More of Dr. Ellen Bronson's patients are developing the afflictions typical of old age, including arthritis, failing eyesight, muscle atrophy, kidney problems, flagging appetite, cancer and bad teeth.
The problem is that none of her patients can tell her where it hurts. Some are too big for her examining table, and others might prefer to eat her.
Bronson, 39, is the head veterinarian at the Maryland Zoo in Baltimore, and as better husbandry and veterinary care lengthen the life spans of animals in captivity, she and her counterparts around the country are spending more time on geriatric care. Just as medical science has allowed humans to live longer, the same advances are being applied to animals in captivity, which now live far beyond their life expectancy in the wild.
Aging animals, birds and fish in zoos and aquariums today are on special diets; they're receiving physical therapy, drugs for kidney failure and arthritis, antibiotics for gum disease, CAT scans and MRIs, and even chemotherapy for cancer. Some get better medical care than many humans.
"There is no hard data, but we do feel, over the last couple of decades, we do see more geriatric animals," she said. Veterinarians are adapting advances in human medicine and clinical technology to the challenge, "and we're getting better at what we do."
On a recent morning at the zoo, three employees hoist a 132-pound African leopard named Hobbes onto Bronson's exam table in the zoo's new, $200,000 Huldah Lieberman X-ray Suite.
Hobbes is nearly 17 years old, a codger among leopards, which typically live 15 to 20 years in captivity. Abandoned as a cub, he was brought to Baltimore in 1996, along with another orphan, a female named Amari, now 18.
Knocked out with an injection a half-hour earlier, Hobbes lies on the table, eyes closed and motionless except for the slow rise and fall of his abdomen. There's a plastic breathing tube in his airway delivering oxygen and anesthesia. A sensor clipped to his pink tongue sends heart rate and blood oxygen data to a beeping monitor.
As her assistants begin looking for veins to insert IV lines for fluids and drugs, zoo veterinarian Dr. Allison Wack quickly begins a hands-on examination. She manipulates Hobbes' hind legs and feels through his lush, spotted fur for growths, and along his spine and craggy hip bones.
X-rays during his last exam, in 2009, revealed a collapsed disk in his spine, and evidence of arthritis as the two adjoining vertebrae began to rub together and form calcium deposits at the joint.
"It was suspected from the way he walks, a little stiff in the rear," Bronson said. It was also clear that Hobbes was losing muscle mass in his hindquarters, perhaps because of reduced movement.
"He does have muscle atrophy, but I don't think it's any worse" than in 2009, Bronson declared.
Spinal arthritis can also lead to neurological problems and difficulty walking — the sort of decline that would quickly bring death in the wild. But "so far we've seen no neurological deficits."
Hobbes was placed on a regimen of glucosamine and chondroitin — the same joint supplements taken by many humans with arthritis. He's even been trained to put his front feet up and stretch his back and hips on command, part of his physical therapy.
"It helps a lot to keep him mobile," Bronson said. He's still able to climb a tree in his enclosure, and jump over a rock wall.
The zoo's staff is also providing arthritis care to Alaska, a 23-year-old polar bear (also being treated for kidney failure); Fifi, a penguin, 28; Joyce the chimp, 39; a red-ruff lemur; and a 13-year-old steer and a 14-year-old goat in the zoo's farmyard.
Zoo animals have always grown old and sick, said Mike McClure, the zoo's general curator.
"Now we actually do an improved and better job of taking care of the older animals. There are more medical options available to us. There's better husbandry practices than what we've known in the past," he said. But "we don't feel we're adding a giant population of elderly animals to the zoo. We're just better managing the ones that we do have."
Eventually, difficult decisions have to be made. Animals have adapted to hide their symptoms so predators won't single them out, McClure said. But zookeepers observe their charges closely. They learn to spot subtle changes in behavior and call for medical attention.
Gretchen the giraffe, elderly at 22, had long been treated for arthritis. But in May 2008, she began showing signs of pain. Keepers noticed smaller, slower steps, weaker posture and weight-shifting. They conferred and agreed it was time to euthanize her.
But veterinarians have learned a great deal about how to prolong life at the zoo. Geriatric veterinary care "starts with human medicine," said Ken Ramirez, vice president of Animal Collections and Training at the Shedd Aquarium in Chicago.