosed as having OFCs by rectal palpation. Ovarian follicular cysts were then examined by transrectal ultrasonography to confirm the presence of OFCs (follicle diameter, greater than or equal to17 mm; absence of luteal tissue). At confirmation, a blood sample was collected for quantification of P-4. The concentration of P-4 at confirmation was classified as low (<0.1 ng/ml), intermediate (0.1-1.0 ng/ml), or high (1.0-2.0 ng/ml). More OFCs were associated with intermediate (66%) than with either low (28%) or high (6%) concentrations of P-4. In experiment 2. the fate of follicles (diameter, greater than or equal to10 mm) that formed in the presence of an OFC was determined and related to circulating concentrations of P-4 during follicular development. Follicles (n = 59) that formed in the presence of an OFC ovulated (n = 19), formed a cyst (n 30), or underwent normal growth and regression (NGR; n 10). Endogenous P-4 in the 7-day period during follicular development was classified as low (if P-4 dropped to <0.1 ng/ml for 1 day or longer), intermediate (if P-4 averaged between 0.1 and 1.0 ng/ml and never dropped to <0.1 ng/ml), or high (if P-4 averaged >1.0 ng/ml and never dropped to <0.1 ng/ml). In the presence of intermediate P-4, 75% of observed follicles formed cysts, compared with 10% that ovulated and 15% that experienced NGR. In the presence of low P-4, 53%, 41%, and 6% of follicles ovulated, formed a follicular cyst, or experienced NGR, respectively. Thus, an association between intermediate P-4 and the formation of OFCs was established.