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Rhesus macaques are among the most popular nonhuman primates used in biomedical research.

AP Photo/Brennan Linsley

Record number of monkeys being used in U.S. research

*Update, 14 April 2020, 10:45 a.m.: Since this article was published, the United States Department of Agriculture has twice modified the number of monkeys used in U.S. research in 2017. The latest figure from the agency is 74,498 monkeys used in 2017, which confirms that 2017 was a record year for monkey use.

Here is our original story from 2 November 2018: 

The number of monkeys used in U.S. biomedical research reached an all-time high last year, according to data released in late September by the U.S. Department of Agriculture (USDA).

The uptick (see graph below)—to nearly 76,000 nonhuman primates in 2017—appears to reflect growing demand from scientists who believe nonhuman primates are more useful than other animals, such as mice or dogs, for testing drugs and studying diseases that also strike humans.

“I think the numbers are trending up because these animals give us better data. … We need them more than ever,” says Jay Rappaport, director of the Tulane National Primate Research Center in Covington, Louisiana, which houses about 5000 monkeys. The increase also comes amidst a surge in funding from the National Institutes of Health (NIH), which supports much of the nonhuman primate research in the United States.

The figures have surprised and disappointed groups seeking to reduce the use of lab animals. The biomedical community has said it is committed to reducing the use of research animals by finding replacements and using these animals more selectively, says Thomas Hartung, director of Johns Hopkins University’s Center for Alternatives to Animal Testing in Baltimore, Maryland. But the new numbers suggest “people are just blindly running toward the monkey model without critically evaluating how valuable it really is.”

Nonhuman primate research has faced intensifying scrutiny. Harvard University closed its national primate research center—one of only eight in the country—in 2015, after a federal investigation into the deaths of four of its animals. That same year, NIH ended its support of all invasive chimpanzee studies, citing a report that found these animals were no longer essential to biomedical research. And in 2016, Congress directed NIH to hold a workshop on the utility and ethics of monkey research.

Monkeys on the rise

Trends in the use of various research animals as a percentage change over their 2008 numbers

-40 -30 -20 -10 0 10 20 Monkeys Cats Dogs Guinea pigs Rabbits 2008 Percent 2009 2010 2011 2012 2013 2014 2015 2016 2017

Public opposition to animal research has been rising—with a recent Pew Research Center poll finding that a record 52% of Americans oppose such studies. And importing monkeys to the United States has become increasingly difficult as almost all commercial air carriers now refuse to fly the animals.

Yet according to the new USDA figures, scientists used 75,825 nonhuman primates for research last year, up 22% since 2015 and 6% since 2008. In contrast, the number of cats, dogs, rabbits, and other animals recorded by USDA are all being used at lower numbers than they were a decade ago. (Nonhuman primates constitute just 0.5% of all animals used in U.S. biomedical research; about 95% are rats and mice, which are not reported by USDA.) The total number of monkeys in labs—which also includes those bred in colonies and those not currently being used in research—has remained fairly steady for the past decade, with about 110,000 recorded last year (see second graph, below).

The uptick in monkey research “represents both the state of the science and the importance of nonhuman primates,” NIH said in a statement. Nearly two-thirds of the nonhuman primates the agency supports are rhesus macaques, with cynomolgus macaques (15%), baboons (6%), and a dozen other monkey species making up the remainder. The rising demand for rhesus macaques appears to be driven by researchers studying HIV/AIDS, the brain, Alzheimer’s disease, and addiction, according to an NIH report released in September. 

The rise might also reflect the agency’s expanding investment in these studies. NIH gave 249 grants in 2017 that supported nonhuman primate research, up from 171 in 2013. And the agency expects the number of nonhuman primates it supports to continue to grow in coming years.

Growing demand

The total number of monkeys in research labs has not changed much in the past few years, but more are being used in studies.

Number of nonhuman primates 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 0 50,000 100,000 150,000 Bred and housed Experimented

That forecast frustrates Hartung, who says NIH should launch a review of the need for monkeys, similar to the one that led it to end its support for chimpanzee research. He challenges the idea, for instance, that nonhuman primates are more useful for drug testing than rats or mice. Nonhuman primates are more genetically variable than rodents, he argues, and researchers typically use relatively few monkeys for studies of drug efficacy and safety. As a result, those experiments could yield skewed data on how the drugs will act in humans. Scientists embracing monkey experiments, he says, are at risk of “repeating the mistakes of the past.”

Other animal advocates hope the new statistics will move members of Congress to put greater pressure on U.S. agencies to reduce nonhuman primate use. “I think when Congress sees these numbers, things are going to come to a head,” says Mike Ryan, director of policy and government affairs at the New England Anti-Vivisection Society in Boston. This week, Representative Brendan Boyle (D–PA)—reacting to an investigation into the Food and Drug Administration (FDA) by the Washington, D.C.–based animal activist White Coat Waste Project—sent a bipartisan letter to FDA asking it to review all studies involving the more than 300 nonhuman primates it oversees. “Painful primate testing is shameful, and it has no place in the 21st century,” Boyle tells Science. “It’s clear that federal agencies are still not doing enough to curb this appalling practice.”

In the meantime, Rappaport says nonhuman primate facilities like his are simply struggling to meet the demand. Some scientists are reporting that they have delayed studies by at least 6 months because they can’t obtain animals, the NIH report notes. The growing demand could sharpen the tensions surrounding animal research. “The public wants more cures, but fewer animals,” says Cindy Buckmaster, board chair of the Washington, D.C.–based Americans for Medical Progress, which supports animal studies. “They can’t have it both ways.”