Milk pretty much picks up where the placenta left off in terms of how a mammalian infant is provisioned by its mom. The most energetically demanding time for infants, the period just after birth, coincides with the transition of physiological transfer of nutrients being very efficient via the placenta to being much less efficient via lactation.
Where biochemical messages were once transferred between mom and baby through intimate placental connections, such messages were once transferred between mom and baby through intimate placental connections, such messages must now be transferred through the less-immediate lactation.
Colostrum and the Type of Placenta
The type of placenta in which the infant develops has an impact on several factors present in early milk, or colostrum.
Colostrum tends to be more protein-rich and lipid-poor than later milk, and it is also higher in immunoglobulins and other innate antimicrobial factors.
The level of dependency that a newborn has on colostrum consumption is highly associated with the specific type of placenta in which the neonate developed.
In cows, goats, horses, and deer that have epitheliochorial placentae (non-invasive ones that keep mom’s tissues separate from baby’s), the transfer of immunoglobulins from mom to offspring during pregnancy is impossible. This makes the ingestion of colostrum and associated immunoglobulins and other immune factors absolutely essential for newborn survival.
Carnivores that developed with an endotheliochorial placenta may also have had restricted gestational access to immune factors.
On the other hand, baby mammals like primates and humans that have developed with hemochorial placentae, in which there is major contact between the tissues of mother and offspring, have already received such immune factors during their gestation. This makes the ingestion of immune factors in colostrum less important.
How Long Does Colostrum Provisioning Last?
The duration of colostrum ingestion is an aspect of lactation that varies tremendously between mammalian species.
Ursids such as giant pandas give birth to the most underdeveloped offspring among the placental mammals. For these animals, and for many bear species, there is a lengthy colostrum phase to adequately provision the helpless newborn. Colostrum provision in the giant panda lasts for thirty days, which is long – especially in comparison to the 24-hour colostrum provisioning in gray seals or the one to two days that humans get.
The gut microbiome of newborn pandas undergoes almost a complete changeover in their first three to four weeks of life, which is a massive change that represents an extensive period of maternal investment.
Pandas have an adult diet that is exclusively comprised of bamboo, so newborns require extensive seeding of the “correct” bacteria in their guts to be able to effectively digest the vegetation.
Koalas Ingest Pap Instead
Something similar happens in a marsupial – the koala – although it’s not colostrum provisioning.
Mother koalas produce a substance called pap, which is ingested by their newborns when they first begin to emerge from her pouch.
Pap is a euphemism for “feces.”
Baby koalas ingest their mother’s feces as newborns to inoculate their gut microbiomes with the correct tannin-busting bacteria that will eventually be required when the babies start to eat their diet of eucalyptus.
Pap has a higher water content and pH than mom’s normal feces, and it contains high levels of the desirable bacteria. So, what colostrum cannot accomplish, a little poop apparently will.
This post is an adapted excerpt from my book “Wild Moms: Motherhood in the Animal Kingdom“