A metabolism cage for quantitative urine collection and accurate measurement of water balance in adult cats (Felis catus)

Metabolism cages play a pivotal role in nutritional science as they are often used in experiments to determine nutrient requirements of animals, dietary nutrient digestibilities, endogenous excretions, glomerular filtration rates, mineral balance, 24-h urinary excretion rates, etc. Such cages are a convenient way to obtain accurate data on the amount and frequency of excreta produced by animals. The accuracy of the procedures and equipment used for the measurement of excreta production, however, is often neglected, casting doubt on the results obtained. Recently, W amberg et al. (1996b) showed that the recovery of urine collection from mink (Mustela vison) housed in a standard metabolism cage ranged from 68 to 88% in the fed state and 62-78% in the fasted state. This magnitude of under-collection of urine will have a significant impact on data where quantitative urine collection is paramount, such as endogenous urinary excretions, and 24-h urinary excretion rates. The main reason for the incomplete collection of urine in mink was attributed to the cross-contamination of faeces with urine (W amberg et al. 1996b). The domestic cat is a strict carnivore and has been noted to excrete relatively concentrated urine (C hew 1965; A nderson 1982). Under-collection of urine, therefore, has a major impact on the measurement of excretion rates of urinary constituents and any subsequent derived data. The cat, furthermore, has been noted for oliguria, anuria and spraying of urine while held in metabolism cages (W orden et al. 1960; K latt et al. 1975; M atandos and F ranz 1980; R usso et al. 1986), making the domestic cat a difficult animal from which to collect excreta quantitatively. The main objective of this study was to validate quantitative urine collection from cats housed in specially designed metabolism cages fitted with a urine/faeces collection system when fed a nutritionally balanced diet and in the feed-restricted state. Furthermore, the accuracy of water balance measurements using the metabolism cages and urine/faeces collection system was assessed in adult cats.