Hares exhibit permanent pregnancy
While foxes have the reputation of being sluts in the furry fandom, perhaps this title should rather fall to hares, who have been shown to have simultaneous pregnancies.
The hares show superfetation — the ability to become pregnant before giving birth from an earlier pregnancy. Scientists at the Liebniz Institute for Zoo and Wildlife Research found that pregnant European brown hares can become pregnant again about four days before delivery. This decreases the amount of time between litters and makes the hares capable of being permanently pregnant.