Effects of Extruded Compared with Pelleted Diets on Laboratory Mice Housed in Individually Ventilated Cages and the Cage Environment

The physical form of the diet fed to laboratory animals should be evaluated to reduce experimental variations and confoundingfactors. This 14-d study evaluated the effects of diet form (pelleted or extruded) on intracage ammonia concentrations,feed disappearance, body weight, cage weight, and the degree of cage soilage and whether these effects were influenced bystrain or stock or sex. Mice (C57BL/6, ICR, and nude; age, 4 wk) were randomly assigned to 4 treatment groups representingpelleted and extruded diets from each of 2 vendors (pelleted diet groups, P1 and P2; extruded diet groups, E1 and E2).Intracage ammonia concentrations depended on strain or stock, diet, and day and were higher in cages housing nude micethat consumed P1. Diet type did not affect the weight of mice at the end of the study. Feed disappearance was dependent ondiet type and mouse strain or stock and was greatest in the cages of mice that consumed P1. In addition, the greatest feeddisappearance was seen with ICR mice, whereas the least was seen with C57BL/6 mice. Cages housing male nude mice hadgreater cage soilage than those housing female nude mice. The degree of cage soilage was influenced by diet type and dayalso. These results show that diet form and mouse strain or stock significantly affect intracage ammonia concentrations, feeddisappearance, cage weight, and the degree of cage soilage.