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= Pseudopregnancy =

Pseudopregnancy is the term used to describe a false pregnancy in the wider mammalian species. It is a physical state whereby all the signs and symptoms of pregnancy are exhibited, with the exception of the presence of a foetus. In humans this state is called pseudocyesis, with this term being derived from the Greek pseudes (false) and kyesis (pregnancy). Symptoms of pseudopregnancy can range from abdominal enlargement to experiencing the sensation of foetal movement. Whilst a simulated pregnancy occurs when a woman, knowing she is not pregnant, claims to be so and the presence of a tumour can alter the endocrine environment, resulting in physical changes similar to those observed in pregnancy, pseudopregnancy is distinct from these other forms of false pregnancy.

Pseudopregnancy in Cats
Domestic cats are a species that can become pseudopregnant. This 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. In pseudo pregnancy in cats the corpus luteum is present after ovulation and persists for around 37 days. The length of pseudopregnancy varies in cats greatly with the mean duration being 41 days. After pseudopregnancy, the female cat returns to proestrus and can become pregnant again. The pseudo-pregnancy lasts around half the length of a normal pregnancy in cats which does not occur in all other species such as dogs. This is advantageous to the cats as they can conceive earlier making them more efficient in reproduction. In cats, the progesterone and estradiol profiles in pseudo-pregnancy are very different when compared to normal pregnancy. During Pseudopregnancy estradiol increased straight after mating and then decreased returning to normal levels. The amount of progesterone did not increase until 2-3 days post copulation, then the level rises until day 21 post copulation where after it gradually declined returning to normal levels.

Pseudopregnancy in Dogs
Pseudo-pregnancy is a normal physiologic process that occurs in female dogs. It is seen 45-60 days after a normal estrous (heat) period. After ovulation, progesterone levels rise. Pseudo-pregnancy happens when the progesterone levels begin to fall as decreasing progesterone leads to an increase of the hormone prolactin. Prolactin is responsible for the behaviours seen during pseudo-pregnancy. Dogs may exhibit mothering of toys, nesting or aggression. Mammary development and milk production are common. Pseudopregnancy can also be acutely induced by spaying (removing of ovaries) a dog near the end of estrus. Spaying removes the source of progesterone and induces a rise in prolactin.

Permanent prevention of pseudopregnancy is accomplished with spaying.

Pseudopregnancy in Swine
Pseudopregnancy or "Not-in-Pig" is a condition that occurs when female exhibit physiological and behavioral signs associated with pregnancy, but there are no fetuses present. Pseudopregnancy can occur when all of the embryos are resorbed after the maternal recognition of pregnancy (days 10-15 postmating) and before fetal calcification (days 35-40 of gestation). The sow remains anestrus for prolonged periods, often as long as 115 days. These animals may exhibit varying degrees of udder development, but fail to deliver any pigs. The timely identification and removal of non-pregnant females from the breeding herd is important because it reduces both non-productive sow days and production costs.

Techniques used for pregnancy diagnosis in swine include ultrasonography, amplitude depth machines, and Doppler machines.

Neuroendocrine Pathway of Pseudopregnancy in Rats
The initiation of pseudopregnancy is basically similar to the pregnancy regarding the activation of progestational state. The neuroendocrine pathway of pseudopregnancy in rats is mainly initiated by the nocturnal surge of prolactin. The hormone prolactin produced regulates the activation and early maintenance of corpus luteum. The corpus luteum is known as a site of progesterone production in order for the uterus undergoes a decidual process. There are two types of induced pseudopregnancy; coitally induced pseudopregnancy and non-coitally induced pseudopregnancy. The coitally induced pseudopregnancy is stimulated by the action of copulation. The copulation stimulation causes the nocturnal prolactin elevation which then activates the corpus luteum. The multiple intromission coital pattern initiates the neuroendocrine reflex which results in the sufficient progesterone secretion in pseudopregnancy. However, induction of pseudopregnancy requires adrenergic system to be activated and simultaneously inhibits the cholinergic system.

The non-coitally induced pseudopregnancy requires the presence of the initial stimulus until the levels of progesterone are sufficiently elevated to produce positive feedback on secretion of prolactin. The initial stimulus can be in a form of some socio-environmental factors, such as concaveation with foster pups in virgin rats or cohabitation in all-female groups in mice.