Formation and Treatment of Ovarian Follicular Cysts in Dairy Cows

Approximately 10-13% oflactating dairy cows develop ovarian follicular cysts, making it the most common reproductive disorder in dairy cows. Each occurrence of a cyst adds 22-64 additional days to the calving interval and costs dairymen approximately $137. Recently researchers have shown that low doses of progestagens can induce the formation of persistent follicles with physiological characteristics similar to ovarian follicular cysts. This has led us to propose that ovarian follicular cysts form due to inappropriate secretion of progesterone, either from the follicle destined to become a cyst or from existing cysts. In experiment la, we will monitor follicle growth by ultrasonography and measure progesterone concentrations during the early postpartum period in dairy cows, when the emergence of a cyst can be studied in the absence of other cysts. In experiment Ib, we will monitor follicle growth and measure progesterone concentrations during the normal breeding period (days 60-250 postpartum), When cysts frequently form in the presence of other cysts. In both experiments, \ve will retrospectively compare concentrations of progesterone during the four days prior to ovulation in cows that ovulate normally to concentrations during the comparable period in cows that form cysts. We suspect that the cows forming cysts may have higher concentrations of progesterone during this critical period of follicular development. In experiment 2, we will use intravaginal, progesterone releasing devices (CIDRs) to identify the lowest concentration of progesterone needed to get formation of persistent follicles. In experiment 3, we will administer a single injection of progesterone (200 mg) to Co\VSas a treatment for cysts. This treatment has been used previously to induce regression of persistent follicles formed by administering a low dosen progestogen.