The paradoxical increase in the use of primates in research

Over the last two decades, we have seen a somewhat steady decline in research-oriented use of all classes of animals covered by the Animal Welfare Act—but for one stubborn and puzzling exception. That exception has to do with non-human primates, paradoxically among the more popular animals. The following graph shows this trend by plotting the percentage change since 1973 in the number of animals used in research for each class of animals reported by the USDA (for farm animals, I use 1991 as the reference since that is the year in which the USDA began fully reporting their numbers.)

Percentage change in the number of animals used in research compared to the number used in 1973 (or 1991 for farm animals)

The graph above makes clear that something very different is going on in the matter of non-human primates used for research. It is an outlier of some sort—there is apparently something atypical about the combination of social, economic, political and scientific forces that determine how many primates get used in research. One distinction, of course, is that non-human primates are our closest relatives in the animal kingdom and the public empathizes with them more than they do with farm animals, guinea pigs or hamsters. So, it is paradoxical that our use of non-human primates has actually been increasing—especially sharply during the last decade—at the same time as the number of animals of other classes used in research has been declining. What can explain this paradox? I have two hypotheses to offer, but insufficient evidence to ascertain the validity of either of them.

Sources cited
  1. USDA. A Review of the Animal Welfare Enforcement Report Data: 1973 Through 1995. Animal Welfare Information Center Newsletter 7(2), 1996. (link, accessed January 1, 2013)
  2. USDA, Animal and Plant Health Inspection Service. Animal Care Annual Report of Activities: Fiscal Year 2007. February 2011. (link, accessed January 1, 2013)
  3. USDA, Animal and Plant Health Inspection Service. Annual Report: Animal Usage by Fiscal Year (2008). February 2011. (link, accessed January 1, 2013)
  4. USDA, Animal and Plant Health Inspection Service. Annual Report: Animal Usage by Fiscal Year (2009). February 2011. (link, accessed January 1, 2013)
  5. USDA, Animal and Plant Health Inspection Service. Annual Report: Animal Usage by Fiscal Year (2010). July 2011. (link, accessed January 1, 2013)
  6. Department of Defense. Animal Care and Use Reports for Fiscal Years 1994 to 2007 (11 reports). (link, accessed January 9, 2012)

Hypothesis 1: People and institutions find ways to skirt regulations they find inconvenient. Scientists and research institutions are no exception. One easy way to avoid the accountability imposed by the Animal Welfare Act is to conduct research on animals not covered by the Act, such as rats and mice. Maybe, many scientists over the last two decades have replaced guinea pigs, rabbits, hamsters, and others with rats and mice in their research to avoid the welfare requirements of the Act. Maybe, primates are not so readily replaced by rats and mice in most experiments and, so, their numbers in research have kept on increasing while the numbers of other animals covered by the Act have declined.

If this hypothesis is correct, then the percentage of animals used in research that are not covered by the Animal Welfare Act should have increased substantially during the last couple of decades. But, nobody really knows how many of these animals (rats, mice, and most non-mammals such as birds) are in use in research since there are no federal reporting requirements on them. However, the Department of Defense, probably among the largest users of animals for research, reports numbers of all animals it uses. According to its reports on animal care and use, the percentage of animals used in their research but not covered by the Animal Welfare Act has actually gone down from a high of 95.4% in 1994 to a low of 90.26% in 2007 (the latest year for which the data have been made available), as shown in the graph below.

Percentage of rats, mice, and non-mammals (animals not covered by the Animal Welfare Act) among animals used for research by the Department of Defense

This data from the Department of Defense offers information on only a sample of all animals used for research in the US, but it does cast some doubt on the validity of Hypothesis 1. We will not have any better evidence for or against this hypothesis unless new laws require the USDA to include all animals in their administration of the Animal Welfare Act. Until then, I am inclined to believe that Hypothesis 1 is more likely false than true.

Hypothesis 2: Maybe, animal advocates are having an impact and have been successful in pressuring scientists, grant reviewers, and government agencies to put a little more thought into the need and the scientific validity of their experiments on animals. Since the most compelling justification of need is usually based on what will advance human health and since non-human primates are our closest relatives, an experiment involving non-human primates is more readily perceived as having scientific validity and relevance to human health (even if this may not always be true). An experimenter, therefore, may feel a tug toward choosing non-human primates over other classes of animals in his/her research to increase the perceived validity of the research, especially when this choice does not involve any new reporting requirements or additional welfare regulations. If Hypothesis 2 is true, animal advocates should feel encouraged because it suggests that they have been able to cause enough of a systemic shift to change how research on animals is perceived by the very people engaged in it.

So, which hypothesis are you inclined to believe? Could it be that the paradoxical increase in the number of non-human primates used in research is actually an unintended consequence of the success of animal advocates? Do you have another hypothesis that better explains the paradox?


Silly Man

Even if Hypothesis 2 did increase the number of primates in use (which is sad), it is nice to see that AR activists are capable of having an impact on how such research is conducted. Hopefully, the total number of all animals used is reducing overall.


The USDA really needs to include all animals in the Animal Welfare Act. I am sure most people believe that it already does.


Spike, yes, all animals should be counted. Here is a compelling PETA video making the case for rats and mice.


Hypothesis 3: Experimentation on NHPs is increasingly banned in other countries (uk,nz,austria,sweden,neth etc) so while the worldwide # of primates used may be steady or even declining, the portion used in the us is increasing.


Thank you, Anonymous, for Hypothesis 3! This gives me an idea for a future post comparing the trends in the US with those in other countries that also have some reporting requirements on animals used in research.


hypothesis 1 holds a lot of truth. DoD numbers likely don't reflect the exponential growth in use of transgenic rodents. Some estimates put the number of mice used over 100 million a year. I'm not sure the move to mice is driven by a desire to avoid the AWA. I think it's more that the research industry has successfully blocked AWA coverage of their preferred species.

Primate use has increased at least in part due to a steady supply bred in the National Primate Research Centers, and imported from South Asian countries. It used to be much harder to get monkeys.

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