Amazing Mammal Mothers Making Milk

You may have heard someone say that breastfeeding our babies is a basic human right. However, it isn't uniquely human. In fact, we share breastfeeding with non-human mammals—cats, cows, and capybara, to name a few. In fact, the term mammal comes from the word mammalis, which is of Latin origin and means "from the breast." Mammals share many features, such as warm-bloodedness, hair, a four-chambered heart, as well as feeding of the infant with milk from the mammary glands.

Does breastfeeding in humans have any similarity to breastfeeding in other mammals? As a zoologist and former zookeeper, I've often been struck by the similarities of mothering among mammals, a very diverse group in many other respects. I've seen giraffe, camels, antelope, gazelles, kangaroos, babirusa, zebras, elephants, and lemurs nurse their own and, sometimes, their close relatives' infants. The basic act of nursing is very similar to our own, mechanically speaking. Of course, the biggest similarity is that we all, humans and non-humans, are evolutionarily and biologically built for the job! What else do we share with these non-human mothers? Consider some aspects of breastfeeding in the human condition and how these compare with other mammals' parenting practices.

I'm Thirsty
For me, there is nothing as strong as that sudden desire for water that I feel when I first sit down and feed my baby. While nursing, I feel like I need to consume about twice as much water as I would when I am not breastfeeding, especially when out in the heat or being physically active. As a zookeeper working out in the hot sun, sometimes it felt like I couldn't possibly take in enough water to quench my thirst between pumping sessions, and I'd joke with the zoo's veterinarians about hooking me up to IV fluids. Of course, being a little thirstier than usual isn't only a human thing. Being thirsty can even change an animal's natural behaviors, as seen in the Grevy's zebra and Somali wild ass.

The Somali wild ass and the Grevy's zebra are both tough animals from the Horn of Africa, found in Kenya, Somalia, Eritrea, and Ethiopia. They are Equids, which means they are related to horses, but they've both become specialists in their desert lifestyle. They can eat very unpalatable and dry vegetation—coarse brush, sedges, and thorny plants that domestic goats, cows, and even camels avoid. Adults of both species have adapted to have very low water requirements and can go up to five days without drinking. Naturally, lactating females are different. Lactating Somali wild ass females need to drink every day, while Grevy's zebra females need to drink at least every other day. During lactation, females of both species have a smaller range which allows them to stay closer to water sources. For Equids and for us, the behavior is similar: keep a water source nearby and drink to thirst.

What a Big Baby!
The blue whale is the largest animal alive—adults can be 75-100 feet long and weigh more than 150 tons, the weight of almost 4 semi-trucks with full loads. Baby blue whales have to coordinate breastfeeding with surfacing to breathe and are one of the few species that have to learn to do something before they can breastfeed. A mother blue whale will guide her newly-born offspring up to the surface to catch its first breath before going underwater again to nurse. Babies will consume up to 50 gallons of milk a day, which is of toothpaste consistency and 35-50% fat. All of this fat is needed, of course, because a baby gains around 10 lbs an hour and about 250 lbs—about as much as LeBron James, professional basketball player—in a day.

Some mothers can really relate to a quickly gaining baby. My own son, for instance, never lost weight in the hospital, was always in the 99% for weight, and as a preschooler currently dwarfs many second graders. It's important to realize that all babies grow at different rates and that quickly growing breastfed babies aren't overweight; they are just following their own growth pattern, which is frequently genetic. This can be reassuring to know when your in-laws start making comments about your own big (or petite, for that matter) baby.

Leaky Milk
How does a mammal so primitive that it lacks nipples still feed its baby? The platypus, an egg-laying mammal from Australia, has so many quirky characteristics that the first specimen brought to Europe was considered a hoax. This funny looking mammal not only has flipper feet, a beaver-like tail, and a duck-shaped bill, but it is also one of the few mammals that is venomous. The way in which she feeds her infant is also a unique characteristic. Since the platypus does not have nipples, she secretes milk from her mammary glands onto her skin and her offspring lap up the milk on her chest as she reclines in her den.

Some mothers leak a little milk now and then. Other mothers never leak any milk. Then there are the mothers who wake up to a soaking wet sheet in the morning, due to milk leakage overnight. These moms also carry plenty of breast pads and an extra shirt in their diaper bag, just in case. Leaking milk isn't fun, but when it happens to us, we can remember the platypus and her soggy feeding condition.

Your Older Nursling
Let's face it—some folks in our society today frown on nursing a baby older than 12 months, the minimum duration recommended by the American Academy of Pediatrics. Many women with older nurslings breastfeed "in the closet"—secretly at home without their friends', pediatrician's, or in-laws' knowledge. Some feel embarrassed or ashamed to still be nursing. Even those who don't feel embarrassed may just shy away from revealing the fact that their toddler (or preschooler) is nursing in order to avoid receiving well meaning advice or being in conflict with others who have chosen a different parenting path. A common but mistaken idea in our society is that breastfeeding should be over by the baby's first birthday. As a friend of mine once said to her pediatrician, "Why is breastfeeding so great for the first 365 days, but on day 366, it suddenly isn't okay anymore?"

Let’s consider the nursing habits of some of our closest primate relatives. The chimpanzee, gorilla, and orangutan all share more than 95% of our DNA. Their parenting styles are very similar to ours—they carry their infants continually and nurse on demand. The weaning age of a chimpanzee is around 48 months, a gorilla will nurse until 52 months, and a Borneo orangutan will nurse on average 42 months, and may continue to nurse for as long as 5-7 years! These apes all have a longer average breastfeeding period than industrialized human societies today, despite the fact that human infants are born less developed than any of the apes, are less self-sufficient for longer, and have a longer infancy. The typical nursing period in pastoral societies in developing countries is much nearer the durations seen in the apes. It's time that we forget about the 12-month weaning recommendation and go with the flow.

Gotta Go?
The okapi is a secretive creature related to a giraffe, which is found in the rainforests of the Democratic Republic of the Congo. It has a neck somewhat shorter than a giraffe and is dark brown, except for having white stripes on its rear end. As a zookeeper, I've had the pleasure of watching several okapi being born. Before our first okapi was born, we prepared for the birth of these unique animals by doing some research. We discovered that the newborn okapi does not defecate for up to a month after birth because it uses its mother's milk so efficiently. This may have been an evolutionary advantage because okapi babies do not follow their mothers, but remain in hiding, where defecation might alert a predator to their presence. Some of the first okapi babies born in zoos were treated by vet staff for constipation when, in fact, this stooling pattern was a normal phenomenon.

Of course, breastfed human babies do not follow the okapi pattern of defecation. However, sometimes breastfed babies over a month do not defecate as frequently as a health care professional would expect. A mother may be fearful that her baby is constipated. An older baby may defecate once daily. Some babies have been reported to defecate every few days or even once every five days or longer. Whether there is a reason for this defecation pattern compared to more frequently stooling breastfed babies isn't entirely clear. Generally, as long as the baby is gaining well, feeding normally, and is otherwise healthy, it's considered a normal variation to have a longer stretch between bowel movements. Also, it's important to realize that consistency of stool, rather than frequency, determines constipation, which is rare in breastfed babies. When a baby is constipated, his stool is hard in consistency, a far cry from the soft, mustardy-seeded stools typical of the breastfed baby.

He's Constantly Nursing!
My second born, the big boy, was also one of those babies who wanted to nurse very frequently. Especially at the beginning, it seemed like I'd scarcely settle him down and he'd want to be up and attached again. He'd sleep in a wrap in my arms, always just a wiggle away from another snack. I've commiserated with other moms about similar nurslings—those who just want to be attached to mom nearly 24/7.

When we have a baby with this nursing pattern, it may remind us of the kangaroo. A kangaroo joey is very immature at birth, compared to other mammals. At the size of a lima bean and the look of a fetus, it crawls up its mother's body and attaches to her nipple. And there it remains, continuously attached inside her pouch. Her nipple swells in the baby's mouth so that the baby will stay permanently attached during the first stages of lactation. In fact, the kangaroo newborn doesn't even have the ability to detach and reattach herself; if she unlatches before she's developmentally ready, she could die. As she develops, she will gain fur and her eyes will develop. Eventually, the baby will cease her continuous nursing and begin to stick her head out of the pouch. Later, she will climb out of the pouch to explore but will go back in when she needs comfort, a safe place to go, or a meal. Finally, she may be too large to return to the pouch but may continue to nurse by putting her head back inside the pouch. Our continuously nursing newborns? They'll grow out of it, too.

Health Consequences of Bottlefeeding
There are many reasons why women may resort to formula feeding, even when they are aware of the health risks associated with it. Frequently, this is a very complicated and challenging decision-making process. Wild mammals do not have infant feeding choices to make. If the mother is unable to produce enough milk, becomes separated from her young, or is eaten by a predator, infants not at or near weaning age will typically die. Some primates and a few other mammals, such as elephants, will occasionally feed orphaned infants, especially ones they are related to, with their own milk. There are even a few cases of cross-species milk sharing (if you're interested, do a Google search on interspecies nursing), but they are striking because they are not the norm. Also, since milk is species-specific, cross-fostered babies do not always survive or have the best of health.

Non-human, bottle-fed mammals do exist on farms, in sanctuaries or zoos. I've been lucky to watch many young mammals feeding from their mothers (or sometimes aunties, if mother doesn't happen to be nearby). There are rare cases when a newborn has to be hand-reared with a bottle--if the mother dies or becomes too ill to care for her youngster. Hand-reared young mammals can be less robust when compared to their mother-reared counterparts. They may be smaller and have more health problems, such as diarrhea. While adequate milk replacers have allowed us to save the lives of these young animals, rarely do they enjoy great health. Also, the bonding and natural behaviors they learn while nursing from their mothers seem to help them prepare for parenthood, themselves. This may be why hand-reared female mammals do not always have the skills to raise their own babies. Hand rearing in zoos and sanctuaries is now done sparingly, with a trend towards keeping the offspring with other members of the same species which may, in turn, allow the hand-reared baby a better chance of parenting her own offspring. I can't help drawing a parallel to our own society. When our young people grow up around nursing babies, when society sees nursing as a norm, and when our own mothers have nursed us, breastfeeding may come more easily for us, as well.


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Rosalie now lives in Grand County, in rural Colorado. She has a MS in Zoology, and worked as a Zookeeper for 9 years. She currently works part time in the medical field, and parents her 3 children, including a 5 month-old nursling.