In mammalian species, pseudopregnancy is a physical state whereby all the signs and symptoms of pregnancy are exhibited,
The mechanism is not well understood, but prolactin and its receptors are known to be involved in pseudopregnancy.
Cats
Pseudopregnancy occurs when a female cat
Ovulation but is not
Fertilisation 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
Estrous cycle 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.
become pseudopregnant following an estrus in which the queen is bred by an infertile male. Queens are
, 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 increase until 2–3 days post copulation, then the level rises until day 21 post copulation where after it gradually declines to normal levels.
Dogs
Pseudopregnancy is a normal physiologic process that occurs in female
. It is seen 45–60 days after a normal
Estrous cycle (heat) period. After ovulation, progesterone levels rise. Pseudopregnancy 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 pseudopregnancy. Dogs may exhibit mothering of toys, nesting or aggression. Mammary development and milk production are common. Pseudopregnancy can also be acutely induced by
Neutering (removing of
Ovary) 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.
Swine
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. Pseudopregnancy can occur when all of the
embryo loss after the maternal recognition of pregnancy (days 10–15 postmating) and before fetal bone calcification (days 35–40 of gestation). The sow remains in
Estrous cycle 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 death machines, and
Doppler effect.
have been shown to be detrimental to sows and gilts by causing the female to retain a corpora lutea inhibiting cyclicity and causing a pseudopregnancy; as well as a constant exhibition of estrus, and infertility. Pregnant females produce litters that result in a higher number of stillborns, mummified fetuses, and abortions. Before breeding, ingesting mycotoxins mimics the action of estradiol-17β. Specifically, zearalenone binds to estrogenic receptors that would normally bind to estrogen, causing the female to exhibit constant estrus.
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
Nocturnality 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
Decidualization 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.
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.
Mice
Mice become pseudopregnant following an estrus in which the female is bred by an infertile male, resulting in sterile mating.
Like dogs, mice are spontaneous ovulators. 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. The female will develop
mammary glands,
lactation, and build nests in the pseudopregnant state. Pseudopregnancy in mice is somewhat common in
Laboratory mouse because it is often induced for the purpose of implanting embryos into a
Surrogacy, but is uncommon in wild mice because most wild males are fertile and will genuinely impregnate the female.
Further reading
