Diestrus
Diestrus is the longest period of the estrous cycle in the domestic animals, including, cow, sheep, goat, sow and mare. It is a mid luteal period, it is relatively long period of sexual quiescence (rest) between 2 successive estrous cycles in polyestrous animals.
In Diestrus period, the CL is fully developed, actively functional and the reproductive organs are under the dominant influence of progesterone for the preparation of the uterus for implantation of zygote and its growth as fetus.
LH is required for maintaining the CL in domestic animals. In rodents PRL is luteotropic.
The endometrium becomes thicker and glands hypertrophy. The cervix is constricted and the vaginal mucus is scanty and sticky. The mucus membrane of the vagina is pale. The uterine muscle is relaxed.
Late in this period, the corpus luteum begins to show regression. The endometrium and its glands atrophy or regress in size. In species that are not polyestrus, anestrum may occur.
In the non gravid uterus PGF2α is produced and it passes into the uterine vein, transferred to the ovarian artery and reach the CL by counter current exchange at the vein and artery. In CL the PGF interferes with the LH action and produces vasoconstriction and arrests blood supply producing luteolysis.
In the cow, mare, sow, ewe, doe, PGF2α is the natural luteolytic agent.
In the cat, dog and primates PGF2α is not luteolytic and CL is maintained for 35-70 days (pseudo pregnancy).
Following luteolysis, proestrus of the next estrus cycle is initiated. Corpus albicans represents the fibrosed CL of the previous cycle.
