Pseudopregnancy

Most species require signals from an embryo (such as IFN-τ in ruminants) to alert the female's body of a pregnancy.

This maternal recognition of pregnancy will cause persistence of the corpus luteum and the development of characteristics and behaviors necessary to care for offspring.

Pseudopregnant dogs will develop their mammary glands, lactate, and build nests to varying degrees depending on breed.

[9] Pseudopregnancy or "not-in-pig" is a condition that occurs when females exhibit physiological and behavioral signs associated with pregnancy, but there are no fetuses present.

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.

Pregnant females produce litters that result in a higher number of stillborns, mummified fetuses, and abortions.

The corpus luteum is known as a site of progesterone production in order for the uterus undergoes a decidual process.

The multiple intromission coital pattern initiates the neuroendocrine reflex which results in the sufficient progesterone secretion in pseudopregnancy.

[14] 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.

[14] Mice become pseudopregnant following an estrus in which the female is bred by an infertile male, resulting in sterile mating.

However, they will not become pseudopregnant following an estrus in which the female does not mate because the corpus luteum will degrade rapidly in the absence of coitus.

When the female is mated by an infertile male, the corpus luteum persists without an embryo, leading to pseudopregnancy.