Early post-natal development was studied in experimental Columbian black-tailed deer (Odocoileus hemionus columbianus), with respect to caloric levels of Ideal diets. The growth response, in terms of weight, heart-girth, height-at-withers and length of hind foot, showed that instantaneous relative growth rates were decreased by a decrease in caloric consumption. However, the growth pattern remained the same in the two planes of nutrition employed. The assessment of growth showed that weight and heart-girth similarly reflect nutritive condition and are affected to the greatest extent by caloric intake. Height-at-withers also reflected the planes of nutrition but the length of hind foot showed little difference. Thus a method was outlined for evaluating the degree of fleshiness or nutritive condition by employing the actual weight of the deer or the estimated weight from the heart-girth regression formula and the weight estimated from the hind foot. The index of condition was thus found to be one for normal deer, greater than one for above normal deer and less than one for deer in poor nutritive condition. Blood samples were taken from 20 to 465 days of age showing the changes in some blood constituents with increasing age. Additionally, the blood constituents were analysed with respect to the two planes of nutrition. With the exception of blood glucose and fibrinogen, no demonstrable differences between the two planes occurred. However, all the constituents studied, with the exception of plasma globulin, changed with increasing age. The blood picture presented by the data from these deer are thought to represent a normal condition and may thus be used as a standard in evaluating blood levels of wild Columbian black-tailed deer. / Science, Faculty of / Zoology, Department of / Graduate