Reproductive steroids in the white-tailed deer (Odocoileus virginianus borealis). I. Seasonal changes in the female

Progesterone and estrogens were measured by radioimmunoassay in 176 serum samples from 15 white-tailed deer during the breeding season and pregnancy. The study spanned two separate years in which some does were serially sampled during both pregnancies. Progesterone levels before the first detected estrus were below! ng/ml except for the period 20 to 11 days before estrus when the level was 1.6 ± 0.98 ng/ml (X ± S.E., N = 4). Estrogen levels were relatively constant at 6.3 ± 0.9 pg/mi (X ± S.E., N = 26) during the fall prior to breeding. Mean progesterone levels were 5.5 ± 0.2 ng/mI (N = 59) during the 1973 pregnancy and 9.3 ± 0.6 ng/ml (N = 34) during the 1975 pregnancy. The levels of progesterone did not change significantly within pregnancy period either year but were significantly different (P<0.001) between years. The level of progesterone was consistent in individual animals within year, but differed significantly between some animals (P<0.005, 1973 and P<0.025, 1975). Progesterone levels tended to be higher when does were carrying more fetuses. Progesterone levels appeared to decline in the animals sampled close to parturition. Estrogen levels increased from 16 ± 12 pg/mi at 12 weeks prepartum to 154 ± 11 pg/mI at parturition. There was no difference between years in estrogen levels. Both estrogen and progesterone levels declined precipitously after parturition. There was no relationship between the number of fetuses carried and estrogen levels