"Weighty Matters" by Suzanne Hall, San Diego Zoo Blogs
These days, Bai Yun is weighing in at about 214 pounds (97 kilograms). This seems about where we might expect her to be at this time, more than half way through rearing her cub, Zhen Zhen. As an adult female panda, we have seen Bai Yun’s weight fluctuate from 205 to 231 pounds (93 to 105 kilograms) routinely, depending on where she is in her reproductive cycle.
Before she gives birth, Bai Yun spends several months as an independent panda. She has time to focus on putting on weight, and she feeds and rests her way to the top of that weight range. By the time a birth is weeks away, she is large enough to begin her prepartum fast with some comfort.
When a cub is born, she fasts a bit longer, but now has the added caloric drain of lactating to support her infant. Bears produce high fat, low carbohydrate milk, aiding in rapid growth of their youngsters. Despite fasting, they are able to maintain most of their muscle mass throughout the process. It’s an amazing adaptation, and cold-weather bears can sustain lactation without food or water intake for several months.
As lactation continues, Bai Yun loses weight slowly. Her fat stores are depleted by milk production. Studies show that in mammals, a female is drawing nutrients from her bones to sustain the nutritive nurturing of her infant. By the end of the mother-cub association period, a female’s bones may be lighter as a result. We have found that after 18 months of caring for her cub, Bai Yun’s weight will drop to about 209 pounds (95 kilograms) or lower. Her body is greatly changed from the pre-birth interval.
It can take several months for her to gain weight again. Estrus is also a physiologically demanding time for Bai Yun, as she eats less and is more active when close to peak estrus. However, in the six months between weaning and giving birth again she is able to prepare to again meet the energetic requirements of rearing a cub.
Gao Gao has been maintaining his weight at about 168 to 174 pounds (76 to 79 kilograms). His weight fluctuates a bit due to preferences in bamboo, activity level changes due to enrichment, or other factors. He has always been lighter than Bai Yun. But watch out, Gao Gao…your daughter Su Lin is closing in on you: she has been weighed between 161 and 165 pounds (73 and 75 kilograms) in the last week!
For those keeping track, “little” Zhen Zhen is now closing in on 46 pounds (21 kilograms). Gao Gao can breathe easy knowing his youngest needs another couple of years before overtaking him on the scales!
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