Positive reinforcement training affects hematologic and serum chemistry values in captive chimpanzees (Pan troglodytes)

Abstract

Positive reinforcement training (PRT) techniques have received considerable attention for their stress reduction potential in the behavioral management of captive nonhuman primates. However, few published empirical studies have provided physiological data to support this position. To address this issue, PRT techniques were used to train chimpanzees (Pan troglodytes) to voluntarily present a leg for an intramuscular (IM) injection of anesthetic. Hematology and serum chemistry profiles were collected from healthy chimpanzees (n=128) of both sexes and various ages during their routine annual physical examinations over a 7-year period. Specific variables potentially indicative of acute stress (i.e., total white blood cell (WBC) counts, absolute segmented neutrophils (SEG), glucose (GLU) levels, and hematocrit (HCT) levels) were analyzed to determine whether the method used to administer the anesthetic (voluntary present for injection vs. involuntary injection) affected the physiological parameters. Subjects that voluntarily presented for an anesthetic injection had significantly lower mean total WBC counts, SEG, and GLU levels than subjects that were involuntarily anesthetized by more traditional means. Within-subjects analyses revealed the same pattern of results. This is one of the first data sets to objectively demonstrate that PRT for voluntary presentation of IM injections of anesthetic can significantly affect some of the physiological measures correlated with stress responses to chemical restraint in captive chimpanzees.

Testing the Effect of Medical Positive Reinforcement Training on Salivary Cortisol Levels in Bonobos and Orangutans

“…However, the medical PRT does not increase salivary stress hormones and moreover, it can replace much more invasive procedures, such as anesthesia [1], [14], [34]. By establishing a trustful human-ape relationship (apes showing special parts of the body and tolerance to being touched), medical PRT also allows easier interventions such as wound treatment.…”

“…Common husbandry procedures in great apes include, for example: presentation of parts of the body [1], [18], [27], hand injections or venepuncture [27], [34]–[36], collection of blood [35]–[37], collection of urine [1], [24], [36], [38] as well as nail trimming, taking of body temperatures or body weight, and monitoring of heart and respiratory function (reviewed in [12]). In great apes, training has also been used to manage behavior, for example to improve maternal skills in gorillas [25], [39], bonobos [28] and orangutans [40].…”

“…For example, PRT can prevent stress during veterinary procedures and/or increase cooperation in research procedures [1], [14], [34]. It is widely believed that the quality of these interactions during PRT positively affects the well-being of the animal ([41], reviewed in [42]) for example by giving the animals more control over their environment (e.g., [4], [5], [34]). Therefore, PRT is considered to be beneficial and to improve the lives of animals through increased welfare and reduced stress [6].…”

“…One aim of conducting PRT is to establish a relaxed atmosphere that facilitates animal care that, without the training, might be stressful [34], [35]. At the same time, one cannot exclude the possibility that the training itself is a source of stress because, for example, training interferes with other ongoing activities; it exposes subjects to unusually close proximity with human care givers and – in group-living species – may induce competition for attention of the trainer or for access to the reward [43].…”

“…To investigate if medical PRT could reduce stress hormone levels in comparison to otherwise necessary invasive examinations, previous studies have used blood or serum to measure levels of corticosteroids and found that PRT reduced stress during husbandry procedures like caging [46], venepuncture [47], hand injections [34] or blood sampling [9]. While these studies showed that PRT can help to reduce stress in husbandry procedures, the effects of PRT itself on stress in the animals in the training process has so far received little attention.…”