Evaluation of a Synthetic Bedding Substrate for Mice (Mus musculus)

Abstract

This study compared a synthetic bedding substrate (SBS), which has the potential to be a particulate-free animal bedding system, with the standard woodchip bedding. The objective was to demonstrate that the SBS is habitable for mice and reduces particulates to levels that would not contaminate the eye or potentially induce ocular (corneal) injury. Newly weaned mice were placed in either standard woodchip bedding or SBS. All mice were monitored regarding overall health (appearance, food and water intake, natural behavior, clinical signs, and provoked behavior) to verify their ability to adjust to the bedding. At 8 to 10 wk of age, the mice underwent slit-lamp evaluation for ocular (corneal) abnormalities. Results showed significant differences in body weight and overall health between bedding groups. The incidence of ocular abnormalities did not differ significantly between groups. We conclude that, without modifications and more testing, SBS is not a favorable bedding for mice, and results were inconclusive regarding its use as a bedding to preclude ocular contamination.

Figure 1.

The synthetic bedding substrate (SBS) consists of (a) an absorbent pad below (b) a metal mesh screen that is custom-made to fit a large static cage, (c) polyurethane synthetic beads, and (d) a standard large mouse static cage. The concept is that moisture wicks over the beads, through the wire mesh, and absorbed by the underlying pad, thus keeping mice dry.

Figure 2.

Body weight as the percentage change from the baseline weight, showing that the standard bedding mice had a larger weight increase than the SBS group during the first week of the study. After the first week, the SBS mice gained weight at a similar rate to the standard bedding animals but continued to weigh less throughout the study.

Figure 3.

Clinical health and behavior scores for all mice in each bedding group for the days on which health assessment was completed throughout the study. SBS mice (blue) quickly became wet and unkempt. By day 5, when cage-change interval was decreased to every other day, the mice initially responded positively but soon regressed and began to decline for the rest of the study. The standard bedding mice (red) stayed the same throughout the study and had no health or behavior issues.

Figure 4.

(A) Mice on standard bedding are clean and comfortable, whereas (B) those on SBS are unkempt and uncomfortable in their environment. The SBS mice continued to sleep in groups but preferred not to sleep on the polyurethane beads, instead sleeping on huts to maintain some comfort while resting.

Figure 5.

Slit-lamp photograph. (A) A normal eye, without keratitis or neovascularization. (B) An affected eye with evidence of keratitis (arrow heads) and neovascularization (arrows). Mice with affected eyes confound results and typically are removed from study during ocular research. Magnification, 40×.