Novel Nursery Rearing Strategies
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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.
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