Noun
(of animals having several estrous cycles in one breeding season) a state or interval of sexual inactivity or quiescence between periods of activity
Source: WordNetDepending on breed, on average, 16% of mares have double ovulations, allowing them to twin, though this does not affect the length of time of estrus or diestrus. Source: Internet
High progesterone levels (during diestrus) cause the cervix to close and become toned. Source: Internet
Becomes dry, and closes more tightly, during diestrus. Source: Internet