A selenium supplementation study was conducted with Holstein cows to evaluate amounts and methods of administration, namely, oral supplementation (1 vs. 2 mg/head/d, last 60 d of gestation) and intramuscular injection (50 mg at 40 and 20 d prepartum vs. 50 mg at 60, 40, and 20 d prepartum). Blood was collected every 10 d, starting 60 d prepartum and extending 20 d postpartum for cows, and at birth to 20 d for calves. Hair samples of cows were obtained at 60 to 40 and 20 d prepartum, and of the calves at birth. Colostrum samples were obtained for assay. Oral (2 mg/d) and both injection treatments resulted in increased selenium in serum of cows, but selenium in serum of calves at birth was greater only for those whose dams received selenium by injection. Selenium in hair of cows was increased by both injection treatments as well as by the oral treatment of 2 mg/d. Selenium in hair of calves was increased by all methods of administering selenium to the dams. Selenium in colostrum was not affected by any treatment. Thus, pregnant dairy cattle respond to selenium supplementations of a daily oral intake of 2 mg/head/d, the last 60 d of gestation, or by injection of 50 mg each on d 40 and 20 prepartum.