During proestrus, which lasts for about 12 hours, the levels of estrogen in the bloodstream begin to rise, and the vaginal opening widens. Estrus is the stage when the female is most fertile, and it usually lasts for 24 hours. During this time, ovulation occurs, and the eggs are released from the ovaries.
Metestrus lasts for about 1 day, and during this time, the levels of progesterone in the bloodstream begin to rise. Diestrus is the longest stage of the estrous cycle and lasts for about 2 days.
During this time, the levels of progesterone remain high, and the uterus prepares for implantation of a fertilized egg.