Metestrus

Metestrus is the transitional period between ovulation and full development of the corpus luteum. During this period, the reproductive system switches from estrogen to progesterone dominance.

It is the post ovulatory phase during which the granulosa and thecal cells lining the ruptured follicles begin to grow and reorganize into a structure called the corpus luteum (CL), corpus lutem hemorrhagicum, which is the principal site of progesterone production.

CL grows rapidly from the granulose cells of the ruptured follicles under the influence of LH of the anterior pituitary

Metestrum or Metestrus is largely under the influence of progesterone produced by the corpus luteum. This hormone, by inhibiting the secretion of FSH by the pituitary gland, prevents the development of more Graafian follicles.

In the cow, during the early part of the metestrum, the epithelium over the caruncles of the uterus is very hyperemic and some capillary hemorrhage occurs. This is called post estrual or metestral bleeding. This is due to the estrogen withdrawal.

The mucus secretion decreases and the glands of the endometrium grow rapidly. Towards the end of metestrum. The uterus becomes soft and pliable, due to the relaxation of the uterine muscles.

In the species, cow, sheep and sow and mare, the length of metestrum is about equal to the time it take for the ova to reach the uterus or about 3-4 days.

In dogs and cat the pseudo pregnant period may last about 50-60 days and 30 to 40 days respectively, when, the CL regresses and an anestrum of varying length occurs.

In the queen that is not bred, ovulation, and CL development doesn’t occur and the follicle become atretic. several cycles of this sort may occur in the cat before a period of anestrum sets in. Dogs and Cats do not have diestrual periods.