A total of 161 blood samples collected from 77 white-tailed does (Odocoileus virginianus borealis) during the years 1971 through 1974 in Minnesota were utilized to make a preliminary characterization of the estrogen and progesterone levels in pregnant and nonpregnant animals. Progesterone and estrogen were measured by radioimmunoassay. Progesterone levels during the months of December through February were similar for pregnant and nonpregnant animals (3.98 ± 0.57 vs. 5.50 ± 0.82 ng/ml, x̄ ± S.E., N.S., t = 1.51). The pregnant animals had higher progesterone levels during the March through May period (4.61 ± 0.44 vs. 1.94 ± 0.85, P<0.01). Progesterone levels during the months of June to early November, i.e., anestrus, were low and similar for lactating and nonlactating animals. Estrogen levels did not change during the year except for the period just before parturition in the pregnant does when estrogen levels were dramatically elevated (178 ± 29 pg/ml). Two nonpregnant adult does were sampled every 5 days from late January through early March. Progesterone levels exhibited a cyclic pattern of about 28 days duration. Estrogen levels showed no distinct pattern but tended to be inversely related to progesterone. These data suggest that 1) deer exhibit estrous cycles of about 25 to 30 days in length, 2) that estrous cycles recurred in nonpregnant does from November through early March, 3) that progesterone levels are similar for pregnancy and the luteal phase of the estrous cycle and 4) that late pregnancy is characterized by high estrogen levels as compared to early pregnancy and the estrous cycle.
