In mammalian species, pseudopregnancy is a physical state whereby all the signs and symptoms of pregnancy are exhibited, with the exception of the presence of a fetus, creating a false pregnancy. The corpus luteum (the remains of an ovulated ovarian follicle) is responsible for the development of maternal behavior and lactation, which are mediated by the continued production of progesterone by the corpus luteum through some or all of pregnancy. In most species, the corpus luteum is degraded in the absence of a pregnancy. However, in some species, the corpus luteum may persist in the absence of pregnancy and cause "pseudopregnancy", in which the female will exhibit clinical signs of pregnancy. The mechanism is not well understood, but prolactin and it’s receptors are known to be involved in pseudopregnancy. The role of prolactin in maintaining pseudopregnancy is evident. For instance in the rodent, if chronic prolactin is administered the pseudopregnancy will continue, whereas the condition only lasts a few days if not administered. Cats Pseudopregnancy occurs when a female cat ovulates but is not fertilised due to breeding with an infertile male, spontaneous ovulation or due to the owner stimulating ovulation. The corpus luteum is present after ovulation and persists for around 37 days. The length of pseudopregnancy varies greatly with the mean duration being 41 days. After pseudopregnancy, the female cat returns to proestrus and can become pregnant again. The pseudopregnancy lasts around half the length of a normal pregnancy in cats. This is advantageous to cats as they can conceive earlier making them more efficient in reproduction. Cats become pseudopregnant following an estrus in which the queen is bred by an infertile male. Queens are induced ovulators, meaning that they will only ovulate and produce a corpus luteum if they are bred. The corpus luteum persists as if the queen were pregnant because the queen's body cannot distinguish between the pregnant and non-pregnant state (aside from the initial mechanical trigger of coitus). Pseudopregnant queens rarely show any mammary enlargement or behavioral signs and therefore rarely require treatment. Pseudopregnancy in cats is uncommon as the queen must be bred by an infertile male to become pseudopregnant, compounded by the fact that cats are seasonal breeders. The progesterone and estradiol profiles in pseudopregnancy are very different when compared to normal pregnancy. During pseudopregnancy, estradiol increases straight after mating and then decreases to normal levels. The amount of progesterone does not