Decreased blastocyst production in mice exposed to increased rack noise

Abstract

This study was conducted to investigate the possible effect of rack type on the blastocyst yield of mouse embryo donors. The first phase of the study consisted of housing some mice (group A) in a ventilated rack and others (group B) in a static rack in the same room for 3 d, followed by euthanasia for blastocyst collection and corticosterone assay. Parametric tests were used to compare groups. The number of blastocysts per donor was lower in group A (5.0 +/- 1.4 blastocysts) than group B (13.1 +/- 3.7 blastocysts). Mean noise was higher in the ventilated rack (80.4 dBC) than in the static rack (69.2 dBC). Serum corticosterone concentrations did not differ between groups. For the second phase of the study, a third group of mice (group C) was housed in a static rack without a ventilated rack in the same room. The noise level for group C was even lower (45.18 +/- 2.91 dBC), and the blastocyst count per donor (16.4 +/- 2.4) was higher than that of group B. The mean noise levels of empty ventilated and static racks differed significantly between groups for 10 different sound frequencies. Plotting mean blastocyst production against mean rack noise revealed a negative linear relationship with good strength of correlation. These results support the earlier observation that decreased blastocyst count occurs following housing of bred C57BL/6 donor mice in ventilated cages.

Figure 1.

Group comparison of the mean blastocyst counts collected from each donor kept in ventilated (group A) and static (groups B and C) racks. The racks holding groups A and B were held concurrently in the same room; group C was the only rack in the room. The housing period was from acclimation to 96 h after breeding. Each group of 48 mice was allocated into 6 subgroups of 8 mice each; data from each subgroup were pooled and used to generate group means. Overall group mean blastocyst count per donor: group A, 5.0 ± 1.4 blastocysts; group B, 13.1 ± 3.7 blastocysts; group C, 16.4 ± 2.4 blastocysts,Paired Student t tests (P < 0.05; df = 5) revealed significant differences between groups A and B (P = 0.002) and groups B and C (P = 0.002).

Figure 2.

(A) Noise levels (in dBC) measured by a sound-level meter set on C-frequency weighting scale from 4 sites (1, upper left corner; 2, upper right corner; 3, lower left corner; 4, lower right corner) on the racks used to house groups A, B, and C from the acclimation period to 72 h after breeding. Overall group mean noise level: group A, 80.4 ± 1.25 dBC; group B, 69.22 ± 0.88 dBC; group C, 45.18 ± 2.91 dBC. One-way ANOVA revealed significant differences between groups A and B (P = 0.00007) and groups B and C (P = 0.00004). (B) Mean noise levels of empty ventilated and static racks at various frequencies. Noise levels of the ventilated rack (mean, 60.62 ± 12.18 dBC) were significantly (2-way ANOVA, P < 0.05) higher than those of the static rack (mean, 39.24 ± 7.65 dBC).

Figure 3.

Simple linear regression analysis showing negative linear relationship between rack noise level and blastocyst production (r = –0.9013; P = 0.285).

Figure 4.

Corticosterone assays. (A) Percentage of maximal absorbance. Note that most of the absorbance values of groups A (ventilated rack; squares) and B (static rack; triangles) are outside the linearity of the standard curve (circles); only 3 or 4 samples lie within the standard curve's first 3 control sera with the highest corticosterone concentrations. Mean maximal serum corticosterone for groups A (12.07%) and B (11.62%) did not differ significantly (n = 12; df = 11; paired Student T-test). (B) Corticosterone concentrations (pg/mL) of 5 samples each from groups A (mean, 7192.63 pg/mL) and B (mean, 5864.11 pg/mL) whose values were within the linearity of the standard curve. The corticosterone levels of the remaining 7 samples from each group were beyond the upper limit of the standard curve.