Vilminot, N. M., Patterson, K. A., Cooper, D. M. et al. 2014. Pharmacokinetics and excreta recovery of [14C]Erioglaucine to determine the impact of solid-bottom compared with wire-bottom caging in Sprague-Dawley rats. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 597 (Abstract #P183).

The Guide recommends the use of solid-bottom caging rather than wire-bottom caging in rodents for many reasons, including reduction in environmental stress, allowance for species-typical behaviors, and decreasing the incidence of pododermatitis and other types of foot lesions. In toxicologic facilities, there often has been a concern for reexposure to test article due to coprophagia when rodents are housed in solid-bottom caging, which is used as a scientific justification for the use of wire-bottom caging. Our IACUC questioned whether housing rats in solid-bottom caging rather than wire-bottom caging would interfere with data interpretation on toxicologic studies. Coprophagia is a normal behavior in rodents that occurs as the fecal pellet is being expelled from the anus rather than while lying on cage bottom floor. Nutritional studies that require complete elimination of coprophagia must use special collars or fecal cups, as wire bottom caging is not sufficient to control the behavior. Furthermore, approximately 10% to 50% of feces are reingested, so even with a test article that is excreted 100% in active form in the feces, at most, this would only increase exposure by 50%. Different dose groups in toxicologic studies are often dosed at 5- to 10-fold dosing intervals, which would likely obscure any variability introduced by reingesting of test article in the feces. To determine the extent to which animals housed in solid-bottom caging are exposed to reingestion of test article compared with animals housed in wire-bottom cages, 2 groups of rats were housed individually in either wire-bottom or solid-bottom, bedded cages. All animals were administered a single dose of [14C]Erioglaucine (FD&C Blue Dye #1) via oral gavage. This compound was chosen because it is largely excreted in the feces unchanged within 36 h of administration. After dose, serial plasma samples and feces samples were collected for radioanalysis. After the final excreta sample collection at 72 h, all animals were euthanized and the residual carcasses were solubilized and analyzed for total radioactivity. Results showed no appreciable difference in either the plasma levels or total carcass recovery of the [14C]Erioglaucine between the 2 groups, indicating that there was no net increase in plasma exposure, or in the amount of test article retained in the gastrointestinal tract from reingested feces for rats housed in solid-bottom, bedded cages compared with those housed in wire-bottom cages. Based on the results from our study, solid-bottom caging has a minimal effect on test article reexposure. Therefore, animals can be housed in solid-bottom caging to provide them with the highest quality husbandry while maintaining scientific integrity. This study did not consider the wide variety of classes of test articles and the different ways in which these test articles may be metabolized. It may be important to consider these variables when designing future studies.