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Orphaned elephants need milk. These baby-mother pairs might have the formula.

Elephant keepers Mistley Bennett, left, and Mindy Albright milk Umngani at the San Diego Zoo Safari Park. (Tammy Spratt/San Diego Zoo Global)

SAN DIEGO — On a chilly, breezy morning at the San Diego Zoo Safari Park, an African elephant named Umngani was ready to nurse her hungry calf, Mkhaya.

But first her keepers needed Umngani to cooperate in a research project meant to unlock the secrets of a life-giving substance: mother’s milk. At stake was not just Mkhaya’s eager tummy but also the health and survival of orphan calves in elephant sanctuaries in Africa and zoos around the world.

Umngani’s trainers used hand signals, sweet words, and a bucket of sliced lettuce, cucumbers, carrots and yams to coax the 7,330-pound animal to the edge of a small holding area. Umngani, age 30, knew the drill.

“Lean in,” keeper Mistley Bennett told her softly. Umngani extended one giant front foot toward the iron bars that always separate keepers from the park’s 14 elephants.

Mindy Albright, the lead elephant keeper, reached through and gently began “expressing” one of Umngani’s nipples. Milk squirted into a small, sterile cup. A third keeper comforted 6-month-old Mkhaya, who waited nearby, impatient to nurse.

It’s well known that milk helps newborn mammals survive and prosper. But just why that is true remains a puzzle for scientists, even those who specialize in milk, lactation and infant growth. So when Umngani and her sister Ndulamitsi gave birth last year and began nursing their calves, the zoo decided it was time to launch a milk project.

The goal is to find the right ingredients for an improved milk replacement for orphaned elephant calves — some of whose mothers are among the 20,000 or so African elephants killed by poachers each year — or calves whose mothers cannot or will not provide milk. Substitutes are already in use, but the researchers hope to help develop products that can be tailored to calves’ age, development and gender. Baby elephants drink milk for the first three years of their lives.

A better understanding of milk’s nutritional composition “is integral to increasing survival of young calves in these [perilous] situations,” said Katie Kerr, nutritionist for San Diego Zoo Global.

The milk will be analyzed by zoo staff and milk researchers at the University of California at San Diego and the Smithsonian’s National Zoo milk repository. The project is being watched closely by staff at the Reteti Elephant Sanctuary in northern Kenya, where 15 calves are struggling to grow healthy enough to return to the wild.

Researchers do not expect their task to be quick or easy — some say it may take two years. Among other variables, a mother’s milk changes as her baby grows, and researchers need to understand that process.

“Not a lot is known about human milk and even less about other species',” said Lars Bode, associate professor of pediatrics at UCSD and past president of the International Society for Research in Human Milk and Lactation. He said he became interested in Umngani and Ndulamitsi when he and his staff were on an outing to the Safari Park.

Two or three times a week, Albright expresses milk from the two mother elephants. The goal is to get five milliliters per week from each elephant, or just over a teaspoon.

The first few drops of milk are watery and almost clear. Then the milk begins to have a higher fat content. The process is meant to be gentle but quick — a minute or two.

Albright pulled gently with gloved hands. “We’re still trying to perfect our technique, but each cow is different,” she said. “It’s really exciting stuff.”

Umngani is placid and takes to the procedure easily. Ndulamitsi is more tentative and is suspicious of anyone other than her keepers. The milking is done in an area off-limits to the public.

The samples are stored at subfreezing temperatures at the park laboratory. When the zoo has six months’ worth, researchers will begin examining it for proteins, fat, amino acids and other nutrients.

Michael Power, animal scientist at the Smithsonian repository, is enthusiastic about the project but also cautious about what it will yield.

“We’re getting an exploding amount of knowledge about the proteins, sugars, all the different things we now see in milk” of various species, he said. “But that is far outstripping our ability to understand their functions.”

The repository — with 15,000 samples from more than 200 species — has studied elephant milk in the past. It has about 120 Asian elephant milk samples and 50 samples from African elephants. Most of the African samples were from cows whose calves were already a year old, making it difficult to determine whether younger calves might need a different formula.

But with new research techniques and the promise of multiple longitudinal samples from two cows, the San Diego project is bright with possibilities, Power said.

“This milk will be looked at completely,” Power said.

Power said he hopes to learn more about the nutrient composition of African elephant milk, how it changes over time and how milk differs among elephant cows.

When a zoo newborn cannot be nourished by its mother’s milk, keepers scramble to find a substitute. This happened with the 2017 arrival of a premature baby hippo at the Cincinnati Zoo & Botanical Garden, which then sent hippo milk to the National Zoo for analysis.

Finding the right replacement, along with other treatments, “was trial and effort for several months,” said Barbara Henry, the zoo nutritionist. In the end, Fiona the hippo survived and went on to become a superstar.

At African sanctuaries, the plight of motherless elephant calves can be dire.

The Reteti sanctuary, in collaboration with San Diego Zoo Global, offers a haven for elephants injured by the ravages of drought and disease or by the poaching of hunters seeking to cull their tusks. Some calves at the facility have lost their mothers, and some have mothers who are not able to nurse.

Stephen Chege, a veterinarian at Reteti, is now a postdoctoral fellow with the San Diego Zoo. He has seen the results when Reteti keepers try to find a milk substitute.

“Sometimes we get it wrong, and we get cases of diarrhea,” Chege said. Constipation can also occur, Power said. Either can be debilitating.

Grober Nutrition, a New York-based company that sells milk replacements for wild animals, has formulas for Asian and African elephants. The Asian formulation is rooted in a 2012 study led by the Smithsonian, and the African one grew out of two more-limited studies by researchers in South Africa, said Merritt Drewery, Grober’s nutrition, quality and research supervisor.

“I feel much more confident about our Asian formulation than our African formulation,” said Drewery, adding that she looks forward to the San Diego project’s results. “There is a [knowledge] gap to be filled.”

At the safari park, keepers say Umngani and Ndulamitsi’s participation in the research has been helped by two factors: their intelligence and their large mammaries, each one about the size of a honeydew melon.

(As a side goal, the researchers would like to develop a breast pump for elephants. In university labs, researchers even have breast pumps for mice.)

Some weeks it can take two or three sessions to get the five milliliters. But this winter morning went well. Umngani chewed her treats and seemed to relax as Albright squeezed and pulled. Mkhaya, meanwhile, grew restless.

“Like human babies, elephant babies have a short attention span,” Albright said.

When the milking was over, Umngani turned to her primary job: feeding Mkhaya.

Albright, satisfied, praised the mother. “Good girl,” she said.

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