The Denver Zoo now specializes in the acquisition and study of elephant semen as a way to help save the Asian elephant. To further that mission, it houses six Asian elephants, a "bachelor herd" that consists of 53-year-old Groucho, 19-year-old Bodhi, 14-year-old Chuck and 13-year-old Jake. They're four of only six Asian elephants in the country trained for semen collection, although 9-year-old Duncan is in training. (Billy, the sixth elephant in the group, is not part of the process.)
"It takes a little while for the elephants to learn how to do it," says Maura Davis, curator of large mammals for the zoo. "It's a unique thing to train, but it's something we've become very proficient at."
Fewer than 40,000 Asian elephants exist in the world, and their population is in decline. So a decade ago, the Denver Zoo dedicated its ten-acre elephant terrain specifically to Asian elephants because "they were an endangered species, while African elephants were not classified as such until a couple of years ago," Davis explains.
"In the Denver Zoo’s history, we have housed mostly all Asian elephants," she says. "In the elephant community, there was a huge need for bull housing for Asian elephants. So we committed to helping with that need."
As the Denver Zoo was strategizing a new direction for its Asian elephants, it focused on becoming an all-male enclave.
"Part of what we were looking to do was, how do we continue to the overall success of elephants?" recalls Brian Aucone, senior vice president for Life Sciences. "One of those challenges was housing males."
Female elephants kick males out of their herd around the time they become teenagers, Aucone notes, "so we designed an entire facility to house male Asian elephants, and also committed to having those animals continue to contribute to the breeding program without necessarily having to move them to where females are or move the females here."
And so the Denver Zoo became an expert in elephant sperm collection, sending the samples to zoos with females ready for insemination.
To collect the semen, the bulls go through a process called rectal palpation — much like what male humans experience during prostate exams. Collecting elephant semen is usually a four-person effort, however, with one staffer feeding the elephant, two helping stimulate the bull by putting their arms in his rectum and massaging the prostate, and one prepared to collect the semen when the elephant ejaculates.
"A lot of elephants, when they move to Denver, are already comfortable with us doing things in that area," Davis notes, pointing out that elephants are trained at a young age to get enemas, which "is a huge part of their care if they were to get sick."
The staffers involved may need a little more education.
The process occurs behind closed doors, as the elephants back up to a gated area where zookeepers stand on a platform, ready to perform the procedure. One staffer stands before each animal, offering oranges and bananas and making sure everything is kept humane. "The whole time, everything in front of them is wide open," Davis says. "There's hay they can eat, but they're conditioned to back in and allow us to do the procedure, while the whole time they have the opportunity to leave."
The actual procedure lasts between three to seven minutes, depending on the elephant, but that's after thirty minutes of foreplay. "It starts with just getting comfortable with backing into the space and then getting comfortable with us touching their tail," Davis says. "So there's a lot of little steps that go into it, and we make sure they're comfortable with each step."
An elephant ejaculates up to 100 milliliters of liquid — less than half a can of soda — that contains billions of individual sperm. After the ejaculate is collected, the Denver Zoo's elephant team looks at the sample under a microscope to see how the sperm are moving. After that, semen is packaged up for other zoos across the country that hope to inseminate female Asian elephants.
The goal is to boost the diverse genetics of the species by having as many calves born from different fathers and mothers as possible.
"Preserving their genetics is important long-term," Davis says. "There are a lot of genetics being lost every time a male elephant passes away and hasn't had his samples taken from him."
However, the mission has its challenges. For starters, unlike human sperm, elephant sperm don't freeze well. "We don't really know why," Davis says. "We're trying to understand the morphology of Asian elephant sperm a bit to design a study. It really takes a lot of medical knowledge to be able to do that. We have discussed how we get more information from all this, but there isn't a set reason right now why Asian elephant sperm is difficult to freeze. We just know that it is."
While natural breeding, in which a male and a female elephant are paired up, is often "hugely successful," Davis says, it's much harder to ship a whole elephant than it is to send its semen.
So the Denver Zoo packages the semen in a container with a 36-day extender, which is nutrition to keep the sperm alive, and ships it through FedEx, Southwest Cargo or a private courier. "But sometimes they get hung up or lost for a couple of days and might not make it in time for the female's cycle, or the semen will die over that amount of time if they don’t make it overnight when they are supposed to," Davis acknowledges.
And even when the sperm samples are moved quickly and arrive at their destination fresh, insemination is often unsuccessful. Since the Denver Zoo sent out its first sample in 2018, there's only been one official birth that resulted: a female elephant calf born in Houston who is Bodhi's daughter.
The results of many other efforts are still unknown; female elephants stay in gestation for two years. "Artificial insemination is still not a perfect science, and there are a ton of factors that go into a successful calf coming from it," Davis notes. Among other things, "females only cycle for about 36 hours, so you need to time it perfectly. Collecting from the males is difficult, so you need to have a great sample that gets extended perfectly and shipped and arrives in absolutely great condition.
"Once all of those factors work out and you get the sample there — in great condition, at the perfect time — it then needs to take," Davis explains. "Just like with humans, some elephants have a more difficult time getting pregnant and staying pregnant."
The goal is to boost the diverse genetics of the species by having as many calves born from different fathers and mothers as possible.
"Preserving their genetics is important long-term," Davis says. "There are a lot of genetics being lost every time a male elephant passes away and hasn't had his samples taken from him."
However, the mission has its challenges. For starters, unlike human sperm, elephant sperm don't freeze well. "We don't really know why," Davis says. "We're trying to understand the morphology of Asian elephant sperm a bit to design a study. It really takes a lot of medical knowledge to be able to do that. We have discussed how we get more information from all this, but there isn't a set reason right now why Asian elephant sperm is difficult to freeze. We just know that it is."
While natural breeding, in which a male and a female elephant are paired up, is often "hugely successful," Davis says, it's much harder to ship a whole elephant than it is to send its semen.
So the Denver Zoo packages the semen in a container with a 36-day extender, which is nutrition to keep the sperm alive, and ships it through FedEx, Southwest Cargo or a private courier. "But sometimes they get hung up or lost for a couple of days and might not make it in time for the female's cycle, or the semen will die over that amount of time if they don’t make it overnight when they are supposed to," Davis acknowledges.
And even when the sperm samples are moved quickly and arrive at their destination fresh, insemination is often unsuccessful. Since the Denver Zoo sent out its first sample in 2018, there's only been one official birth that resulted: a female elephant calf born in Houston who is Bodhi's daughter.
The results of many other efforts are still unknown; female elephants stay in gestation for two years. "Artificial insemination is still not a perfect science, and there are a ton of factors that go into a successful calf coming from it," Davis notes. Among other things, "females only cycle for about 36 hours, so you need to time it perfectly. Collecting from the males is difficult, so you need to have a great sample that gets extended perfectly and shipped and arrives in absolutely great condition.
"Once all of those factors work out and you get the sample there — in great condition, at the perfect time — it then needs to take," Davis explains. "Just like with humans, some elephants have a more difficult time getting pregnant and staying pregnant."
The Denver Zoo covers the cost of shipping the samples, and makes no profit off the semen it sends. Instead, it prefers to "work cooperatively" with other zoos "versus viewing it as a competition," Aucone says.
"Dedicating ourselves to male elephants, this is kind of our role in the community, so in order to help the breeding population, we incur the cost of the semen collection and processing," Davis notes. "The institution, if they get pregnant, incurs the cost of raising the calf to adulthood.
"For the continued sustainability of the population, I think all of us work really well collaboratively," he says. "It's a nice way for us to be able to spread out the genetics across the country."
