Accuracy of quantitative collection of urine in carnivores.

In studies of animal nutrition, complete 24-h collections of urine samples are often required for detailed analysis and interpretation of urinary excretion of dietary and metabolic constituents. Most reports include a detailed description of the experimental techniques and the equipment used. However, to our knowledge, there is no information available on the completeness of daily urine collection in animal species commonly used for scientific purposes (Wamberg et al. 1996a and 1996c). In strictly carnivorous mammals, such as cats, ferrets (Mustela putorius furo) and mink (Mustela vison), accurate collection of urine is extremely difficult because of their habit of squirting and spreading the urine all over the cage and on top of the feces. Furthermore, due to the excretion of a highly concentrated urine with a high nitrogen content, incomplete collection of urine may lead to overestimation of nitrogen balances and, hence, of the true protein requirements of these animals (Elnif 1992, Tauson et al. 1997). This study was designed to assess the accuracy of quantitative urine collection in conscious female mink by repeated measurements of the recovery, in 24-h urine collections, of two well-documented, radioactively labeled urinary markers, [H]-p-aminohippuric acid (H-PAH) and [C]-inulin (CIN), continuously released, for a period of 8 d, by small osmotic pumps implanted intraperitoneally. Details of the experimental procedure and the results obtained on water, electrolyte and nitrogen turnover during six consecutive 24-h balance periods in mink are reported elsewhere (Tauson et al. 1997, Wamberg et al. 1996c). Materials and methods. In vitro assay. Ten osmotic pumps (Alzet model 2ML1, Alza, Palo Alto, CA), were filled with 2 mL of isotonic (0.154 mol/L) saline containing HPAH (see below) and submerged in sterile isotonic saline in a thermostat-controlled water bath at 39.0 6 0.1°C (Wamberg et al. 1996a). Each pump was mounted with a 5-cm long PE-60 polyethylene catheter leading to a small collecting vial, which was replaced every 24 h. At the end of d 10, the radioactivity of the vials was determined as described below, and the in vitro pumping rate of the osmotic pumps was calculated from the counts-ratio between the daily output collected in the vials and the stock solution with which the pumps were filled initially. Details of the construction and function of the osmotic pumps (Fig. 1) are given by Theeuwes and Yum (1976). In vivo study. In this study, the conventional balance technique that uses metabolism cages designed for mink (Elnif 1992, Glem-Hansen 1980) was improved by the application of a new technique for assessing the completeness of urine collection in small animals (Wamberg et al. 1996a) based on daily measurements of the recovery in urine of two urinary markers, H-PAH and C-IN, which are rapidly and efficiently excreted by the kidneys (Levinsky and Levy 1973). Animals and surgical procedures. Ten adult female mink, pastel color type, weighing Ç1100 g, were housed in metabolic cages in a controlled environment (10-h light:14-h dark cycle and temperature 16 6 1°C) in our laboratory and fed a conventional mink diet, based on industrial fish and slaughterhouse offal, for 1 wk (d –7 to –1) before the experiment. The diet contained (g/kg): dry matter (DM), 310; crude protein, 180; crude fat, 40; and metabolizable energy, 15 MJ/kg DM (Wamberg et al. 1996c). All animals were given free access to drinking water throughout the study. On d 0, the animals were anesthetized, using ketamine hydrochloride, 40 mg/kg intramuscularly (Ketaminol Vet, 50 mg/mL, Veterinaria AG, Zürich, Switzerland), and midazolam hydrochloride, 2.0 mg/kg intramuscularly (Dormicum, 5 mg/mL, Hoffman La-Roche AG, Basel, Switzerland) as described by Wamberg et al. (1996b); a 2-mL osmotic pump (same as those tested in vitro) was implanted intraperitoneally. In five mink, the osmotic pumps contained an accurately weighed amount of sterile isotonic saline with 1.85 MBq of H-PAH; in the remaining five mink, the pumps contained isotonic saline with 1.85 MBq of H-PAH and 925kBq C-IN, to be released in the body over the next 8 d. On d 1, the animals were given free access to food 1 Presented as part of the Waltham International Symposium on Pet Nutrition and Health in the 21st Century, Orlando, FL, May 26–29, 1997. Guest editors for the symposium publication were Ivan Burger, Waltham Centre for Pet Nutrition, Leicestershire, UK and D’Ann Finley, University of California, Davis. 2 Supported by the Danish Agricultural and Veterinary Research Council, grants 13–4905 and 13–4906. 3 To whom correspondence should be addressed. 4 Abbreviations used:C-IN, [C]-labeled inulin; H-PAH, [H]-labeled p-aminohippuric acid; DM, dry matter.