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 A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

, creating a false pregnancy. The

corpus luteum The corpus luteum (Latin for "yellow body"; : corpora lutea) is a temporary endocrine structure in female ovaries involved in the production of relatively high levels of progesterone, and moderate levels of estradiol, and inhibin A. It is the ...

(the remains of an ovulated

ovarian follicle An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. In humans, women have approximately 200,000 to 300,000 follicles at the time of puberty, ea ...

) is responsible for the development of maternal behavior and

lactation Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process naturally occurs with all sexually mature female mammals, although it may predate mammals. The process ...

, which are mediated by the continued production of

progesterone Progesterone (; P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...

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 Prolactin (PRL), also known as lactotropin and mammotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secr ...

and its 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 Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a zygote and initiate its development into a new individual organism or off ...

due to breeding with an infertile male, spontaneous ovulation or due to the owner stimulating ovulation. The

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. Cat November 2010-1a

Cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

s become pseudopregnant following an estrus in which the

queen Queen most commonly refers to: * Queen regnant, a female monarch of a kingdom * Queen consort, the wife of a reigning king * Queen (band), a British rock band Queen or QUEEN may also refer to: Monarchy * Queen dowager, the widow of a king * Q ...

is bred by an infertile male. Queens are

induced ovulator Induced ovulation occurs in some animal species that do not ovulate cyclically or spontaneously. Ovulation can be induced by externally-derived stimuli during or before mating, such as sperm, pheromones, or mechanical stimulation during copulati ...

s, 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

and

estradiol Estradiol (E2), also called oestrogen, oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of female reproductive cycles such as estrous and menstrual cycles. Estradiol is responsible ...

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

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...

s. It is seen 45–60 days after a normal

estrous The estrous cycle (, originally ) is a set of recurring physiological changes induced by reproductive hormones in females of mammalian subclass Theria. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases ...

(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 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

spaying Neutering, from the Latin ('of neither sex'), is the removal of a non-human animal's reproductive organ, either all of it or a considerably large part. The male-specific term is castration, while spaying is usually reserved for female animals. Co ...

(removing of

ovaries The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...

) 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.

Dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...

s become pseudopregnant following an

estrus The estrous cycle (, originally ) is a set of recurring physiological changes induced by reproductive hormones in females of mammalian subclass Theria. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phas ...

phase in which the female dog is not bred, or in which she is bred by an infertile male. Most species require signals from an embryo (such as IFN-τ in

ruminant Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microb ...

s) 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. Recent research suggests that progesterone secretion is similar in pregnant and non-pregnant female dogs, so veterinary researchers hypothesize that they may not require molecular factors from the embryo for maternal recognition of pregnancy, and instead the corpus luteum persists regardless of pregnancy. Since the corpus luteum is not degraded, it will cause the development of maternal characteristics in the absence of pregnancy. Pseudopregnant dogs will develop their

mammary glands A mammary gland is an exocrine gland that produces milk in humans and other mammals. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in primates (for example, human ...

, lactate, and build

nest A nest is a structure built for certain animals to hold Egg (biology), eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of ...

s to varying degrees depending on breed. Although female dogs usually only cycle once or twice per year, pseudopregnancy is common.

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 embryos are resorbed after the maternal recognition of pregnancy (days 10–15 postmating) and before fetal bone calcification (days 35–40 of gestation). The sow remains in anoestrus for prolonged periods, often as long as 115 days. These animals may exhibit varying degrees of

udder An udder is an organ formed of two or four mammary glands on the females of dairy animals and ruminants such as cattle, goats, and sheep. An udder is equivalent to the breast in primates, elephantine pachyderms and other mammals. The udder is ...

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 Medical ultrasound includes diagnostic techniques (mainly imaging) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints, ...

, amplitude depth machines, and Doppler machines.

Mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξικός , "poisonous") is a toxic secondary metabolite produced by fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' is usually rese ...

s 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 Zearalenone (ZEN), also known as RAL and F-2 mycotoxin, is a potent estrogenic metabolite produced by some ''Fusarium'' and '' Gibberella'' species. Specifically, the '' Gibberella zeae'', the fungal species where zearalenone was initially detec ...

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

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

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. London_Scruffy_Rat

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 Cohabitation is an arrangement where people who are not legally married live together as a couple. They are often involved in a Romance (love), romantic or Sexual intercourse, sexually intimate relationship on a long-term or permanent basis. ...

in all-female groups in mice.

Mice

Mice A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

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 Sexual intercourse (also coitus or copulation) is a sexual activity typically involving the insertion of the Erection, erect male Human penis, penis inside the female vagina and followed by Pelvic thrust, thrusting motions for sexual pleasure ...

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

, lactate, and build nests in the pseudopregnant state. Pseudopregnancy in mice is somewhat common in

laboratory mice The laboratory mouse or lab mouse is a small mammal of the order Rodentia which is bred and used for scientific research or feeders for certain pets. Laboratory animal sources for these mice are usually of the species ''Mus musculus''. They a ...

because it is often induced for the purpose of implanting embryos into a surrogate dam, but is uncommon in wild mice because most wild males are fertile and will genuinely impregnate the female.

References