The Effect of Noise, Vibration, and Light Disturbances from Daily Health Checks on Breeding Performance, Nest Building, and Corticosterone in Mice

Abstract

At our institution, the techniques that technicians use for health checks vary for mice housed in cages on individually ventilated caging (IVC) racks. If the mice cannot be adequately visualized, some technicians partially undock the cage whereas others use an LED flashlight. These actions undoubtedly alter the cage microenvironment, particularly with regard to noise, vibration, and light, which are known to affect multiple welfare and research-related parameters in mice. The central aim of this study was to assess the effects of partial cage undocking and LED flashlight use during daily health checks on fecundity, nest building scores, and hair corticosterone concentrations in C57BL/6J mice to determine the least disturbing method of performing these health checks. In addition, we used an accelerometer, a microphone, and a light meter to measure intracage noise, vibration, and light under each condition. Breeding pairs (n = 100 pairs) were randomly assigned to one of 3 health check groups: partial undocking, LED flashlight, or control (in which mice were observed without any cage manipulation). We hypothesized that mice exposed to a flashlight or cage undocking during daily health checks would have fewer pups, poorer nest building scores, and higher hair corticosterone levels than did the control mice. We found no statistically significant difference in fecundity, nest building scores, or hair corticosterone levels between either experimental group as compared with the control group. However, hair corticosterone levels were significantly affected by the cage height on the rack and the amount of time on study. These results indicate that a short duration, once-daily exposure to partial cage undocking or to an LED flashlight during daily healthy checks does not affect breeding performance or wellbeing, as measured by nest scores and hair corticosterone levels, in C57BL/6J mice.

Figure 1.

Breeding pairs of C57BL/6J mice were randomly assigned to 1 of 3 groups; The partial undocking group (n = 33 breeding pairs), the flashlight group (n = 33), or the control group (n = 34). Cages were either (A) partially undocked so that half the cage length was exposed for 5 s during health checks, (B) exposed to an LED flashlight held 6 in. from the cage front for 5 s, or (C) observed for 5 s without cage interaction.

Figure 2.

Relative spectral power distribution of the LED flashlight used in the study. Curve was drawn based on spectral data provided by the manufacturer. The light is broad spectrum, with peak intensity at approximately 455 nm (blue-appearing light).

Figure 3.

IVC rack that housed the flashlight and control groups. A construction paper barrier, indicated by red dashed line, was installed with masking tape between the flashlight group (left) and the control group (right) to prevent light from the flashlight from reaching control mice.

Figure 4.

Setup of sham cage with environmental monitoring equipment. Microphone was supported by foam that was taped to the cage floor to keep microphone off of the cage floor. Accelerometer was taped to the cage floor so that the base of the accelerometer rested flush to the cage bottom with no bedding between the accelerometer and cage floor. Light sensor rested directly on top of bedding.

Figure 5.

Box plots of various breeding parameters for flashlight use, partial cage undocking, and control cages during daily health checks. (A) The mean breeding index (no. of pups/breeding pair/week) for the control, flashlight, and undocking group were 1.06, 1.07, and 1.05 respectively. No statistically significant differences were detected when comparing the flashlight and control groups (P = 0.91) or the undocking and control groups (P = 0.92). (B) The mean pup weight at weaning for the control, flashlight, and undocking group were 8.9, 8.8, and 8.8 g, respectively. No statistically significant differences were detected when comparing the flashlight and control groups (P = 0.47) or the undocking and control groups (P = 0.51). (C) The mean percentage of litters lost for the control, flashlight, and undocking group were 18.6%, 19.2%, and 21.1% respectively. No statistically significant differences were detected when comparing the flashlight and control groups (P = 0.43) or the undocking and control groups (P = 0.75). Box and whiskers indicate interquartile range, min, and max. Line and ‘x’ indicate median and mean, respectively.

Figure 6.

Box plots of hair corticosterone levels at both 3 and 6 mo time points, comparing flashlight use, partial cage undocking, and control cages during daily health checks. (A) For males, 3 mo hair corticosterone levels (mean = 41 pg/ng) were significantly higher than 6 mo levels (mean = 20 pg/ng, P < 0.001). No statistically significant differences were detected when comparing either experimental group and the control at either 3 mo (flashlight compared with control, P = 0.313; undocking compared with control, P = 0.739) or 6 mo (flashlight compared with control, P = 0.789; undocking compared with control, P = 0.331). (B) For females, 3 mo hair corticosterone levels (mean = 60 pg/ng) were significantly higher than 6 mo levels (mean = 24 pg/ng, P < 0.001). No statistically significant differences were detected when comparing either experimental group with the control group at either 3 mo (flashlight compared with control, P = 0.712; undocking compared with control, P = 0.724) or 6 mo (flashlight compared with control, P = 0.267; undocking compared with control, P = 0.074). Box and whiskers indicate interquartile range, min, and max. Line and ‘x’ indicate median and mean, respectively.

Figure 7.

Bar graphs of mean hair corticosterone levels at both 3 and 6 mo time points, comparing top (rows 1–3), mid (rows 4–7), and low (rows 8–10) rack positions. (A) Male mice in the low rack position had significantly lower corticosterone levels (mean = 19 pg/ng) than the mid position (mean = 37 pg/ng, P = 0.002) and the top position (mean = 66 pg/ng, P < 0.001) at the 3-mo time point. At the 6-mo time point, no statistically significant differences were detected between the low rack position (mean = 21 pg/ng) and either the mid rack position (mean = 20 pg/ng, P = 0.40) or the top rack position (mean = 19 pg/ng, P = 0.29). (B) Female mice in the low rack position had significantly lower corticosterone levels (mean = 27 pg/ng) than those in the mid position (mean = 50 pg/ng, P = 0.015) and the top position (mean = 100 pg/ng, P < 0.001) at the 3-mo time point. At the 6-mo time point, no statistically significant differences were detected between the low rack position (mean = 25 pg/ng) and either the mid rack position (mean = 21 pg/ng, P = 0.10) or the top rack position (mean = 25 pg/ng, P = 0.99). Females (B) had significantly higher corticosterone levels (42 pg/mg ± 38) than did males (A) (31 pg/mg ± 23) (P < 0.001).