Improving transparency-A call to include social housing information in biomedical research articles involving nonhuman primates.

The social setting of animal subjects in the research environment has known effects on a variety of dependent measures used in biomedical research. Proper evaluation of the robustness of published research is dependent upon transparent, detailed, and accurate reporting of research methods, including the animals' social housing conditions. However, to date, most research articles utilizing nonhuman primates (NHPs) provide only partial data on this topic, hampering transparency, and reproducibility. Therefore, we call for the inclusion of information pertaining to the social aspects of the animals' housing conditions in publications involving NHPs to improve transparency. We argue that including this information in scientific publications is crucial for the interpretation of research findings in the appropriate context and for understanding unexplained variability in study findings. Finally, the inclusion of this information in publications will additionally familiarize scientists with how other researchers conducting similar studies are housing their animals and will encourage them to consider the implications of various housing conditions on their research outcomes.

Weight management towards physiological and behavioral wellbeing for chimpanzees living under human care.

Across a period of 54 months, several changes were made to the feeding protocols of 32 adult chimpanzees living at the Yerkes National Primate Research Center Field Station. Before implementing any changes in diet, baseline data were collected for 6 months. During Baseline (BS), the chimpanzees received unlimited amounts of primate biscuits twice a day and a limited amount of produce as enrichment. Treatment One (T1) dietary modifications included an increased amount of vegetables, primarily leafy greens, and biscuit feedings scheduled to occur an hour after vegetables were provided to the chimpanzees. T1 lasted for 1 year. At the end of T1, most of the chimpanzees had gained weight. Treatment Two (T2) occurred over the span of 3 years, during which all the chimpanzees were switched from unlimited, group-distributed primate biscuits to individually prescribed amounts of biscuits, fed in\dividually, and increased daily feedings of leafy greens. By the end of T2, 10 of 15 chimpanzees who were overweight or obese at the start of the project were within range of ideal body condition, and 4 of the remaining 5 were improved. All the chimpanzees who started the project within ideal range were still within ideal range. Significantly more time was invested in eating, foraging, and processing food during T2 (p < .05), more appropriately replicating the natural time budget for a chimpanzee. There were not any increases in abnormal, stress-related, or agonistic behaviors as a function of dietary modifications. Inactivity, however, was significantly higher (p < .05) during the later protocol, and locomotion was concurrently lower (p < .05).

Effects of medroxyprogesterone acetate on social behavior in female rhesus macaques (Macaca mulatta) depend on male breeding season introductions.

BACKGROUND: Although medroxyprogesterone acetate (MPA) is used commonly as a contraceptive in women and female non-human primates, its effects on social behavior remain unclear. This study examined whether MPA treatment and introduction of new adult males during the breeding season influence the social behaviors of group-housed adult female rhesus macaques. METHODS: Subjects were 12 MPA-treated and 12 matched case-control females. Aggressive, affiliative, and sexual behaviors were measured. RESULTS: MPA-treated females showed less affiliative and sexual behavior compared to matched controls during the breeding season. MPA treatment was associated with decreased aggression emitted toward and received from females during the breeding season. CONCLUSION: MPA treatment is associated with differences in social behavior of female rhesus macaques during the breeding season, when normal hormonal cycles are attenuated by the treatment, but there is no indication that MPA-treated females bring an additional risk for more aggression during the male introduction and breeding season.

Factors influencing the success of male introductions into groups of female rhesus macaques: Introduction technique, male characteristics and female behavior.

In captive populations of rhesus macaques, novel adult males are commonly introduced to female groups every few years to prevent inbreeding, which mimics male dispersal in wild macaque populations. However, introducing adult males is challenging because macaques are aggressive to newcomers, which can result in serious injuries. Efforts to reduce trauma risk during the introduction process and increase the probability of success are needed. Here we investigate the impact of multiple factors, including male attributes (e.g., age, weight, rank, and experience), introduction method (punctuated vs. continual exposure to females), and female behavior, on males' trauma risk and integration success. We studied eight introductions of multimale cohorts (3-7 males each; N = 36 total) into existing female groups of rhesus macaques at the Yerkes National Primate Research Center. Four cohorts were introduced using the punctuated exposure method where adult males were moved each morning from run housing to the females' indoor enclosure and returned to run housing in the afternoon, and four cohorts were introduced using the continual exposure method where adult males were moved to an introduction enclosure attached to the females' outdoor compound, allowing males to live in protected contact next to the female group continuously. Generalized linear mixed models fitted to trauma risk (e.g., latency to first trauma; total trauma count) and success or failure to integrate (i.e., continual residence within the female group for greater than 53% of days within a 28-day window after first overnight stay) showed that continual exposure to females in the introduction enclosure reduced male trauma risk and increased the likelihood of successful integration compared to punctuated exposure. Males received less trauma when they received a higher rate of grooming from females. Male attributes had no effect. These findings highlight the importance of introduction technique and female behavior in the process of males' social integration into female groups.

Influence of female coalitionary aggressive behavior on the success of male introductions to female groups of rhesus macaques (Macaca Mulatta).

Migration patterns of wild rhesus macaque males are often mimicked in captivity by introducing unfamiliar males to female groups every few years. This strategy prevents inbreeding and has been shown to encourage group stability once males are fully integrated. The current study focused on female coalitionary aggressive behavior directed toward males during introductions to describe factors that predict its frequency and any relationship with introduction success. Observational data (755 h) were collected during eight introductions of male cohorts (3-7 individuals) to established female groups (14-39 breeding-age females). Female coalitionary aggression (FCA), defined as four or more females simultaneously attacking an individual male, was recorded 114 times and occurred during all introductions. Data showed that male groups with alpha males who aggressed females during the coalitionary events were more likely to be successfully integrated than those with alpha males who did not retaliate against females. Stepwise multiple regression analyses of individual females (N = 183) revealed that females from larger groups and older females were more likely to be involved in coalitionary aggression, while rank, family size and number of matrilines in the group did not play a role. A rating system of the severity of FCA events revealed male groups receiving more severe FCA were less likely to be successfully introduced, and larger male groups received more severe FCA than did smaller groups of males. Based on these data, it is recommended that colony managers expect FCA to occur during introductions, especially with older females and larger groups. Colony managers should monitor the alpha male's response to FCA, as well as the severity of the FCA since those factors may predict introduction success.

Pair housing of Macaques: A review of partner selection, introduction techniques, monitoring for compatibility, and methods for long-term maintenance of pairs.

Pair housing of macaques has become a widely implemented compromise between meeting the social needs of the monkeys and allowing for their use in biomedical research. While beneficial to the animals, pair housing can provide challenges for those caring for them. Drawing from both scientific literature and direct experience, this paper provides a review of practical aspects of pair housing including partner selection, pairing methodologies, staff education, and equipment considerations. Recommendations include selecting a pairing method appropriate to the facility and the individual animals being paired, educating staff on social behavior, and establishing a pair monitoring program to facilitate long-term pair maintenance. Assessment of behavior is essential in determining the compatibility of new pairs and in identifying established pairs that may need interventions to enhance their long-term compatibility. The pair housing program at the Yerkes National Primate Research Center is described as one model of a successful program. Am. J. Primatol. 79:e22485, 2017. © 2015 Wiley Periodicals, Inc.

Effects of changing housing conditions on mangabey behavior (Cercocebus atys): Spatial density, housing quality, and novelty effects.

The separate influences of spatial density and housing quality on the behavior of captive animals are difficult to measure because the two factors are often intrinsically linked. Here, we recorded affiliative and agonistic behavior in adult sooty mangabeys in various housing situations, testing spatial density and housing quality changes separately (N = 26 experienced spatial density changes; N = 12 experienced housing quality changes). We varied spatial density by 50% while holding housing quality constant and we varied housing quality while holding spatial density constant (achieved by comparing two types of run-housing that varied in the amount of visual privacy and outdoor access). Each housing condition was one month in duration. Prior to collecting data in each housing condition, we evaluated the subjects' initial responses to the change in housing environment during 2-week novelty periods. Affiliative behavior did not change during the novelty periods. Agonistic behavior initially increased slightly when spatial density increased and it decreased significantly when spatial density decreased; it also decreased when subjects moved to housing that offered more visual privacy and outdoor space, indicating that the mangabeys were sensitive to these housing changes. After the novelty periods, affiliative behavior increased under higher spatial density, but remained unchanged across housing quality conditions; agonistic behavior remained unchanged across all conditions. Results suggest that a prolonged increase in spatial density led the mangabeys to adopt a tension-reduction coping strategy, in which the increase in affiliative behavior alleviates a presumed increase in social tension. Reducing visual privacy and choice did not affect the mangabeys' behavior, post-novelty period. Thus, like many other primates, the mangabeys managed tension by flexibly adapting to changes in their housing environment in ways that reduce the risk of severe aggression. This study highlights the importance of controlled behavioral studies in facilitating data-driven management decisions that promote animal welfare. Am. J. Primatol. 77:1001-1014, 2015. © 2015 Wiley Periodicals, Inc.

Rates of reinforcement and measures of compliance in free and protected contact elephant management systems.

Protected contact is an alternative to traditional captive elephant training techniques that emerged as a result of concerns for animal welfare and personnel safety. The present study documented the behavior of elephants and their animal care professionals to determine rates of reinforcement and measures of compliance under two handling systems. Behavioral data were collected from animal care professionals and elephants during the elephants' baths in both free contact (FC) and protected contact (PC). Positive reinforcement, in the form of food, was delivered, on average, nearly eight times more frequently in the PC condition. Further, the mean rate at which the animal care professionals used the ankus in the FC condition as negative reinforcement was similar to the mean rate at which they provided positive reinforcement to the elephants in the FC condition. Latencies between verbal commands and the elephants' behaviors demonstrated an inconsistent pattern, but were generally longer in the PC condition. The mean percent of "refusals" by the elephants was higher for most behaviors across elephants in the PC condition. The findings suggest that animal care professionals did not heavily rely on positive reinforcement in the FC condition to elicit desired behaviors from the elephants, but this was the case in the PC condition. We propose that longer latencies and higher mean percent of refusals by the elephants may indicate that they were exercising choice or control over their environment, which has been associated with improved well-being. Additional studies of this kind are needed to enable other institutions to make informed decisions about elephant management and welfare.

Comparing options for pair housing rhesus macaques using behavioral welfare measures.

In a biomedical research environment, research or management procedures may render continuous full contact pairing of rhesus macaques (Macaca mulatta) unfeasible. This study aimed to determine whether separation on a frequent basis or housing in adjacent cages with tactile contact interferes with the behavioral benefits of continuous full contact. Behavioral data (1260 hours) were collected from 32 adult females and 16 adult males housed at two National Primate Research Centers. Subjects were studied in four housing conditions: single housing, full contact pair housing, intermittent contact pair housing, and protected contact housing. After introduction, each pair was housed in each of the three social housing conditions in varying order. Among females, but not males, introducing animals into full and intermittent contact reduced levels of abnormal behavior. There was a trend toward this reduction in protected contact. In both females and males, full and intermittent contact was associated with lower levels of anxiety-related behavior, but protected contact was not. Females spent more time inactive in protected contact than either full or intermittent contact, and males showed a trend toward less inactivity following introduction into full contact. Both sexes showed less affiliation in protected contact compared to the other forms of social housing. Agonistic behavior among females was not affected by housing condition; among males, levels were equivalent in full and intermittent contact but were higher in intermittent than protected contact. Frequent separation of pairs does not appear to detract from the behavioral benefits of pair housing. Separation by a barrier permitting tactile contact is inferior to other forms of social housing but showed modest improvements over single housing nonetheless. This study can guide the provision of social contact to rhesus macaques under conditions restricting pairs from continuous full contact.

Chimpanzees (Pan troglodytes) in U.S. Zoos, Sanctuaries, and Research Facilities: A Survey-Based Comparison of Species-Typical Behaviors.

A survey was sent to zoos, research facilities, and sanctuaries which housed chimpanzees. Data collected included information about 1122 chimpanzees' age, sex, social group-size, rearing history, and enclosure. Respondents were also asked to indicate if certain behaviors had been observed in each chimpanzee over the prior two years. Species- typical behaviors (STBs) were queried, including copulation, tool-use, nest-building, and social grooming. Tool-use was reported present for 94.3% of the sample (n = 982), active social grooming for 85.7% (n = 1121), copulation for 68.3% (n = 863) and nest-building for 58.9% (n = 982). Of the subjects for whom we had data regarding all four STBs (n = 860), 45.6% were reported to engage in all four. Logistic regression analyses using forward Wald criteria were conducted to determine the best model for each STB based on the predictors of age, sex, rearing history, group-size, facility-type, and a sex-by-rearing interaction. The best model for copulation (χ2(6) = 124.62, p < 0.001) included rearing, group-size, facility-type, and the sex-by-rearing interaction. Chimpanzees were more likely to copulate if they were mother-reared, in larger groups, living in research facilities, and, if not mother-reared (NOTMR), more likely to copulate if they were female. The best model for tool-use retained the predictors of age category, facility-type, and sex-by-rearing (χ2(5) = 55.78, p < 0.001). Chimpanzees were more likely to use tools if they were adult, living in research facilities, and if NOTMR, were female. The best model for nest-building included facility-type and rearing (χ2(3) = 205.71, p < 0.001). Chimpanzees were more likely to build nests if they were MR and if they were living in zoos or in sanctuaries. The best model for active social grooming retained the predictors of age, sex, rearing, and type of facility (χ2(6) = 102.15, p < 0.001). Chimpanzees were more likely to engage in active social grooming if they were immature, female, mother-reared, and living in zoos. This research provides a basic behavioral profile for many chimpanzees living under human care in the United States and allows us to determine potential methods for improving the welfare of these and future chimpanzees in this population.

Benefits of pair housing are consistent across a diverse population of rhesus macaques.

Introducing singly housed rhesus macaques (Macaca mulatta) into isosexual pairs is widely considered to improve welfare. The population of laboratory rhesus macaques is heterogeneous on a variety of factors and there is little literature available to directly evaluate the influence of many of these factors on the benefits of pair housing. Subjects were 46 adult female and 18 adult male rhesus macaques housed at the Tulane National Primate Research Center and the Yerkes National Primate Research Center. Behavioral data totalling 859 h and serum cortisol levels derived from 312 serum samples were analyzed for main effects of housing condition, comparing single housing to pair housing. In addition, a series of analyses were performed to test for interactions between housing condition and seven independent variables: sex, age, prior duration of single housing, presence or absence of a history of self-injurious behavior, and dominance rank, levels of affiliation and agonism in the paired setting. After the collection of 4-8 h of baseline data and three serum cortisol samples, pairs of individuals were introduced to one another and data collection was repeated, no earlier than 4 weeks after introduction. In pair housing both female and male subjects showed decrease in abnormal behavior (females: 54% reduction; P = 0.001; males: 18% reduction; P = 0.0007) and anxiety-related behavior (females: 35% reduction; P = 0.0001; males: 41% reduction; P = 0.0001), and increases in locomotion (females: 41% increase; P = 0.0001; males: 76% increase: P = 0.002). In pair housing, there were no significant sex differences in social behavior. Descriptively, paired females spent 12% of samples engaged in affiliative behavior and 0.5% engaged in agonistic behavior (back-transformed arcsin square root means). The corresponding values for males were 12% and 0.3%. No interaction effects were detected with any of the independent variables tested in this study. Cortisol values varied with sex but did not differ between housing conditions; no differences were detected when any of the above variables were included in the statistical model. Results support the general consensus among those studying the welfare of captive primates that social housing is a potent means for promoting behavioral indicators of the psychological well-being of laboratory primates. These results are of considerable practical significance and include information that refutes common perceptions about the unsuitability of males as socialization candidates, perceived negative.

Predictors of Long-Term Social Compatibility in Rhesus Macaques (Macaca mulatta) Housed in Research Settings.

Social housing improves the well-being of monkeys in research settings; however, little is known about factors influencing the long-term stability of established, full-contact pairs. Archival data were examined to determine whether sex, age, weight, duration pair housed, familiarity, social interruptions, room changes, or sedation events predicted eventual separation of pairs for social incompatibility (n = 80) or for nonsocial reasons (e.g., research or health needs) (n = 1143). Using a logistic regression model (Wald Χ2(8) = 42.325, p < .001), three significant factors were identified. Pairs in which partners had known prior familiarity in group housing were less likely to experience social incompatibility (p = .034). Pairs housed together longer (p < .001) and who staff had temporarily separated through the placement of a cage divider to reduce physical contact were more likely to require permanent separation for social incompatibility (p < .001); additional analysis revealed that dividers were often placed for social reasons, suggesting early signs of social instability. Findings may be useful for primate caregivers when making decisions about managing social partners.

The use of technology to enhance zoological parks.

Technology can be used in a zoological setting to improve visitor experience, increase research opportunities, and enhance animal welfare. Evaluating the quality of these technological innovations and their use by nonhuman and human counterparts is a critical part of extending the uses of technology to enhance animal welfare and visitor experience at zoological parks. Survey data from a small sample of institutions housing primates suggest that computers, television, radio, and sprinklers are the most prevalent types of technological enrichment currently used. Survey respondents were positive about the technology implemented, stating a desire to increase its use.

Female social structure influences, and is influenced by, male introduction and integration success among captive rhesus macaques (Macaca mulatta).

Animal social structure is influenced by multiple socioecological factors. Of these, the links between changes to group demography through the arrival of new individuals and residents' social structure remain unclear. Across seven groups of captive rhesus macaques (Macaca mulatta), we examine how male introductions may be influenced by, and in-turn influence, aspects of female social structure. GLMMs revealed that males integrated more successfully into groups in which females showed more 'despotic' social structures, i.e., higher aggression rates, steeper dominance hierarchies, and greater rank-skew in allogrooming network connectedness. Yet during periods that followed males' social integration, females increased their social tolerance (decreased aggression and shallower hierarchies) and group cohesivity (less clustered allogrooming networks), but retained their tendencies to groom dominants. Our findings, independent of group size and matrilineal relatedness, help better understand how dispersal/immigration may influence social structure, and how assessing changes to social structure may inform macaque welfare and management.

Use of Introduction Enclosures to Integrate Multimale Cohorts into Groups of Female Rhesus Macaques (Macaca mulatta).

Integrating animals into a new group is a challenge for both free-ranging and captive adult male rhesus monkeys (Macaca mulatta), and for females in groups receiving new males. To ensure the genetic viability of the population, however, male transfers must occur in both natural and captive settings. To facilitate the introduction of groups of adult males to adult females, we designed a new enclosure that is attached to the outdoor compound where females are housed. Here we describe the construction of 3 introduction enclosures, their use during 4 introductions of groups of adult males to adult females, a brief comparison of introduction success rates associated with the new introduction enclosures with those of our traditional male introduction method, and a critique by the various groups of staff members working with the new enclosures. Overall, the introduction enclosures benefitted both the macaques and the facility personnel and appear to be a useful enhancement to our process of integrating breeding groups.

Factors facilitating research: a survey of zoo and aquarium professionals.

The purpose of this survey was to assess the background, training, and perceptions of professionals conducting and coordinating research at North American zoos and aquariums accredited by the Association of Zoos and Aquariums (AZA) and to identify the factors they considered critical to successful scientific programs. We analyzed responses to a 57-item questionnaire from 231 professionals at AZA zoos and aquariums. The majority of those surveyed conducted behavioral research, conducted research only in a captive setting, held curatorial positions, had their salaries supported by their institutions' operating budget, and considered themselves part of a successful scientific program. About 30% of those we surveyed possessed a doctoral research degree in comparison to 55% possessing lesser level degrees-19% with master's, 34% with bachelor's, and 2% with other degrees. Support from the chief executive officer and personnel dedicated to conducting scientific programs were judged as the two most important factors contributing to the successful scientific programs. The information provided in this report may be used to develop and improve both established and newly initiated scientific programs in zoos and aquariums.

Habituation and desensitization as methods for reducing fearful behavior in singly housed rhesus macaques.

Operant conditioning using positive reinforcement techniques has been used extensively in the management of nonhuman primates in both zoological and laboratory settings. This research project was intended to test the usefulness of counter-conditioning techniques in reducing the fear-responses of singly housed male rhesus macaques living in the laboratory environment. A total of 18 male rhesus macaques (Macaca mulatta) were selected for this project and randomly assigned to one of three groups: a desensitization training group, a husbandry training group, or a control group. Behavioral data were collected before and after a 6 weeks training and/or habituation period during which the first two groups received a total of 125 min of positive reinforcement training (and also were assumed to undergo habituation to the environment) and the control group experienced only simple habituation to the environment. Based on a Wilcoxon Matched-Pairs Sign Test, we found that a significant proportion of animals exposed to desensitization training showed a reduction in the rate at which they engaged in cringing toward humans (exact significance=0.016, one-tailed, N-ties=6), cringing in general (exact significance=0.016, one-tailed, N-ties=6), and in stress-related behaviors (exact significance=0.016, one-tailed, N-ties=6). This was not the case for animals exposed to basic husbandry training or animals in the control group. A significant proportion of desensitization-exposed animals also showed a reduction in the duration of time spent cringing toward humans (exact significance=0.016, one-tailed, N-ties=6), but not in cringing behaviors in general or in stress-related behaviors. There were not a significant proportion of animals in either the husbandry training group or the control group that showed a decrease in duration of these behaviors. Results of this study could enhance both laboratory animal welfare and laboratory animal research, and could be a first step in developing techniques for reducing fearful behavior in rhesus monkeys in the laboratory environment.

Survey of Behavioral Indices of Welfare in Research Chimpanzees (Pan troglodytes) in the United States.

Chimpanzees demand specialized housing and care and the highest degree of attention to animal welfare. The current project used a survey method to collate information on chimpanzee housing and behavioral indices of welfare across all 6 of the chimpanzee research facilities in the United States. Data were compiled on 701 chimpanzees ranging from 2 to 62 y old (mean age, 26.0 y). All chimpanzees except for one were socially housed; the median group size was 7 animals, and group sizes ranged from 1 to 14. All of the subjects had access to outdoor spaces each day. Daily access to a natural substrate in the chimpanzee's enclosure was available for 63.8% of the subjects. Overall, 94.1% of the chimpanzees used tools to acquire food, 48.1% built nests, 75.8% copulated, and 83.3% initiated grooming bouts. The following atypical behaviors were reported most often: rocking (13.0%), coprophagy (10.0%), and stereotyped behaviors other than rocking (9.4%). There was widespread evi- dence of positive animal training techniques, with nearly all (97.7%) subjects reported to generally voluntarily cooperate with shifting in their enclosure, and 72.2% were reported to present for an injection of anesthetic. We include some comparison between these findings and data describing zoo-housed chimpanzees. In addition, we discuss survey findings in reference to recommendations made by the NIH Working Group on the Use of Chimpanzees in NIH-supported Research. The current survey assessed a larger sample of chimpanzees living under human care than has been published previously. This broad analysis can help to guide future improvements in behavioral management to address behavioral problems or deficits.

Effects of sex and early rearing condition on adult behavior, health, and well-being in captive chimpanzees (Pan troglodytes).

Scientific evaluation of management strategies for captive species is part of the establishment of best practices for animal welfare. Here we report the effects of sex, rearing, and a sex-by-rearing interaction on adult, captive chimpanzees' (Pan troglodytes) behavior, health, well-being, personality, and orientation towards humans based on multiple methods (observation, animal records, and surveys). Chimpanzees raised in three conditions, mother-reared (MR), standard nursery (ST) and an experimental nursery (RC), were assessed approximately 20 years after their differential rearing experiences concluded. Sex had a significant effect on behavior towards conspecifics (aggression [M > F]; affiliation [F > M]), on abnormal behavior (rocking [M > F]), and on likelihood of incurring at least one injury (between ages 6 and 10 [M > F]). Rearing condition had a significant impact on behavior towards humans (negative solicitation [RC = ST > MR = ST]; neutral behavior [RC > ST > MR], yawning (RC = ST > MR = ST), subjective well-being (MR = ST > RC = ST), and on GI illness frequency (RC > ST = MR). Sex interacted with rearing on aggression towards humans (for males, RC > MR = ST), frequency of upper respiratory infection (URI: for males RC > MR = ST)) and likelihood of at least one URI between the ages of 11 and 15 (RC males > ST males). Our findings support the conclusion that there are long-term effects of both early rearing and sex on captive adult chimpanzee welfare.

Systematic assessment of food item preference and reinforcer effectiveness: Enhancements in training laboratory-housed rhesus macaques.

The use of systematic preference assessments can enhance positive reinforcement training with captive animals. We found that the multiple stimulus without replacement (MSWO) technique identified food preferences in laboratory housed rhesus macaques, with raisins and grapes being ranked higher on average than dried apricot, pasta, and green beans (Friedman Test, χ2 (4) = 35.52, p < .001). Agreement between individuals (N = 21) was moderate (Kendall's W = 0.42), and consistency across time varied among individuals (W = .03-.90). Highly preferred items identified by the MSWO assessment were subsequently found to increase subjects' engagement in a husbandry task on which they were being trained (Mann-Whitney U = 6.00, p = .002) and to improve performance on a progressive ratio schedule (Wilcoxon signed-rank test, Z = -2.17, p = .03) when compared with low preference items. The progressive ratio technique supplements other preference assessment techniques by measuring the amount of work a subject will do to gain access to an item. The use of more effective reinforcers identified through systematic assessment has the potential to increase animal performance on husbandry and research tasks and to improve animal welfare in the laboratory setting.