by Alice Swetnam
Ovarian cysts are large (>2.5cm), fluid filled structures that persist on the ovary for 10 days or more and cause abnormal reproductive behaviour due to secretion of either oestradiol (thin walled, follicular cysts) or progesterone (thick walled, luteal cysts). They arise when a mature follicle doesn’t ovulate or regress and the granulosa tissue degenerates. Cysts usually occur a few weeks postpartum with the first ovulation after calving. They are most common in older dairy cows, with low incidence in beef cows and heifers.