Inter-Species Nursing - Milk Week


By Tanya Silverman

Photo courtesy of Wikimedia Commons.

Adorable animal videos are everywhere online. One popular offshoot of this mega-genre features inter-species nursing. If you like to unwind by watching clips of cute creatures, perhaps you have come across videos of mother cats adopting red pandas or dogs tending wild boars. Beyond the heartwarming nature of such segments, is inter-species feeding actually beneficial for the baby mammals?

“When when you swap infants from mothers of different species, you’re really depriving those young of critically important constituents they need to be getting from mother’s milk to optimize their growth and development,” says Katie Hinde of Harvard’s Evolutionary Biology Department.

Hinde, an Assistant Professor who maintains the research blog, “Mammals Suck… Milk!”, explains that each mother’s milk “is composed of a combination of nutrients, hormones, amino factors, bacteria,” all of which are “quite important for orchestrating physiological, neurological, behavioral and microbiological development” when ingested by the infant. Acknowledging the complex composition of mothers’ milk, what comes from the one species may not be sufficient for baby animals of another.

When similar species nurse off each other, however, Hinde explains that there is “greater likelihood that their milk is going to be matching.”

To reference a cute animal video, there was a case in 2010 when a house cat mom adopted abandoned baby bobcats – the cross-cat circumstance may suffice because the domestic cat’s milk could match most components of what a bobcat mother produces.

Hinde points out that the differences in the body sizes, however, may cause issues because even if the the domestic feline female supplies milk of proper composition for the young, she “might run out of the body reserve needed to to keep making that milk for as long as bobcat mothers may be able to nurse them in the wild.”

There are also cases of female humans breastfeeding monkeys in certain parts of the world.

“In general, human milk is similar to the milk of monkeys and apes,” she says, but adds that people lactate less fat and less protein, which may lead to complications.

Other mammals’ milk may have radically different components. Bruce Patterson, curator of mammals at the Field Museum who studies evolutionary biology, exemplifies baby seals, which develop very rapidly. Seal milk, therefore, has “amazing fat concentrations” of about 25 percent. Katie Hinde also cites baby seals in how they “need particular fats [from milk] to support the growth of their blubber layers.”

Sustaining baby seals with something like cow’s milk or goat’s milk would likely not meet their physiological requirements, Patterson explains.

While the imagery of a calf or kid feeding off a mother seal seems unlikely, there are some interesting tertiary occurrences, such as an instance where a mother cat adopts a baby squirrel. She allows the squirrel to live with her litter, letting the rodent breast-feed and catnap amongst her natural offspring. At the end of the video, viewers can watch heartwarming footage of the squirrel purring just like a kitten.

That may be sweet and all, but some of us may ponder, is cat milk healthy for a squirrel? If you think about it, they are not so closely related, plus cats are carnivorous, while squirrels are mainly vegetarian.

Hinde says that it’s not unreasonable to speculate that cat milk may be incompatible, citing a recent paper by Amy Skiebiel and colleagues where these scientists found that the “protein and fat content” in carnivores’ milk “seemed to be much higher” than plant-eaters.

For mammalian dietary consideration, Hinde reasons that there are probably more problems in trying to raise carnivorous youth off of herbivore milk than vice versa, as meat-eating mammals have “really high nutritional requirements” which milk from herbivores may not be able to satisfy.

Overall, Hinde explains there is no “iron-clad rule” as to whether inter-species feeding is wholly beneficial or detrimental to young.

“We still don’t know everything about what any single-species milk looks like, what’s in it, how it gets there, how long the infant needs to consume it, what it does when it’s inside the infant,” says Hinde. “These are still fundamentally unanswered questions among mammals, so it’s not clear how much switching litters between mothers across species may disrupt important aspects of mother’s milk that they need to be getting from their own species.”

Hinde also points out that these inter-species nursing segments can only show us something static in time, as they do not provide information on whether it’s an continuous occurrence, or merely something performed occasionally or for an audience. Whether these instances indicate actual adoption or replacement is not clear – no matter how cute we think these videos are.