Why Do Most Captive Great Apes Have Heart Disease?

captive great apes

Story at-a-glance -

  • About 70 percent of captive adult male gorillas in North America suffer from heart disease; it’s the leading cause of death among this population, but in wild gorillas, heart disease is virtually nonexistent
  • In addition to gorillas, other great apes, including orangutans, chimpanzees and bonobos also suffer from high rates of heart disease in captivity
  • Changes in gut bacteria have been noted in humans with heart disease, and suggests this may be the case in gorillas as well
  • After analyzing feces from eight captive gorillas to determine the types of bacteria in their guts, they found significant differences in the bacterial composition between gorillas with and without heart disease
  • It’s also been shown that captivity and loss of dietary fiber led to a loss of native gut microbiota and “humanization” of the microbiome in nonhuman primates

By Dr. Karen Shaw Becker

About 70 percent of captive adult male gorillas in North America suffer from heart disease. It’s the leading cause of death among this population,1 but in wild gorillas, heart disease is virtually nonexistent. In addition to gorillas, other great apes, including orangutans, chimpanzees and bonobos also suffer from high rates of heart disease in captivity. The problem has been known for decades, but little has been known about ape hearts to establish an effective plan for treatment and prevention.

In fact, when the first gorilla was brought to the Bronx Zoo in New York in 1911, she was fed meat but, being primarily an herbivore, she refused it and died as a result within just two weeks. Later gorilla diets were not much better, consisting sometimes of milk, yogurt, eggs, meat, bread and popcorn.

“The invention of processed, calorically dense ‘biscuits’ packed with vitamins and nutrients and supplemented with a few fruits and vegetables eventually helped standardize gorilla diets,” The Atlantic reported,2 as well as lengthened lifespan in captive gorillas. But, much like standardized kibbles for cats and dogs, the biscuits still leave much to be desired compared to a wild gorilla’s diet, which consists of stems, bamboo shoots, fruits and the occasional termite nest.

It’s becoming clear that diet may play a role in the rise in heart disease in captive gorillas, particularly due to its influence on the gut. Mary Ann Raghanti with Kent State University, who studies great ape heart health, told The Atlantic, “I started studying the brain because I thought it was in control, but really it’s the gut. The gut dictates everything.”3

Is Gut Health Behind Rising Rates of Heart Disease in Captive Great Apes?

Uncovering what could be behind heart disease in apes has been a challenge, in large part because it can be dangerous to put apes with heart disease under anesthetic. For years, study into captive apes’ heart disease faltered for this reason, until apes began to be trained to hold still for voluntary heart check-ups, including blood pressure readings, blood tests and cardiac ultrasounds. This makes it possible for heart disease to be diagnosed and treatments, including prescribed human heart medications, started.

With increasing data about the prevalence and types of heart disease in captive gorillas increasing, some experts began to wonder whether diet could be playing a role, as it does in human heart disease. While the gorilla biscuits give the animals the basics they need to survive, they’re not really species-appropriate for great apes, which are hind-gut digesters, similar to horses, making them excellent at breaking down fiber.

In the wild, gorillas may spend the majority of their day foraging for food, which may be why some captive gorillas often regurgitate their food in order to eat it again — it extends the amount of time they spend eating and looking for food.

At the Cleveland Zoo, keepers introduced a new, more natural diet, the so-called Cleveland diet, consisting of leafy greens, alfalfa and tree branches, which increased the gorillas’ fiber intake and time spent eating. Regurgitation and re-ingesting stopped almost immediately, while decreases in fat, cholesterol and gut bacteria were also noted.4

Changes in gut bacteria have been noted in humans with heart disease, and research by Katherine Krynak, Ph.D., an assistant professor of biology at Ohio Northern University, and colleagues suggests this may be the case in gorillas as well. After analyzing feces from eight captive gorillas to determine the types of bacteria in their guts, they found significant differences in the bacterial composition between gorillas with and without heart disease. Specifically, they noted:5

“Bacterial operational taxonomic units from phyla Bacteroidetes, Spirochaetes, Proteobacteria and Firmicutes were significant indicators of cardiac disease. Our results suggest that further investigations between diet and cardiac disease could improve the management and health of zoo-housed populations of this endangered species.”

Captivity ‘Humanizes’ Primates’ Microbiome

While longer lifespans that tend to occur in captivity have been suggested as one reason why captive apes get heart disease more often than their wild ape counterparts, the gut theory is gaining a foothold. What’s more, it’s already been shown that living in captivity leads to notable changes in nonhuman primates’ microbiome. The microbiome refers to the trillions of bacteria living in the primate gut.

Changes in these bacteria are associated with a variety of metabolic and autoimmune diseases in humans, so it stands to reason that this could occur in apes as well. One study on nonhuman primates even revealed that captivity and loss of dietary fiber led to a loss of native gut microbiota and colonization with bacteria common in the modern human gut microbiome instead.

“These results demonstrate that captivity and lifestyle disruption cause primates to lose native microbiota and converge along an axis toward the modern human microbiome,” the study concluded.6

At the Cleveland Metroparks Zoo, gorilla keepers are trying to combat this by adding resistant starch into the gorillas’ diet in order to mimic the fiber a gorilla would consume in the wild, along with leafy greens scattered throughout their enclosure to allow for “foraging.”7 Further, the more species-appropriate Cleveland diet has been introduced at four zoos throughout North America.

It’s too soon to tell whether these changes will lead to improvements in apes’ heart health, but if what’s occurred in dogs is any indication, the answer is likely to be yes. Optimizing gut microbiota in dogs, as well as humans, is known to help prevent and treat a variety of diseases, so doing so in apes will likely lead to favorable health outcomes as well.