Placentophagy, also known as placentophagia, is the act of consuming part or all of the afterbirth following parturition in mammals. Parturition involves the delivery of the neonate, as well as the placenta and fetal membranes. The placenta is a critical organ that develops in the maternal uterus during pregnancy to support the fetus. It connects to the fetus via the umbilical cord in order to allow nutrient transport, waste excretion and gas exchange between mother and fetus. The morphological features of the placenta differ among species, but the function is universal. The behaviour is characteristic to the mother of the majority of placental mammals. Significant documentation has been provided on placentophagy in a range of animals.

Anomalies generally include humans and aquatic species, as well as camels. However, the concept is becoming more popular among women in the West, despite its controversial overtone.

Theories as to why mammals engage in placentophagy are related to the many proposed benefits of placental consumption. These vary between animals but tend to be behavioural, medical or spiritual in nature.

Placentophagy is a normality in most members of the taxonomic group Eutheria. It has been observed in animals ranging from rodents to primates, and even in some instances humans. The most extensive study has been on animals in orders Rodentia, Chiroptera, Lagomorpha, Carnivora, Perissodactyla, Artiodactyla, and Primates. Exceptions to the ubiquitous behaviour in mammals can be seen in humans, sea mammals and camelids. It is suggested that the portion of marine species that do not practice placentophagy are ones that deliver their offspring in the water because beneficial components are dispersed upon expulsion from the mother, and that the domestication of camelids has eradicated the behaviour by placing stress and selective pressure on the species.

Placentophagia in rabbits is exclusively performed by maternal figures that have recently given birth. A study shows that even when pregnant and pre-parturient female rabbits are presented with placental meal there is little participation in the behavior but all postpartum mothers ate the afterbirth. When compared with the consumption of liver, another protein source, the occurrence of placentophagia alone increases by roughly 55% in the short 1–5 day period following parturition. The liver is preferential to non-pregnant, pregnant and pre-parturient mothers consistently as opposed to post-partum mothers who chose to consume only placenta when presented with both. The same study also looked at the interest of the placenta in pregnant rabbits, they saw that in the days leading up to delivery the animals were more intrigued by the placenta when it was presented, which was shown by increasing sniffing of the placenta. The attraction was not demonstrated towards the liver. This infers that there is a tie between elements prompting both delivery and placentophagy in pregnant maternal rabbits. In some instances placentophagia is tied to cannibalism in rabbits. As the mother engages in the act of consuming the placenta, they accidentally ingest the neonate as well.

Placentophagia has been studied most commonly in rodents, specifically rats. There have been multiple conclusions drawn from the available literature. One major finding is that the consumption of the afterbirth and associated materials increases the onset and intensity of maternal behavior in rats. The increased contact between the adult and the infant is what enhances the adoption of parental behavior. In addition to increasing the parenting tendencies of mother rats, it has been seen that placentophagia by female weanling laboratory rats when the mother births a subsequent litter, elevates alloparenting behavior toward their siblings. Additional research has shown that ingestion of the placenta and amniotic fluid influences the pain tolerance in pregnant rats via elevation of naturally occurring opioid-mediated analgesia. Production of endogenous opioids produced by the central nervous system, is increased during the birthing process which raises the pain threshold of the mother. When coupled with the ingestion of placenta or amniotic fluid, there is a drastic increase in the opioid effect. A test whereby rats were given meat rather than placenta supported the contribution of the afterbirth components to the enhanced opioid effect by showing no increase in the pain threshold of the post-partum mother.

There are numerous hypothesized benefits to the practice of placentophagy in both human and nonhuman mammals, which are seen as the direct motivation for various animals to engage in the consumption of the afterbirth. Many of these proposed benefits have since been disproved through scientific study.

Some initial conjectures related directly to the satiation of specific and general maternal hunger. These hinged on the idea that prior to parturition mothers ceased to eat and so, immediately after birth they consumed the placenta to satisfy an intense hunger. A further idea was that of specific hunger, according to which the maternal figure participated in placentophagy in order to replenish any resources depleted during pregnancy that were contained within the placenta. This was later disproved by studies on rats and other species showing that a wide range of animals do not typically decrease the amount of food or water taken in prior to delivery, and that rats presented with placenta will consume it regardless of pregnancy or virginity.