Validation of estimating food intake in gray wolves by 22Na turnover

We studied ²²sodium (²²Na) turnover as a means of estimating food intake in 6 captive, adult gray wolves (Canis lupus) (2 F, 4 M) over a 31-day feeding period. Wolves were fed white-tailed deer (Odocoileus virginianus) meat only. Mean mass-specific exchangeable Na pool was 44.8 ± 0.7 mEq/kg; there was no differeence between males and females. Total exchangeable Na was related (r² = 0.85, P < 0.009) to body mass. Overall, ²²Na turnover overestimated Na intake by 9.8 ± 2.4% after 32 days. Actual Na intake was similar in males and females; however, Na turnover (P < 0.05) and the discrepancy (P < 0.01) between turnover and actual Na intake were greater in females than males. From Day 8 to the end of the study, the absolute difference (mEq) between Na intake and Na turnover remained stable. Sodium turnover (mEq/kg/day) was a reliable (r² = 0.91, P < 0.001) estimator of food consumption (g/kg/day) in wolves over a 32-day period. Sampling blood and weighing wolves every 1-4 days permitted identification of several potential sources of error, including changes in size of exchangeable Na pools, exchange of ²²Na with gastrointestinal and bone Na, and rapid loss of the isotope by urinary excretion.