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ILAR Journal V37(4) 1995
Fish, Amphibians, and Reptiles
Future Costs of Chimpanzees in U.S. Research Institutions
Bennett Dyke, Sarah Williams-Blangero, Paul M. Mamelka, and William J. Goodwin
| Bennett Dyke, Ph.D., and Sarah Williams-Blangero, Ph.D, are Scientist and Associate Scientist, respectively, and Paul M. Mamelka, B.S., is Senior Systems Analyst in the Department of Genetics, Southwest Foundation for Biomedical Research, San Antonio, Texas. William J. Goodwin, Ph.D., is former Acting Chairman of the Department of Virology and Immunology, and Associate Scientific Director, Southwest Foundation for Biomedical Research, San Antonio, Texas. |
INTRODUCTION
The International Species Inventory System (ISIS) keeps a registry of most of the captive chimpanzees kept in zoos and research colonies throughout the world (Seal and others 1977). The ISIS database recorded a total of 2,572 chimpanzees maintained in captivity worldwide as of January 1995. More than half of these animals (1,455 in all) are housed at 6 biomedical research institutions in the United States. Support for these animals comes principally from commercial sources (mostly the pharmaceutical industry), and National Institutes of Health (NIH) research and animal resource grants and contracts. Chimpanzees have been used extensively in hepatitis vaccine development (Purcell 1992), and are currently the only animal model known to be susceptible to HIV-1 infection (Wiese and Dolatshahi 1994).
In 1973 the United States signed the Convention on International Trade in Endangered Species (CITES), and in 1977 the U.S. Fish and Wildlife Service designated wild chimpanzees as endangered and chimpanzees in captivity as threatened. Since further importation from the wild is prohibited, biomedical research needs for these animals must be met from domestic sources. Because there was concern that fertility, particularly of colony-born animals, might not be high enough to produce enough chimpanzees for U.S. biomedical needs, NIH initiated a chimpanzee breeding and research program in 1986 to help fund production of animals in 5 of the 6 research colonies (Wolfle and April 1994). As the result of developments in husbandry funded in part by these grants, breeding programs in all 6 colonies have been successful, and it appears that the U.S. chimpanzee population as a whole has the capability to be self-sustaining. The biomedical value of chimpanzees lies in their close evolutionary relationship and concomitant physiological and immunologic similarities to humans. These characteristics are balanced against difficulties in caring for such a large, late-maturing, long-lived, behaviorally complex animal, whose husbandry and caging is elaborate and expensive. No doubt the cost of doing research on chimpanzees sets limits on the demand for their use. This, together with the realization that development of effective treatment of AIDS or immunization against the HIV- 1 virus are not at a stage at which the use of chimpanzees might be practicable, has reduced projected demand to the point where many colonies have stopped breeding altogether.
Reducing numbers of births in response to current use carries the risk that insufficient numbers of animals will be produced to replace present cohorts as they age. This could affect the future supply of mature research subjects if and when demand increases. Such a management strategy also reduces numbers of future breeders, jeopardizing production of animals in the future. In the extreme, eliminating births will lead to extinction of the population.
Complicating the problem of managing population numbers is the fact that living animals are seldom removed from these colonies except by sale or trade, and that practically no biomedical experiments involving chimpanzees are immediately terminal. Current practice precludes euthanasia except in cases of deteriorating health, so that in effect, any animal born into the U.S. chimpanzee population can be expected to remain in the population until the time of its natural death. By "natural" we mean simply to exclude any presenescent cause of death recognized as being directly attributable to human intervention.
The aim of this paper is to assess the future financial requirements for supporting the U.S. chimpanzee research population under a variety of assumptions about operating costs and management strategies. We are not concerned with any one colony, but rather with costs incurred by a population aggregate consisting of 6 colonies representing most of the nation's chimpanzees. From this perspective, we ignore accounting practices of individual institutions (that is, distinctions between direct and indirect or overhead costs), since it is the total cost of supporting these animals that we wish to estimate. Likewise we are not concerned here with sources of funding, but rather with estimates of costs that will have to be met no matter what the source. We approach the problem in 2 ways, first to get estimates of per capita costs, and then to make projections of costs for the population aggregate.
FUTURE LIFETIME COSTS OF A SINGLE ANIMAL BORN TODAY
Starting with the assumption that natural death is the only way a living individual can leave the population, lifetime costs are a function only of the mortality schedule that defines age-specific death rates for the population.
Materials and Methods
The standard demographic life table contains a column giving the number of animal-years lived at each age for individuals to which the particular mortality schedule applies. Lifetime cost can be estimated by multiplying each of these values by an anticipated annual maintenance cost and summing the products over the entire life span.
The chimpanzee life table. We have recently published model life tables for both sexes of captive chimpanzees based on aggregated mortality histories of 3 colonies for which detailed mortality statistics were available (Dyke and others 1995). These tables were based on 538 deaths that occurred in a total of 1488 animals at risk. Table 1 gives some characteristics of these schedules. Shown for each sex are proportions surviving through the first year of life, the "expectation of life," or average number of years an individual of a specified age has yet to live, and an estimate of longevity. From the proportions surviving it can be seen that approximately 20% of males and 14% of females die before reaching their first birthday. This early mortality also affects expectation of life which increases once an individual has survived the first 2 or 3 months of high risk.
At the time the model tables were constructed, there were 689 living animals in the 3 colonies, which represents a sample of about 48% of the living population total used in this study.
Maintenance cost estimates. Per diem maintenance costs vary considerably from colony to colony and are notoriously difficult to determine with precision. Our approach to dealing with these uncertainties is to choose a range of plausible values that are likely to encompass rates that actually apply at the colony level. We have chosen 4 per diem values, $15, $20, $25, and $30, which appear to cover total costs of most colonies. This range is intended to allow for differences between such factors as regional operating costs, institutional overhead rates, and colony management aims. The $15 charge is an estimate for colonies whose major focus is maintenance and breeding, while the 3 higher values are typical of costs in colonies that carry out more invasive or hazardous clinical research requiring isolation housing, extensive resident veterinary service, and laboratory facilities.
Results
Our lifetime cost estimates assume that we start with a cohort of animals born in 1995, and that the number of animals against which per diem costs are charged is gradually reduced by mortality as the cohort ages with the passage of time (55 years for males, 60 years for females). In an inflationary economy, the passage of time also increases the costs of maintaining a colony, so in 1 of 2 projections we have incorporated the effects of an annual cost increase of 4%, corresponding approximately to the Biomedical Research and Development Price Index (BRDPI) (Holloway and Reeb 1989). The BRDPI is estimated at 3.9% for 1994, and was projected at 4.0% for 1995 and 4.3% for 1996-2000. We also give a projection using constant 1995 dollars to allow evaluations to be made in terms of current costs. Table 2 shows lifetime costs for a single animal of each sex, based on these assumptions.
Values in all rows of this table increase regularly from left to right simply as a function of per diem costs. The lifetime cost differential between the sexes, however, is greater when inflation is taken into consideration. The projection using 1995 dollars predicts that ultimately a female will cost about 40% more than a male to maintain. This excess increases to about 80% when a 4% inflation rate is used. Costs shown in the table are per capita estimates based solely on the life table, and as such, apply equally well to animals in any colony.
FUTURE POPULATION TOTAL COSTS, STARTING WITH ANIMALS THAT ARE ALIVE TODAY
Estimation of future costs for the population as a whole requires a demographic model that incorporates the current age-sex structure of the population and its reproductive rates, as well as a mortality schedule and financial parameters.
Materials And Methods
Age-sex structure. Numbers of living animals by age and sex were tabulated from the ISIS database as of December 8, 1994 for the 6 U.S. research colonies that contribute vital statistics records to ISIS. These colonies are located at The Coulston Foundation, the Primate Foundation of Arizona, the Southwest Foundation for Biomedical Research (SFBR), the University of Southwestern Louisiana New Iberia Research Center, the University of Texas M.D. Anderson Science Park, and the Yerkes Regional Primate Research Center. Figure 1 shows the age-sex structure, or population pyramid derived from the ISIS database for these 6 colonies combined. Total numbers were 1447 animals (673 males, 774 females). A 7th major U.S. research colony formerly at the Laboratory for Experimental Medicine and Surgery in Primates (LEMSIP) did not contribute to the ISIS database, and so its population numbers are not included here.
The figure consists of 2 histograms arranged base-to-base with bars representing numbers of living males on the left, females on the right. The left vertical axis gives age in 1994 and the right axis gives year of birth. The numbers vary considerably from age to age, which is typical for small populations such as this. The small size of the youngest cohort presumably reflects recent decisions to reduce births; another "pinch" in the structure about 20 years ago resulted from the changeover from importation to colony production of animals effected by the CITES agreement. Mortality accounts for the generally triangular shape of the structure. Here again it can be seen that more females than males live to older ages, a feature that is more frequently seen in human populations than in the various monkey populations we have analyzed (Gage and Dyke 1988; Dyke and others 1993).
Reproductive rates. For this study we used age-specific fertility rates (ASFR) based on records from the SFBR colony, which contain detailed information about breeding performance. The ASFR schedule consists of average numbers of live births occurring to living females at each age, and measures reproduction without regard to actual breeding status (that is, whether or not an animal is on a contraceptive regimen or caged in a stable social group with 1 or more compatible males).
Population fertility is conveniently summarized by the Total Fertility Rate (TFR), which is the sum of the ASFR over all maternal ages, and which represents an estimate of the number of births that the average female potentially might have if she survived and remained a breeder from beginning to end of the reproductive ages. Females of known fertility in this colony gave birth between the ages of 7 and 39 (mode 22.5 years) and had an average of 3.86 offspring. The TFR calculated from the fertility schedule is 8.12, suggesting that females could have produced many more offspring than they actually did, had they been allowed to breed without restriction. The sex ratio at birth is approximately equal.
Mortality schedules and financial parameters. Mortality schedules used are the same as those chosen for estimation of lifetime maintenance costs described above. We again show results for both constant 1995 dollars and a 4% inflation rate, but limit calculations to the single case of $25 per diem, which we take to be a plausible mid-range value for the majority of U.S. research colonies.
Projection model. The projection model, QuickSim, is part of an animal colony demographic analysis software package written at SFBR for the Apple Macintosh computer (Dyke and Mamelka 1989). The program is based on a conventional deterministic Leslie Matrix algorithm, but incorporates a financial component, as well as capabilities for modeling harvest, culling, and utilization.
Two scenarios were chosen for analysis because they represent plausible alternative approaches to managing the U.S. chimpanzee population in the face of increasing pressures on biomedical research funding. The apparent limited research demand for chimpanzees eliminates population growth as a goal, necessitating fertility control to restrict population growth. One of the strategies evaluated is simply to stop breeding altogether and allow the population to gradually die out (the "no births" scenario). The other is to maintain the population at its present size by adjusting fertility rates to match death rates (the "no growth" scenario). In both cases simulations were run for a total of 60 years, the maximum survival of individuals born in the initial year. Only a small minority of animals is expected to survive to this advanced age, a fact that is taken into account in the age specific probabilities of dying that make up the mortality schedule (Dyke and others 1995).
Results
No births scenario. Table 3 gives total population cost estimates for the no births scenario based on a $25 per diem charge projected for both 1995 dollars and a 4% inflation rate. Annual and cumulative costs are given at single intervals for years 1-5 (covering the duration of a typical NIH grant), at intermediate years 10 and 20, and at the end of each 60-year projection. Population sizes are the number of animals living at year end, while costs are computed on the basis of the mid-year population.
It can be seen that with inflation, values in the Annual Expenses column increase through year 20, despite a decline in population size. This is shown in more detail in the upper curve of Figure 2, which plots annual costs by each year of the entire 60-year duration. A maximum of $15,374,543 is reached in the 18th year, after which costs level off briefly, and then begin a rapid decline.
No growth scenario. Table 4 repeats the entries of Table 3 for the No Growth scenario. Here population size remains fixed at 1447 animals. The noninflated annual expenses also remain constant, while the inflated annual expenses increase over the entire period.
Discussion
It is important to recognize limitations of the modeling approach, and to understand sources of uncertainty in interpreting results:
1. Errors in measurement or specification of parameters may accumulate as they are propagated through simulated time. Basing parameter estimates on data of high quality (which is available for chimpanzees) can reduce this problem. For planning purposes it is also important to re-run projections regularly (perhaps annually), updating parameter estimates when appropriate, and re-evaluating the results.
2. There is no assurance that parameter estimates based on past measurements will apply in the future. Some parameter estimates may be more vulnerable to uncertainty than others. For example, economic factors such as inflation rates and per diem costs may fluctuate more than demographic rates. One means of circumventing this limitation is by choosing a range of input values so that results are likely to encompass some reasonable true value (as we have done here with per diem charges).
3. Particular scenarios may be more sensitive to sources of error than others. For example, mortality and financial estimates are critical in this study, whereas the level of fertility required for the no growth scenario is so low that the actual fertility schedule used is unimportant so long as number of births keep up with deaths (the SFBR fertility schedule used without "birth control" causes the population to increase by a factor of 12 by the end of the 60-year duration of the simulation).
4. Modeling itself is a process of abstraction and simplification, which may introduce errors even if critical components of the real-life system have been identified and mimicked explicitly in the model. For example, we have achieved the no growth scenario in the simulation by specifying that numbers of births exactly equal numbers of deaths. In reality, precise control of fertility is unlikely, and population numbers would fluctuate as a result. Likewise, by using a deterministic model we fail to take into account stochastic variability in both birth and death rates that would also affect population growth and age structure. By deliberately ignoring complexity in the modeling process, however, we clarify the consequences of varying individual parameters, and we develop easily interpretable benchmarks against which to compare real-life measurements.
As a consequence of these cautions, we have not attempted to make precise predictions of future values for long-term budgetary planning, a task that is beyond the capability of any simulation model, which simply carries out its underlying assumptions to their logical conclusions. Rather, our strategy has been to compare effects of varying selected assumptions, and to define a scale of expenditure that can be anticipated if particular conditions were to hold.
This approach yields a number of important conclusions.
1. The birth of a chimpanzee into any U.S. colony initiates a substantial long-term obligation of funds.
2. When inflation of magnitudes associated with the BRDPI is taken into account, apparent costs are likely to continue rising even if the decision is made to allow the population to die out as the result of natural death. This is because initial decreases in population size due to mortality may not be sufficient to overcome effects of inflationary increase.
3. Differences between the 2 management scenarios analyzed initially appear minimal, amounting to about a 6% excess in cumulative cost (1995 dollars) of no growth compared to the no birth policy at the end of the first 5 years, by year 20, however, this excess will have grown to 30%, and by year 60 replacement costs will have exceeded costs of the no births policy by a factor of 2.6 in 1995 dollars (or 5.1 with 4% inflation).
4. The lifetime cost of maintaining females is greater than that for males, because females live longer than males. The male-female cost differential is increased when inflation is taken into account. These results ignore the possibility that per diem charges may differ between the sexes.
Dollar amounts required to maintain national chimpanzee research resources are likely to be sizeable, whether the population is maintained as a viable productive entity or allowed to die out. Other less costly strategies than those modeled here should be explored. These might include:
1. A change in practice that would permit euthanasia of some older animals, particularly those that exhibit severe medical or behavioral pathologies that preclude more cost-effective social housing.
2. Gradual reduction of the current population (possibly using a no birth policy) to some minimum survival size on the basis of conservation guidelines such as those recommended in Species Survival Plans developed by the American Zoo and Aquarium Association (Wiese and Hutchins 1994).
3. Formation of one or more retirement facilities to which animals from existing colonies could be transferred. Several groups have explored the possibility of establishing a retirement facility for chimpanzees no longer needed in biomedical research. It is anticipated that group housing and reduced handling of animals would reduce operating costs below those typical of research facilities. Presumably, projections based on a $15 per diem charge would be closer to the future costs of a sanctuary than are those shown in Tables 3 and 4 (the $15 rate reduces all values in these tables by 40%).
Chimp Haven, an unaffiliated nonprofit organization in Texas, has formulated a preliminary fund-raising plan using detailed long-term actuarial projections based on the methods described in this paper. Given a range of projected inflation and interest rates, it appears that an endowment sufficient to maintain the proposed population over the long-term is a feasible goal.
Careful scientific, financial, and ethical consideration will be required for the long-term management of these animals. The modeling methods used here should play an integral part in these considerations, as well as in management planning at the individual colony level (Williams-Blangero and others 1994).
ACKNOWLEDGEMENTS
Supported by NIH Grants RRO2229 and RRO9950 (to B. Dyke) and RRO8122 (to S.W. Blangero). Summary statistics of chimpanzee population structure were provided by the International Species Inventory System, Minnesota Zoological Garden, Apple Valley, Minnesota. Comments by N. Flesness and D.R. Lukens of ISIS, J. Fritz of the Primate Foundation of Arizona, L. Whitehair of the National Institutes of Health, T. Butler and J.L. VandeBerg of the Southwest Foundation, and two anonymous reviewers are gratefully acknowledged.
REFERENCES
Dyke B, Mamelka PM. 1989. ACMP, an Animal Colony Management Package User's Guide. Population Genetics Laboratory Technical Report No. 3. San Antonio, TX: Southwest Foundation for Biomedical Research.
Dyke B, Gage Tn, Ballou JD, Petto AJ, Tardif SD, Williams LE. 1993. Model life tables for the smaller New World monkeys. Am J Primatol 29:269-285.
Dyke B, Gage Tn, Alford PL, Swenson B, Williams-Blangero S. 1995. A model life table for captive chimpanzees (Pan troglodytes). Am J Primatol 37:25-37.
Gage Tn, Dyke B. 1988. Model life tables for the larger Old World monkeys. Am J Primatol 16:305-320.
Holloway TM, Reeb JS. 1989. A price index for biomedical research and development. Public Health Rep 104:11-13.
Purcell RH. 1992. Primates and hepatitis research. In: Erwin J, editor. Chimpanzee Conservation and Public Health: Environments for the Future. Rockville, MD: Diagnon/Bioqual. p 15-20.
Seal US, Makey DG, Bridgewater D, Sinunons L, Murtfeldt LE. 1977. ISIS: A computerized record system for the management of wild animals in captivity, lnt Zoo Yearb 7:68-70.
Warren JT, Dolatshahi M. 1994. Annual updated survey of worldwide HIV, SIV and SHIV challenge studies in vaccinated nonhuman primates. J Med Primatol 23:184-225.
Wiese RJ, Hutchins M. 1994. Species Survival Plans: Strategies for Wildlife Conservation. Wheeling, WV: American Zoo and Aquarium Association.
Williams-Blangero S, Goodwin WJ, Dyke B. 1994. Structuring demographic and genetic management programs for the long-term maintenance of a chimpanzee colony. Abstracts of the 15th Congress of the International Primatological Society 15:158.
Wolfle TL, April M. 1994. The US chimpanzee breeding and research program. In: Eder G, Kaiser E, King FA, editors. The Rule of the Chimpanzee in Research. Basel, Switzerland: Karger. p 79-86.
TABLE 1 Some characteristics of captive chimpanzee model life tables (Dyke and others 1995)
| Porportion surviving to age 1 | Expectation of life at birth | Maximum expectation of life | Maximum age | |
| Males | 0.8077 | 20.8 | 25.0 at 2 mo. | 55 |
| Females | 0.8597 | 29.4 | 33.5 at 3 mo. | 60 |
TABLE 2 Estimated individual lifetime costs for both sexes based on chimpanzee model life tables at four different per diem rates
| $15 | $20 | $25 | $30 | |
| Males | $113,430 | $151,240 | $189,050 | $226,860 |
| Females | $160,860 | $214,480 | $268,090 | $321,710 |
| $15 | $20 | $25 | $30 | |
| Males | $242,130 | $322,840 | $403,560 | $484,270 |
| Females | $443,950 | $591,930 | $739,910 | $887,890 |
TABLE 3 Estimated future population total costs, $25 per diem. No births scenario.
| Year | Date | Size | Annual Expenses | Cumulative Balance | Annual Expenses | Cumulative Balance |
| 0 | 1447.0 | $0 | $0 | $0 | $0 | |
| 1 | 1995 | 1408.2 | 13,026,980 | 13,026,980 | 13,026,980 | 13,026,980 |
| 2 | 1996 | 1375.3 | 12,699,900 | 25,726,880 | 13,207,900 | 26,234,880 |
| 3 | 1997 | 1342.6 | 12,400,360 | 38,127,240 | 13,412,230 | 39,647,110 |
| 4 | 1998 | 1309.9 | 12,102,270 | 50,229,510 | 13,613,400 | 53,260,510 |
| 5 | 1999 | 1277.4 | 11,805,170 | 62,034,680 | 13,810,380 | 67,070,900 |
| 10 | 2004 | 1114.5 | 10,319,020 | 116,600,540 | 14,687,180 | 138,832,920 |
| 20 | 2014 | 781.2 | 7,281,370 | 203,147,100 | 15,340,740 | 290,896,250 |
| 60 | 2054 | 0.0 | 2,980 | 299,865,210 | 30,120 | 611,641,740 |
TABLE 4 Estimated future population total costs, $25 per diem. No growth scenario.
| Year | Date | Size | Annual Expenses | Cumulative Balance | Annual Expenses | Cumulative Balance |
| 0 | 1447.0 | $0 | $0 | $0 | $0 | |
| 1 | 1995 | 1447.0 | 13,023,880 | 13,023,880 | 13,203,880 | 13,203,880 |
| 2 | 1996 | 1447.0 | 13,023,880 | 26,407,750 | 13,732,020 | 26,935,900 |
| 3 | 1997 | 1447.0 | 13,023,880 | 39,611,630 | 14,281,310 | 41,217,210 |
| 4 | 1998 | 1447.0 | 13,023,880 | 52,815,500 | 14,852,560 | 56,069,770 |
| 5 | 1999 | 1447.0 | 13,023,880 | 66,019,380 | 15,446,670 | 71,516,440 |
| 10 | 2004 | 1447.0 | 13,023,880 | 132,038,730 | 18,793,240 | 158,527,140 |
| 20 | 2014 | 1447.0 | 13,023,880 | 264,077,500 | 27,818,550 | 393,185,980 |
| 60 | 2054 | 1447.0 | 13,023,880 | 792,232,500 | 133,557,460 | 3,142,397,290 |
FIGURE 1 Age-sex structure of 6 U.S. chimpanzee colonies combined.
FIGURE 2 Estimated future annual expenses by year, $25 per diem. No births scenario.
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