Nursery Rearing Methods for Rhesus Macaques

National Primate Research Centers (NPRCs) maintain the majority of their nonhuman primate breeding colonies in species-typical social groups similar to wild species in their natural habitats. This social environment exposes mother reared infants to early complex interactions with other infants, juveniles and adults leading to normal behavioral and physiological development. However, there are situations when it is necessary to remove an infant, such as during a mother’s illness or death, or when an infant’s wellbeing is compromised due to maternal incompetence. Other situations requiring the removal of infants from their dams have occurred during the derivation of a specific pathogen free colonies or when it is required for specific research protocols.

Colony managers remove infants only when necessary because many studies looking at the broad effects of nursery rearing have demonstrated that nursery reared infants are at higher risk of developing abnormal behaviors, such as stereotypic and self-directed behaviors, and may be unable to adapt to living in large social groups due to the lack of appropriate species specific social behaviors. Physiological changes have also been identified within the neuroendocrine system that may affect the regulation of neurotransmitters and hormones that modulate social behaviors, brain architecture development that may affect cognition and emotions, and changes in immune responses that may result in heightened cellular immune function.

Recognizing the differences between nonhuman primate species in addition to the potential challenges that can impact nursery reared infants, breeding colony managers have utilized several different rearing conditions to improve opportunities for orphan socialization and development. When possible, it is ideal to foster orphans to another lactating female which allows the infants to continue with normal species-typical socialization. If fostering is not an option, or is not successful, then nursery rearing becomes a necessity. In general, all orphans are provided with the minimum of an artificial surrogate mother in the form of an inanimate cloth object to provide contact comfort. Research has shown that artificial surrogates capable of multiple directions of movement and oriented so that the infant is in a more natural position, similar to being held by a mother resulted in more normal development of motor skills and exploratory behavior. Research also shows peer rearing, where infants of similar ages are housed together, is beneficial and is commonly utilized in breeding colony nurseries for most species. Strategies for the social management of peer reared infants can involve four different rearing conditions: 1) Continuous pairing, where infants are continuously paired together throughout their development; 2) Intermittent pairing, where peers are allowed to have contact with each other for a limited amount of time, then singly housed for the rest of the time; 3) Continuous rotational pairing, where infants are continuously housed together but have infant partners rotated on a weekly schedule; 4) Intermittent rotational pairing, where infants are paired for a limited amount of time, then housed separately for the rest of the time, and also have rotating infant partners.

Studies have found that providing artificial surrogates, along with continuous rotational pairings as the preferred method to accommodate for the specific needs required in orphan care. The animals reared in this way developed the most normal behaviors, similar to those seen in mother reared infants in socially complex environments. Additional socializations methods used by the NPRCs include supervised “playtime” in which all of the orphans in the nursery were given access to each other in a large modified “play cage” for a specific amount of time. As infants age, the practices for socialization also changes. Following weaning, peer cohorts of orphans can be transitioned to larger housing areas and introduced to adult females and/or males that serve as “mentors” to continue their socialization and development process. While these rearing methods have improved orphan care, breeding colony managers regularly assess rearing options with the goal of providing nursery reared orphans the best opportunity in which to grow, learn, and successfully integrate into larger, complex social groups.


1. Bauer SA, Baker KC, 2016. Persistent effects of peer rearing on abnormal and species-appropriate activities but not social behavior in group-housed rhesus macaques (Macaca mulatta). Comparative Medicine, 66(2): 129-136.

2. Capitanio JP, Mendoza SP, Mason WA Maninger N. 2005. Rearing environment and hypothalamic-pituitary-adrenal regulation in young rhesus monkeys (Macaca mulatta). Developmental Psychobiology. 46: 318-330.

3. Capitanio JP, Mason WA. 2000. Cognitive style: problem solving by rhesus macaques (Macaca mulatta) reared with living or inanimate substitute mothers. Journal of Comparative Psycholoty. 114(2): 115-125.

4. Charmove AS, Rosenblum LA, Harlow HF. 1973. Monkeys (Macaca mulatta) raised only with peers. A pilot study. Animal Behavior, 21(2):316-325.

5. Coe CL, Lubach GR, Schneider ML, Dierschke DJ, Ershler WB. 1992. Early rearing conditions alter immune responses in the developing infant primate. Pediatrics 90:505-509.

6. Dettmer AM, Ruggiero AM, Novak MA, Meyer JS, Suoomi SJ. 2008. Surrogate mobility and orientation affect the early neurobehavioral development of infant rhesus macaques (Macaca mulatta). Developmental Psychobiology, 50(4):418-422.

7. Erwin J, Mitchell G. Maple T. 1973. Abnormal behavior in non-isolate-reared rhesus monkeys. Psychological Reports, 33(2):515-523.

8. Harlow HF, Zimmermann RR. 1959. Affectional response in the infant monkey: orphaned baby monkeys develop a strong and persistent attachment to inanimate surrogate mothers. Science, 130(3373):421-432.

9. Howell BR, Grand AP, McCormack KM, Shi YD, Laprarie JL, Maestripieri D, Styner, MA, Sanchez MM. 2014. Early adverse experience increases emotional reactivity in juvenile rhesus macaques: relation to amygdala volume. Developmental Psychobiology, 56(8): 1735-1746.

10. Lubach GR, Coe CL,Ershier WB. 1995. Effects of early rearing environment on immune responses of infant rhesus monkeys. Brain Behav Immun 9:31-46.

11. Lutz, C, Well, A, Novak, M. (2003). Stereotypic and self-injurious behavior in rhesus macaques: A survey and retrospective analysis of environment and early experience. American Journal of Primatology, 60, 1-15.

12. Lutz, C.K, Novak, mMA. (2005). Environmental enrichment for nonhuman primates: Theory and application. ILAR Journal, 46(2), 178-191.

13. Novak MFSX, Sackett GP. 1997. Pair-rearing infant monkeys (Macaca nemestrina) using a “rotating-peer” strategy. American Journal of Primatology, 41(2): 141-149.

14. Rommeck I, Anderson K, Heagerty A, Cameron A, McCowan B. 2009a. Risk factors and remediation of self-injuries and self-abuse behavior in rhesus macaques. Journal of Applied Animal Welfare Science, 12(1): 61-72.

15. Rommeck I, Gottlieb DH, Strand SC, McCowan B. 2009b. The effects of four nursery rearing strategies on infant behavioral development in rhesus macaques (Macaca mulatta). Journal of the American Association for Laboratory Animal Science, 48(4): 395-401.

16. Rommeck I, Capitanio JP, Strand SC, McCowan B. 2011. Early social experience affects behavioral and physiological responsiveness to stressful conditions in infant rhesus macaques (Macaca mulatta). American Journal of Primatology, 73(7): 692-701.

17. Ruppenthal GC, Walker CG, Sackett GP. 1991. Rearing infant monkeys (Macaca nemestrina) in pairs produces deficient social development compared with rearing in single cages. American Journal of Primatology. 25(2):103-113.

18. Sanchez MM, Hearn EF, Do D. Rilling JK, Herndon JG. 1998. Differential rearing affects corpus callosum size and cognitive function in rhesus monkeys. Brain Res 812:38-49.

19. Sackett GP. 1967. Some persistent effects of different rearing conditions on pre-adult social behavior of monkeys. Journal of Comparative and Physiological Psychology, 64(2):363-365.

20. Sackett G, Ruppenthal G. Elias K. 2006 Nursery rearing of nonhuman primates in the 21st century. New York (NY): Springer Science and Business Media.

21. Worlein JM, Sackett GP. 1997. Social development in nursery-reared pigtailed macaques (Macaca nemestrina). American Journal of Primatology, 41(1) 23-35.

22. Zhang, B. 2017. Consequences of early adverse rearing experience (EARE) on development: insights from non-human primate studies. Zoological Research 38(1): 7-35, 2017.