Among domestic animals, cystic ovary disease is most common in cattle, particularly the dairy breeds, but it occurs sporadically in dogs (p 1279), cats, pigs, and perhaps mares. When diagnosing the reproductive status of mares, it must be remembered that normal follicle size during estrus is 4–6 cm in diameter. Ovulation failure can also be found in mares that are having irregular estrous cycles during the spring or fall transition phases of the reproductive cycle, but this situation is not treated in the same way as the cystic ovary disease condition of cattle. The granulosa cell tumor condition in mares causes marked enlargement of one ovary but differs from cystic ovary disease of cattle (see Reproductive Diseases of the Female Small Animal: Follicular Cysts in Small Animals).
Three ovarian structures in cattle include the term cyst: follicular cysts, luteal cysts, and cystic corpus luteum (CL). In contrast to the other 2, the structure described as a cystic CL (a CL with a cavity) arises after normal ovulation. Cystic CL are known to be a normal stage or variation of CL development because they are found in normally cycling and pregnant cows without concurrent abnormal reproductive performance. Cystic CL have a soft, mushy core area, due to presence of fluid from a degenerating blood clot, compared with the homogeneous, liver-like consistency of the base of a typical CL.
Cystic CL are most often detected 5–7 days after estrus when the structure is nearing the end of the corpus hemorrhagicum or growth phase. The cystic CL as well as the typical CL may or may not have an ovulation crown or papilla at its apex. Absence of this ovulation crown or papilla should not be considered diagnostic of the cystic condition because 10–20% of functional, normal CL fail to develop this feature. The two pathologic forms of bovine cystic ovary disease, follicular cysts and luteal cysts, are etiologically and pathogenetically related but differ clinically.
Last full review/revision July 2011 by Carlos A. Risco, DVM, DACT