Thandi, 34, lives at the National Elephant Center in Fellsmere, Fla. A technique being developed in Alabama uses blood tests to determine whether African elephants such as she are overweight. (Erik S. Lesser /European Pressphoto Agency)

African elephants in captivity are packing on the pounds, and experts warn that the rise in obesity is contributing to infertility, which could be detrimental to the survival of the species in zoos.

Just like humans, elephants with excess fat are more likely than others to develop heart disease, arthritis and infertility. Previous studies have shown an alarming number of African elephants in zoos have irregular or no ovarian cycles.

Elephants in the wild are threatened by habitat loss and by poaching prompted by the illegal trade in ivory. Zoos may be one of the few remaining ways to protect the species. But at U.S. zoos, which need to average about six births per year to maintain their population, the current rate is only about three per year. Obesity is suspected to be a major part of the problem.

The Lincoln Park Zoo in Chicago issued a report in 2011 predicting that if the abnormal ovarian cycles and resulting low birthrates continue, African elephants might disappear from zoos in the next 50 years.

To get a handle on the obesity problem, researchers in Alabama are looking for a better way to measure body fat on the animals.

Researchers are trying to find ways to measure their body composition so they can tell if they’re obese. (J Pat Carter/AP)

Elephants are so large that it’s difficult for zookeepers to tell the difference between a healthy-weight animal and an obese one. Zookeepers can weigh elephants, but there is no good method to determine whether most of their body weight is from muscle or from fat.

Kari Morfeld, an endocrinologist at the Wildlife Conservation Research Center at the Lincoln Children’s Zoo in Lincoln, Neb., recently came up with a unique way for determining the difference: comparing butt sizes.

Morfeld used a series of photos to rank elephants based on how much fat is around the backbone and hips. She used a scale of 1 to 5, with 1 being the skinniest elephants and 5 being the fattest. Most elephants in the wild are 2s, but Morfeld found that about 40 percent of zoo elephants are 5s. Her research was detailed in April in the journal PLOS One.

However, estimating obesity from images alone is very subjective, according to Daniella Chusyd, a graduate student at the University of Alabama at Birmingham.

Chusyd plans to measure obesity in a more precise way. Starting in the fall, she will collect blood samples from elephants in zoos across the country and compare the amount of lean tissue to fat tissue. She hopes the results of the study will have important implications for zoos and animal care.

“It may be that zoos will need to rethink how they house and feed elephants to reduce the incidence of overweight,” Chusyd said in a statement. “And not just elephants, as we hypothesize that a relationship between obesity, inflammation and infertility is present in many large mammals, including other imperiled African animals such as the rhinoceros and the gorilla.”

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