Physiological indicators of Caribou calf health and compensatory responses to physiological perturbations

Captive husbandry is a cornerstone of modern Caribou (Rangifer tarandus subspecies) conservation (e.g., captive rearing) and research in North America. Husbandry protocols have long emphasized feeding and nutrition programs, but information on health metrics-such as vital signs essential for evaluating animal health-is more limited, especially for young Caribou. We documented vital signs (i.e., body temperature, heart rate, and respiratory rate) of n = 8 hand-reared Caribou calves, each day, from 0 to 23 wk of age. We used multilevel, mixed-effects regression models to evaluate: (i) how vital signs changed as calves grew; and (ii) whether calves compensated (as indicated by changes in vital signs) for physiological perturbations (i.e., changes from homeostasis such as elevated body temperature). We excluded data from 1 calf that had a chronic illness; among healthy, juvenile Caribou in our study, mean (±SE) heart rate was 89 ± 0.7 beats/min, respiratory rate was 19 ± 0.2 breaths/min, and body temperature was 38.9 ± 0.01 °C. Heart rate, respiratory rate, and body temperature decreased as calf age and body mass increased; increasing calf age was a better predictor of heart rate, respiratory rate, and body temperature than body mass. Caribou calves exhibited physiological compensation for increasing body temperature by increasing heart rate and respiratory rate. Heart rate also increased as a function of increasing respiratory rate. Our findings for age-specific vital signs in Caribou calves can serve as baselines for future physiology studies and captive-rearing efforts that may enhance early detection and treatment of illness in captive Caribou.