Low Respiratory Quotients in chow-fed Male Bonnet Macaque Monkeys as a potential indicator of Metabolic Stress due to single cage housing

Abstract

Background: There is lack of knowledge about specific metabolic changes associated with the stress of long term single cage housing (SCH) of previously indoor group housed male bonnet monkeys (Macaca radiata). Therefore, it is hypothesized that long term SCH will alter the normal metabolic profile of previously indoor group housed male bonnet monkeys. Methods: After two months of indoor SCH, each formally indoor grouped housed male bonnet monkey was placed in the primate Enhanced Metabolic Testing Activity Chamber for 22-hour continuous measurements of energy expenditure (kcal/kg/min) and intake (kcal/kg), along with the respiratory quotient (RQ; VCO2/VO2). For analysis, male bonnet monkeys were divided into two groups, metabolically “stressed” and “non-stressed”, based on 22-hour energy intake being below 13, and above 23 kcal/kg, respectively. Furthermore, the 22-hour metabolic test was divided into an eight-hour day, twelve-hour dark and two-hour morning periods, respectively. Differences (p<0.05) were determined by independent t-tests (SPSS v. 13). Results: Energy intake of the “stressed” monkeys was (p<0.05) lower (4.1 ± 5.6 kcal/kg) in comparison to the “non-stressed” group (27.0 ± 10.5). Furthermore, mean 22-hour RQ was lower (p<0.05) in the “stressed” monkeys (0.68 ± 0.05) in comparison to their “non-stressed” counterparts (0.75 ± 0.08). Finally, compared to their “nonstressed” counterparts, mean RQ’s were lower (p<0.05) for the “stressed” group during both the dark (0.74 ± SD 0.09 vs. 0.65 ± SD 0.05) and morning (0.75 ± 0.08 vs. 0.67 ± 0.05) periods. Conclusions: Two-months of indoor SCH were associated with low RQ’s. This could have implications in regards to results obtained for various drug and physiological studies utilizing monkeys subjected to SCH.