Relationship of mouse body weight and food consumption/wastage to cage shelf level.

The relationships between the shelf level at which mice were housed and body weight and food consumption/wastage were examined by analyzing data obtained from the first 9 months of a carcinogenic dose-response study carried out in 24,192 female BALB/c mice using 2-acetylaminofluorene (2-AAF) as the carcinogen. Each cage, containing four mice, was maintained on a rack at a given shelf level throughout the course of the experiment to allow analysis of data by shelf level. The amount of food removed from each feeder and the body weight of each mouse was measured weekly. Average body weight gain during the first 12 weeks was lowest on the top shelf, highest on the next two shelves, and progressively lower as the shelf approached the lowest level on the rack. Body weights attained by week 36 of the experiment generally reflected this same pattern. Weekly food consumption/wastage, as measured by disappearance of food from the feeder, generally showed the converse shelf-level pattern as that shown by body weight gain. Removal of food from feeders was greatest on the top shelf, lowest on the next shelf, and progressively increased with each succeedingly lower shelf. Although it is not clear whether the food removal pattern was related more to food consumption or food wastage, the observation was reproducible.