BODY-COMPOSITION AND NUTRIENT RESERVES OF ARCTIC CARIBOU

We determined seasonal changes in body mass and composition of arctic caribou (Rangifer tarandus granti) in relation to age and reproductive status. Chemical composition was determined for 37 caribou calves fro m the Central Arctic Herd ranging from 1 to 134 days of age and for 15 adult females collected from the same herd in October, May, and July. Body composition of 5 fetuses from the Central Arctic Herd, 13 calves from the Porcupine Herd, and 10 captive male reindeer (R. t. tarandus ) was determined for comparison. Between October 1989 and May 1990, bo dy fat and protein of adult females declined by maxima of 45 and 29%, respectively; an additional 32% of fat was lost between May and July. Mobilization of large amounts of fat and protein suggests winter under nutrition. Chemical composition and growth patterns of calves did not differ between the herds. The growth rate of Central Arctic Herd calve s was high during the first 28 d post partum (402 g/d), but both growt h rate and fatness declined between 4 and 6 weeks of age (to 306 and - 18.3 g/d, respectively), perhaps in response to insect harassment. Bir th masses of males and females did not differ, but by autumn, male cal ves were 9.1 kg heavier than females. Chemical components (water, fat, protein, ash) were highly correlated with body mass, ingesta-free bod y mass, and carcass mass. Percentages of fat and water were inversely related, but the intercept decreased with age. Marked seasonal hypertr ophy of liver and kidneys was noted in caribou, suggesting the presenc e of mobilizable protein reserves. Seasonal changes in organ masses ma y also reflect variations in metabolic activity and nutrient intake.