Dry Bedding Provides Cost-Effective Enrichment for Group-Housed Rhesus Macaques (Macaca mulatta)

In 1998 the National Research Council codified the requirement for providing for the psychologic wellbeing of nonhuman primates used in biomedical research.18 This necessity was strengthened by the performance standards outlined in the eighth edition of the Guide for the Care and Use of Laboratory Animals.19 One goal of enrichment programs is to improve and refine practices that promote behavioral wellness and increase the opportunities for animals to express natural behaviors.19 The environments of captive primates often do not have the types of challenges that primates would find in the wild. Therefore, providing opportunities for animals to express species-specific behaviors in captivity is an important tool to improve their quality of life. Foraging is a behavior that is greatly reduced in captivity. In the wild, nonhuman primates (NHP) spend as much as 70% of their day foraging.15,28,29 In contrast, in captivity, meals are provided at specific times and locations, and animals often spend relatively little time foraging. This lack of foraging opportunities has been posited as a potential cause of overgrooming behavior.5 An enrichment strategy that can help to promote foraging is the use of dry bedding as a substrate. This strategy is particularly important for animals living in cages or in enclosures with a concrete floor. Previous studies in many NHP species have demonstrated the positive effects of providing bedding, including decreased aggression and increased foraging,2,7-10,24 decreased overgrooming,4 decreased labor, and decreased water and chemical usage.18 Still, facilities often encounter obstacles when trying to implement dry bedding. For example, despite the evidence that dry bedding is beneficial to captive primates, its use is perceived as time-intensive and costly; therefore dry bedding is used only infrequently.3 Little information is available on the operational costs of a bedded substrate. One of few studies on this topic examined the use of a bedding substrate in indoor–outdoor group-housed bonnet macaques and found the bedding to be a cost-effective enrichment strategy.6 Although information on the benefits of dry bedding for NHP in cages or in small (that is, fewer than 10 animals) groups is available, few (if any) studies examine dry bedding use for large, outdoor-housed groups. This paucity of information occurred because many NHP facilities in the United State and elsewhere house large groups of macaques in outdoor enclosures with grass or gravel substrate. However, several environmental constraints may direct facilities to house on artificial substrates. Solid flooring provides an opportunity for radiant heating in colder climates. Solid flooring also provides a structure for the controlled disposal of waste through drain-to-sewer systems, thereby decreasing run-off and ground water contamination. Our facility houses approximately 4500 macaques in various types of facilities and social configurations. The 2800 animals of the SPF Indian-origin rhesus macaque breeding colony are maintained in open-top 1-acre corrals and in smaller shelter-housing (SH) units, which are the focus of the current study. Management of breeding colony animals provides opportunity to manipulate the environment to promote enrichment and socialization for the benefit of the NHP health and productivity. The enrichment program for the SH macaques includes social housing; various play structures; seasonal water enrichment (ice blocks, misters, and pools); forage devices that contain fruits, vegetables, and seeds on a rotating schedule; and interaction with caretakers. Prior to the start of the current study, dry bedding was used sparingly as an intervention strategy for groups with social unrest. During times of social stress (that is, group formation, removal or reintroduction of key animals, social instability of unknown etiology), dry bedding was distributed as a distraction to reduce fighting, injuries, and removal of animals. Historic resistance to widespread implementation rested on personnel concerns of increased work load, decreased cleanliness, increased facility-related complications, and a general perception that dry bedding may cause more harm than good (contaminated wounds, eating of wood chips, and so forth). The current study was designed to address these concerns. Animal facilities frequently are designed for economic and ergonomic simplicity.26 The SH units at our facility have concrete surfaces that are easily cleaned with high-pressure water. The daily wash-down of 32 SH units requires substantial water resources that is inconsistent with our facility's philosophy of environmental sustainability. Animal welfare and reduced water usage were strong motivators at the management level to evaluate dry bedding in the SH area. Other authors6 correctly identified the need to involve all stakeholders in the evaluation of costs and benefits of dry bedding to ensure its adoption. Without acceptance by the various teams encountered at the facility, change would be challenged. As is appropriate in assessments of all novel enrichment strategies, addressing the concerns of the participants was an explicit goal of the current study.6,23 Here we examined the use of 2 kinds of wood shavings (pine and pine–aspen mix) in large (30 to 60 animals) outdoor groups of rhesus macaques over a 1-mo period. We focused our study on behavior and operational aspects of management (water use, time to maintain, and so forth). We hypothesized that the presence of wood shavings would increase normal behaviors, decrease abnormal behaviors, and decrease operational costs, including labor.