Ovarian Function in Cows

Study Notes

The ovary is the primary female reproductive organ in female animals.
It's responsible for producing eggs (ova) and hormones like estrogen and progesterone.
Located in the abdominal cavity, each cow has two ovaries, oval-shaped, approximately 1-1.5 inches long.

Egg production is called oogenesis, a cyclic process that occurs within the estrous cycle (average 21 days).
The ovary contains thousands of primary follicles, each with a germ cell surrounded by cells.
Only a small percentage of these follicles develop into mature eggs.
Follicles undergo stages of development: primary, secondary, and tertiary.
During development, the follicle increases in size, forming a cavity and attaching the egg to the back of the follicle.
Mature follicles are called Graafian follicles (dominant follicles) and bulge from the ovary's surface.

Ovulation occurs when the Graafian follicle ruptures, releasing the egg and the corpus luteum.
The corpus luteum is crucial for producing progesterone.
After ovulation, follicle cells undergo luteinization, forming the corpus luteum.
The corpus luteum goes through its own maturation and regression cycle within the estrous cycle.
A corpus hemorrhagicum forms in the ruptured follicle and transforms into a corpus luteum by day 5 of the cycle.
The functional corpus luteum lasts from day 5 to day 15 of the cycle, secreting progesterone.
If pregnancy doesn't occur, the corpus luteum regresses, reducing progesterone levels, allowing for the next estrous cycle.
The regressed corpus luteum is known as the corpus albicans and remains visible on the ovary for several cycles.

After calving, cows typically experience a period of anestrus (no cycling), lasting around 60 days.
The duration of postpartum anestrus varies depending on factors like age, nutrition, lactation, calf presence, and stress.
A persistent corpus luteum is a condition where the corpus luteum doesn't regress normally despite non-pregnancy, and requires veterinary treatment.

Short estrous cycles (7 to 11 days) can occur due to the absence or dysfunction of the corpus luteum.
This results in low progesterone levels.

Hormones are secreted by endocrine glands and transported through blood and lymph.
Estradiol (estrogen) is produced by the granulosa cells of the follicle.
Estradiol influences: development of secondary sex organs, estrus behavior, growth, and regulation of puberty and postpartum anestrus.
Progesterone is secreted by the corpus luteum and suppresses ovulation.