Low respiratory quotients in chow‐fed male bonnet macaque monkeys as an indicator of metabolic stress due to single cage housing

Abstract

ObjectiveDetermine the metabolic affects of previously group housed male monkeys residing in single cage housing (SCH).MethodsAfter two months of SCH, 16 adult male bonnet macaque (M. radiata) monkeys (11.0 ± 1.9 kg, modified BMI = 40.0 ± 7.0 kg/crown‐rump length, m2 and 14.5 ± 3.1 years old) were each placed in the primate Enhanced Metabolic Testing Activity Chamber (EMTAC Inc. Santa Barbara, CA) for 22‐hour measurements of energy intake (kcal/kg) and expenditure (EE; kcal/kg/min), along with the respiratory quotient (RQ;VCO2/VO2). All were fed monkey chow #5038 (LabDiet Inc., Richmond, IN) ad‐libitum under a 12/12 hour light/dark cycle. Metabolic data were divided into day (8‐hours), night (12‐hours) and morning periods (2‐hours). For data analysis (SPSS Ver. 13), monkeys were divided into stressed and non‐stressed groups based on their RQ being above or below 0.70, respectively.ResultsWhen compared to their non‐stressed counterparts, stressed monkeys exhibited a lower 22‐hour mean RQ (0.66 ± 0.03 vs. 0.78 ± 0.05; p<0.05) as well as that during the day (0.69 ± 0.04 vs. 0.81 ± 0.03; p<0.05), dark (0.63 ± 0.02 vs. 0.77 ± 0.07; p<0.05) and morning (0.67 ± 0.03 vs. 0.77 ± 0.07; p<0.05) periods. Moreover, stressed monkeys had a greater EE during the morning period (4.1 ± 0.6 vs. 3.5 ± 0.3 kcal/kg; p<0.05) when compared to their non‐stressed counterparts. Finally, energy intake was reduced in the stressed (7.0 ± 8.5) compared to non‐stressed (27.0 ± 12.2) monkeys.ConclusionBesides the low energy intake, the EMTAC enabled the detection of abnormal metabolic changes associated with the apparent stress of long term SCH.