Mammals & Milk

When it comes to normalizing breastfeeding we often use the most basic point - we are mammals and mammals make milk for their babies. (We wrote a whole post about it here!). But would you believe that some mammals make 16 pounds of milk daily for their young or that some have 9 nipples and release their milk in 1 minute spurts? How about a mammal that nurses her baby for years and tandem nurses with their older babes and newborns - just like humans can? The patterns of nursing mammals are fascinating and we’re sharing some of the coolest lactating mammals out there!



First up, seals! Seals (and whales) make some of the fattiest milk out there largely in part to protect their young from the ice cold waters in which they’re born. Gray seals have milk that is over 50% fat and hooded seals have milk that is over 60% fat (compared to human milk which is about 3 to 5% fat this is a ton!) and all of this fat fuels the rapid physical growth and thick layer of  protective blubber, doubling their weight in about four days (1,2)! Additionally, hooded seal moms only nurse their pups for four days and this is because they’re forced to move into the freezing waters shortly after birth and have a very small window to give their pups the protection they’ll need to survive the cold. So while four days seems short, they’re giving their pup over 16 lbs of seal milk every day during this period. Amazing! 

 © Photography by Luciano Candisani, Minden Pictures, National Geographic Creative 

© Photography by Luciano Candisani, Minden Pictures, National Geographic Creative 



Who needs nipples?

The duck-billed platypus is an egg-laying mammal. After the eggs hatch, the young will rub against the mom’s stomach where she has two patches of mammary glands underneath her fur (3). The babies stimulate a milk let down (milk release) by moving around the small hairs on the mom’s stomach (similar to how a human baby suckles at the breast to trigger the milk release) and the milk is released from the mom’s nipple-less glands. Baby platypus are nursed for 4-5 months where they are kept inside the burrow for protection before venturing off into the world on their own (4).



 Image retrieved from  Zooborns .

Image retrieved from Zooborns.

Aside from being insanely cute, baby orangutans nurse exclusively for the first year and start receiving solids around 12-18 months (5). They go on to nurse for 6 to 8 years until weaned - wow! Now this might seem like an eternity but it really highlights how essential a mother's milk is for survival among mammals. Orangutans are raised in environments that are unstable and unpredictable with limited nutritional resources, if they relied on their surrounding foods, they would not survive as a species. So mama orangutan's fill in this nutritional need by continuing to nurse their baby for survival. Basically, I think we can all agree, mama orangutans are superheroes! 

 Image retrieved from  Wikipedia

Image retrieved from Wikipedia


Bears are incredible mammals. Their reproductive and lactation abilities (spoiler alert: they mate in spring but can delay pregnancy until fall by delaying the fertilized egg to implant in the uterus - what?! (6). Because they're able to delay pregnancy, this means bear cubs are born in winter when mama is hibernating. Bears have a short pregnancy relative to humans and bear cubs are born even more immature than human babies, they cannot open their eyes and basically they're only ability is suckling (6). Winter hibernation allows mama bear to nurse her cubs for about 5 months so they can be strong enough to brave the world in spring (6). Meanwhile, mama bear has no access to nutritional resources so she is making milk and feeding baby off her fat stores which is pretty remarkable and while we are talking about bears, this shows us a glimpse into how women in extreme conditions can breastfeed. As with all mammals, bear milk will change as the cubs grow and guess what, cubs have growth spurts and increased feeding too (sound familiar?). Baby cubs will continue nursing for a few years as they grow and develop (6). And our last cool fact about bears, mama bear has 6 nipples and cubs will change which nipples they nurse on depending on their age - younger cubs will nurse on the lower nipples while older cubs nurse on the higher nipples and mama bear can control which nipples release milk (6). 



 Image retrieved from  TripAdvisor

Image retrieved from TripAdvisor

Any tandem nursing moms reading this? Like, bears, baby marsupials are born immature (after only 28 days of pregnancy!) and rely exclusively on mom's milk to grow (7). In the first few months they stay cozied up in mom's pouch nursing on nipples inside the pouch (7). Just before baby is ready to leave the pouch, mom's milk supply will dramatically increase almost like prepping for a major growth spurt and the baby will nurse for about a year until weaned (7). Once the babe leaves the pouch, mama is ready for the next one! Whew! Marsupials like the wallaby have a fast reproduction rate so in order to keep up and provide sufficient nutrition for their young, they nurse both the new joey and the older sibling (7, 8). Perhaps even cooler, mama will develop a new nipple that is meant just for the new little one and provides a fattier milk for the newborn allowing her to nurse both of her young and provide unique compositions of milk to each offspring (7). 



(1) Bremel, R. (1995). Milk Composition - Species Table. Retrieved from

(2) Oftedal, O. et al. (1988). The composition of hooded seal (Cystophora cristata) milk: an adaptation for postnatal fattening. Canadian Journal of Zoology, 66(2), 318-322.

(3) Divljan, A. (2015). Animal species: Platypus, Ornithorhynchus anatinus. Retrieved from

(4) Enjapoori, A. (2014). Monotreme lactation protein is highly expressed in monotreme milk and provides antimicrobial protection. Genome Biology and Evolution, 10(6), 2754-2773.

(5) Smith, T. et al. (2017). Cyclical nursing patterns in wild orangutans. Science Advances, 5(3), 1-9

(6) Alaska Department of Fish and Game. (2007). Bear Milk. Retrieved from

(7) Nicholas, K. et al. (1997). The Tammar wallaby: a model to study putative autocrine-induced changes in milk composition. Journal of Mammary Gland Biology and Neoplasia, 3(2), 299-310.

(8) Lawrence, R. & Lawrence, R. (2015). Breastfeeding: A guide for the medical professional. NYElsevier Health Sciences.