Giant pandas have the smallest babies relative to size of all placental mammals (like us). And not only do the cubs weigh nearly a thousand times less than their moms, they’re also blind, deaf, and mostly naked. These wee cubs depend on their mother’s milk for a lot longer than most, and during that time, panda milk goes through dramatic changes: from protein-rich "first milk" that's chock full of antibodies to low-lactose “mature milk” about 20 to 30 days later. The findings were published in Royal Society Open Science this week.
In captivity, lactation and nursing in giant pandas (Ailuropoda melanoleuca) typically lasts about nine months, though cubs have been known to suckle for two and a half years. On the opposite end of the placental mammal spectrum are British grey seal moms, which start producing mature milk in as little as 24 hours. (Meanwhile, marsupials like kangaroos give birth to such immature babies, some describe it as “external gestation.”)
“Bear cubs are born at an extremely early stage of development,” University of Glasgow’s Malcolm Kennedy explained in a statement. “Bear milk may contain unique factors on which cubs depend for relatively prolonged periods for immune protection, gut microbiome health, and other physiological development.” After all, pandas must eventually move from milk to a mostly vegetarian diet – despite having the digestive system of a carnivore.
Kennedy and colleagues collected milk from six captive-bred pandas at the Chengdu Research Base of Giant Panda Breeding in China between 2006 and 2012. These samples ranged from 12 hours after birth to five months into lactation. They tracked the proteins, sugars and other molecules to better understand how the components of first milk change over time and how long the transition to mature milk takes. The team also gathered samples from a bottlenose dolphin, Indian elephant, African bush elephant, polar bear, grizzly bear, cow, dog and a woman from Scotland.
Giant panda milk, they found, contains proteins and other molecules that change more slowly from first milk to mature milk than any other placental mammal. And anti-bacterial defenses are central to this transition.
After a panda cub is born, mom’s milk has an abundance of immunoglobulins (or antibodies), which are essential for the newborn’s natural defenses against infections and control its gut microbiome. These proteins diminish over time and others appear, including some that help transfer essential lipids and others that help digest milk fat or curdle milk into a semi-solid form. The team also observed dramatic changes in complex sugars: Some that help with the immune system taper off after about a month, while the concentration of others that prevent bacterial colonization of the gut begins to increase.
“One important implication of the work is that panda milk is complicated and that zoos should make more effort to ensure that panda mothers can behave as naturally as possible,” Kennedy told IFLScience, “so that they can rear their cubs without the need for the use of artificial milks.”
Image in the text: A newborn giant panda cub inside an incubator at the Chimelong Safari Park in Guangzhou, China. plavevski/Shutterstock
[H/T: Science News]