ollicles can be palpated throughout the Estrous cycle. This is because follicular growth occurs in waves throughout the Estrous Cycle.
When a cow ovulates, the depression left is termed a corpus hemorrhagicum and a group of follicles begin to grow. All follicular waves are proceeded by an increase in FSH (Follicular Stimulating Hormone). Over the next few days the corpus hemorrhagicum becomes a corpus luteum and secretes progesterone from day 5-18 of the Estrous Cycle and one follicle from the group of emerging follicles becomes dominant, and causes the regression of the remaining group of follicles. This dominant follicle secretes estradiol, but does not proceed to ovulation because of the presence of a corpus luteum secreting progesterone at this stage of the cycle (some cows might show estrus behavior at this stage because they are under the influence of some estradiol). When this first dominant follicle becomes non-functional, there is an increase of FSH and a second wave of follicles begins to grow and a new dominant follicle emerges.
The concentration of FSH is controlled by the secretion of estradiol and inhibin by the dominant follicle. As the concentration of estradiol secreted by the dominant follicle increases, the concentration of FSH decreases and LH (Leutininzing Hormone) is secreted in a pulsatile fashion.
When the dominant follicle is sufficiently developed it produces sufficient estradiol to cause an LH surge which causes ovulation. Only follicles greater than 10 mm will ovulate. The dominant follicle will only proceed to ovulation if its growth coincides with the regression of the corpus luteum caused by the release of Prostaglandin from the uterus and subsequent decreased levels of progesterone. Some cows have two waves of follicles before ovulation of a dominant follicle, and some cows have three waves of follicles before ovulation of a dominant follicle. Follicles that ovulate from three wave cycles might be more fertile than follicles that ovulate from two wave cycles because the follicles are younger. Some reproductive programs purposefully make cows have three waves of follicles.