On any given day, the Dallas Zoo’s three veterinarians might work on a tiny frog who weighs a few grams and then examine an elephant that weighs 10,000 pounds. That’s the irony of “specializing” in zoo veterinary medicine: one must be a generalist for hundreds of mammal, bird, reptile, fish, and invertebrate species.

Vets must know how to recognize different digestive, vascular, and reproductive systems; infectious and chronic illnesses; pharmacological needs; and animal behaviors in order to develop courses of care.

MEDICATIONS: Administering drugs isn’t simple as picking up a ‘script from Walgreen’s. Zoo vets often have to improvise when calculating drug dosages, because pharmaceutical companies don’t publish formulations for every species. The vets know that a published dosage for a horse would be good for a zebra, or that antibiotics effective on lizards would probably work with snakes. Compounding pharmacies may be used to create concentrated volumes for large-animal needs.

“But you can’t just increase the dosage of some drugs because the animal is bigger,” explained Christopher J. Bonar, V.M.D., Dipl. A.C.Z.M., director of animal health. “Sometimes we have to do metabolic scaling to formulate dosages based on an animal’s metabolic rate. Large animals like rhinos have a slow metabolism.”

SPECIALTY EQUIPMENT: When necessary, veterinarians must be creative with equipment to accommodate everything from tiny poison dart frogs to long-necked giraffes. They’ve turned urinary catheters into endotracheal tubes. Anesthesia masks have been made from pop bottles and construction cones.

Dr. Maren Connolly examines koala Tekin while he’s under anesthesia as part of his annual checkup. Dallas Zoo/Cathy Burkey

ANESTHESIA: Like with humans, putting an animal “under” and performing surgery are last resorts. That’s why zookeepers train animals to demonstrate behaviors that make it easier to draw blood, administer shots, and conduct exams.

There are a few times when anesthetizing an animal is risky – for the vets! Herpetologists noticed that a red spitting cobra wasn’t eating or defecating, and had a swollen abdomen. The snake had a history of kidney problems, common to this species. The challenge was to sedate the venomous snake.

“Our very skilled snake keepers helped on this one,” Bonar said. The dangerous end of the cobra was drawn into a plastic tube so the vets could pump gas to anesthetize it. “We inserted a tube into the trachea to ventilate it during surgery and confirmed that the snake had a renal tubular carcinoma. After testing the other kidney to make sure it was functioning well, we removed the affected kidney.”

BIRTH DAYS: It’s exciting when babies are born – or hatched. Newborn antelopes and other herd animals are often checked and tagged 48 hours after birth. Although recognizing newborns may seem simple, herd animals often deliver at the same time of year, and the babies look strikingly similar. Vets check the mother’s lactation and the baby’s suckle response and hydration. During difficult labors, vets may manually assist with breech births or perform C-sections.

Keepers trained Ramona chimp to allow an ultrasound during her pregnancy to check on the fetus. Dallas Zoo/Cathy Burkey

Vets monitor hormone levels or perform ultrasounds for some expectant mothers, such as Marge warthog and Ramona chimpanzee. Both mothers were trained to allow vets or a veterinary ultrasonographer to apply a jelly-like substance to their bellies for the test to check the fetus’s health and estimate due dates. Ramona even learned to hold on to the bars of her bedroom to make the job a little easier. After babies are born, vets usually wait to do well-baby exams until mom is ready to eat away from the baby or share care with others in the group.

Zoo populations often use the same methods as humans to limit or facilitate pregnancies. Many animals are on birth control so the population doesn’t get out of control or inbreeding doesn’t occur. In cases where there is a need to increase the population or genetic diversity of a species in the Association of Zoos & Aquariums (AZA) Species Survival Program (SSP), vets may use assisted reproduction.

“We always prefer natural reproduction,” Bonar said. “Techniques that work with a horse or cow won’t necessarily work with a rhino or cheetah. We work with the SSPs and a company that does hormone analysis and makes reproductive recommendations for us. But basically we watch to see if the females are coming into estrus. Are the males fertile? Are the animals compatible? Sometimes absence makes the heart grow fonder, and we recommend a simple change in environment for a short time.”

Zoos with expertise in breeding certain species often serve as consultants. The Dallas Zoo advises on okapi breeding at other facilities.

Advanced Diagnostics: Bonar and his team of vets routinely test blood or tissue samples, but they often send them to more than a dozen pathology labs, each one specializing in a certain species or test. When an animal passes away; vets perform necropsies to determine the cause of death so that information can contribute to the body of knowledge among scientists and zoo professionals. When possible, tissue and bones are donated for educational purposes.

In the wild, many animals don’t exhibit obvious signs of illness because other members of its group may perceive it as weakness or because the animal may become easy prey. Diagnosing challenging cases may require the services of offsite computed-tomography (CT) or magnetic-resonance imaging (MRI) facilities.

Outside medical specialists allow the hospital team to extend their resources. The Dallas Zoo routinely works with specialists on cases requiring ophthalmic or dental surgery, CT or MRI scans, pathology results, and hoof trims. That’s why the Zoo is assembling a Medical Advisory Committee. The depth of knowledge of the Zoo’s veterinary team, combined with the expertise of several specialists, will help provide even better care.