Søren Wamberg

DAILY MILK INTAKE AND BODY WATER TURNOVER IN SUCKLING MINK (MUSTELA VISON)KITS

Daily (24 h) milk intake and body water turnover were measured in eight litters of suckling mink (Mustela vison) kits (6-9 kits litter-1) during weeks 1-4 post partum using the tritiated water (3HHO) dilution technique. The biological half-life of body water turnover in the mink kits increased linearly from 0.9 days in week 1 (3-5 days post partum) to 1.9 days in week 4 (22-24 days post partum). The daily milk intake varied markedly among the mink kits within a litter and increased significantly with increasing body mass from (mean +/- SEM) 10.9 +/- 0.4 g per kit during week 1 to 27.7 +/- 1.0 g per kit during week 4. Throughout the study, male kits were approximately 10% heavier and had a significantly higher milk intake than female kits. The results were corrected for water recycling between the dam and her kits, ranging from approximately 4 to 15% of the daily milk water intake, and the calculated daily milk yield of the 2 year old lactating mink dams increased from 87 +/- 7 g day-1 in week 1 to 190 +/- 15 g day-1 in week 4 post partum. The average body growth rate of the mink kits ranged from 2.9 g kit-1 per day in week 1 to 5.4 g kit-1 per day in week 4, and the calculated mean intake of mink milk per unit of body weight gain was remarkably stable at 1.0 (g g-1) during weeks 1-3 post partum, but increased to 5.6 (g g-1) in week 4 post partum. The amount of metabolizable energy supplied to the kits by the daily milk yield of the dam increased from approximately 450 to approximately 990 kJ day-1, which corresponded well with the calculated daily energy requirements of the kits. The tritiated water dilution technique was found feasible and reliable for repeated measurements of milk intake in suckling mink kits up to 4 weeks of age.

Effects of feeding and short-term fasting on water and electrolyte turnover in female mink ( Mustela vison )

Daily (24 h) rates of water and electrolyte turnover were measured in a conventional balance study in ten adult female pastel mink (Mustela vison) given free access to a standard mink feed for a 1-week conditioning period, followed by a 4 d experimental period and a 2 d fasting period. Drinking water was available throughout. In addition, the completeness of urine collection and the fraction of urine collected with the faeces were determined using a new experimental technique based on 24 h recoveries of specific urinary markers such as tritiated p-aminohippuric acid ([3H]PAH) or 14C-labelled inulin ([14C]IN) continuously delivered by small Alzet osmotic pumps implanted intraperitoneally. During feeding the mean individual percentage recovery in urine of [3H]PAH released from the osmotic pumps ranged from 68 to 88% (median 78%). The mean percentage of urinary [3H]PAH recovered from faecal collections was 6% (range 3-12%). In response to fasting the mean individual percentage recovery of [3H]PAH in urine ranged from 62 to 78% (median 68%). For urinary [14C]IN the mean percentage recoveries in fed and fasted animals were 79 and 63% respectively. Furthermore, during fasting, withdrawal of the supplies of dietary water caused a slight but insignificant (P = 0.17) increase in the daily intake of drinking water and, hence, the animals maintained their normal water balance by a dramatic reduction in urine excretion (P < 0.001). At the same time urinary solute excretion declined significantly (P < 0.001), due in part to the cessation of dietary electrolyte intake and in part to reduced formation of urea, whereas urinary osmolality decreased only moderately. The mean 24 h balances of Na, K, Ca, Mg, Cl and P were close to zero and only minor differences between the feeding and fasting periods were observed. When corrected for the measured inaccuracies in urine collection the balance data obtained in the present study represent useful reference standards for normally fed and fasted non-growing mink and, to some extent, useful guidelines for future studies in experimental animals.

Nitrogen balance in adult female mink ( Mustela vison ) in response to normal feeding andshort-term fasting

Ten adult female mink (Mustela vison) were studied in a 7 d balance experiment consisting of a 2 d pre-surgery feeding period, followed by surgery, 1 d of recovery 4 d of ad libitum feeding, and a 2 d fasting period. In this experiment (Expt A) the animals had osmotic pumps implanted for continuous release of radioactively-labelled p-aminohippuric acid (p-aminobenzoyl-2-[3H]glycine; [3H]PAH; n 10) and 14C-labelled inulin ([14C]IN; n 5). Repeated 24 h collections of urine, corrected to 100% [3H]PAH or [14C]IN recovery, were used for accurate determination of N balances, 24 h urinary excretion of urea, creatinine, and total N, and calculation of mean 24 h renal clearance rates for endogenous creatinine and inulin. N balances were slightly below zero, but not significantly different between feeding and fasting periods, indicating that correction to 100% [3H]PAH recovery resulted in slight overestimation of the final balances. During fasting, withdrawal of the dietary water and protein loads resulted in a dramatic decline in 24 h urinary volume, and urea and creatinine excretion. Large individual variations in 24 h urinary creatinine excretion (with relative variation coefficients up to 30%) confirmed that this is an unreliable index of the completeness of urine collection. In this respect, recovery rates of [3H]PAH proved far more consistent. Renal clearance values obtained in fed mink were in fair agreement with published data from cats, dogs and ferrets (Mustela putorius furo). Inulin clearance was about 30% higher than endogenous creatinine clearance, although its decline in response to fasting was not significant. In a separate study (Expt B) another ten female mink were equipped with osmotic pumps containing [3H]PAH for determination of 24 h excretion rates of purine derivatives. During feeding, allantoin accounted for more than 97% of the excretion of purine derivatives in urine, uric acid making up less than 2.5%, xanthine and hypoxanthine less than 1%. In fasted animals, urinary excretion of each of these purine derivatives declined to less than 50% of the feeding value. In conclusion, an experimental technique is presented for efficient and accurate measurements of daily urinary excretion of nitrogenous constituents, which allows for correct determination of N balances in adult mink and, presumably, in other mammalian species.

Rates of heat and water loss in female mink (Mustela vison) measured by direct calorimetry

The energy expenditure (EE) of adult female mink was studied by continuous 24-hr measurement of rates of total heat loss (THL) in a controlled environment using a 24 m3 calorimeter allowing separate on-line determination of sensitive (SHL) and evaporative (EHL) heat loss within the range of 20-200 W (72-720 kJ/hr). In four adult female mink (scanblack colour mutant), studied in transparent cages and given free access to feline food pellets and water, the mean 24-hr energy expenditure (= THL) under controlled experimental conditions was 8.9 W/kg (range: 5.5-13.1 W/kg) at 18 degrees C and 5.8 W/kg (range: 4.3-9.5 W/kg) at 24 degrees C. The results are in agreement with the data reported in the literature on the metabolic rate of adult farm-raised mink, calculated from rates of oxygen uptake under controlled experimental conditions, and with the energy requirement for maintenance, 586 kJ/kg/day (6.8 W/kg) recommended by the NRC. Under the experimental conditions of the present study the mean rate of total evaporative water loss (TEWL) amounted to 3.7 g/kg/hr at 18 degrees C and 5.5 g/kg/hr at 24 degrees C. The contributions of SHL and EHL to 24-hr THL in female mink were inversely related and markedly dependent on chamber temperature. When corrected for evaporated urinary and faecal water, SHL and EHL amounted to 76 and 24% of THL at 18 degrees C, but at 24 degrees C the corresponding values were 41 and 59%.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the accuracy of quantitative urine collection in mink (Mustela vison) using osmotic pumps for continuous release of p-amino-hippuric acid and inulin.

A method is described to assess the accuracy of quantitative collection of urine in small experimental animals using implanted Alzetr osmotic pumps for continuous release of specific urinary markers. The nominal pumping rate (10.00±0.15 µl/h; mean±SEM) of 10 osmotic pumps was verified (9.96±0.12 µl/h) in a l0-day in vitro assay in isotonic saline at 39.0 °C. Ten adult female mink (1100±34 g) had a 2-ml osmotic pump implanted intraperitoneally for 7 days while maintained in metabolic cages on a conventional mink diet. In 5 mink the pumps contained [3H]-labelled p-aminohippuric acid (PAH) only. The remaining 5 animals received a pump containing [H]-PAH and [14C]-labelled inulin. The experiment was well tolerated by all animals. In fed animals, the amount of urine collected per day was not influenced by the osmotic pumps, whereas 24 h of fasting (water allowed) caused a dramatic fall in urinary volume. In 4 consecutive 24-h collections of urine (n=l0 animals) the recovery of [3H]-PAH was 70.8±3.6% (range: 52.0-87.2%), and urinary plus faecal water (=total) recovery of [3H]-PAH averaged 77.0±3.7% (range: 60.3%-94.3%). For [14C]-inulin (n=5 animals) the urinary and total recoveries were 68.4±2.2% and 77.2±2.4%, respectively. In urine the 14C to 3H counts-ratio was almost identical to that of the infusion solution, indicating that metabolic decomposition of the markers was negligible. The results indicate that the daily recovery of suitable urinary markers, released by implanted osmotic pumps, provides a reproducible and valid measure of the accuracy achieved in quantitative collection of urine in mink and probably also in other animal species. Hence, this technique may be useful in future studies on animal nutrition and/or drug disposition.