In dairy cows, due to the degeneration of the epithelium of the unovulated follicles, the proliferation of the connective tissue of the follicle wall. The death of the oocytes, the increase of follicular fluid, and the increase of the follicle volume compared with the normal mature follicles form follicles, which are called follicular cysts.

It is mainly caused by excessive secretion of FSH and insufficient secretion of LH, which causes the follicles to overdevelop and fail to ovulate normally, forming large follicles. Some cysts also form multiple small cysts because the ovaries continue to produce new follicles. Most of them occur in dairy cows during the peak lactation period after delivery and 4-6 births.

During rectal examination, the diameter of the follicular cysts of cattle can reach 1.5 meters, the skin is thick and the internal fluid seems to be not full. During B-ultrasound examination of dairy cows, a large spherical liquid dark area can be seen on the ovaries.

In female animals with follicular cysts, due to the continuous secretion of FSH by the pituitary gland, the follicles are overdeveloped, and therefore a large amount of estrogen is secreted, which makes the female animals have strong estrus symptoms, highly restless spirits, mooing, refusing to eat, chasing, and climbing on other female animals, forming "male admiration". Because ovulation cannot occur, the estrus lasts for a long time. If it lasts too long, it is due to the degeneration of the follicle wall.

There are two sources of corpus luteum cysts: one is that the mature multi-day follicles fail to ovulate, and the follicle wall epithelium is luteinized, which is called luteinized cysts. The other is that after ovulation, due to some reasons, the corpus luteum is insufficiently luteinized, and a cavity is formed in the corpus luteum, and fluid accumulates in the cavity to form a corpus luteum cyst.

Because the corpus luteum cyst secretes progesterone, it inhibits the pituitary gland from secreting gonadotropin, so no follicles develop in the ovaries, so the female livestock does not show estrus. During rectal examination, the corpus luteum cyst is large (7-15cm), with thick and soft walls, and is not so tense. However, mature follicles, follicular cysts and corpus luteum cysts are often confused clinically. When using B-ultrasound examination of dairy cows, the formation of follicles is almost invisible on the ovaries, but liquid dark areas can be seen in the corpus luteum.