| Abstract: | Estrogen and progesterone in milk during the first 21 days of induced and postpartum lactation in Holstein cows and heifers were estimated by assay procedures. Lactation was induced with estradiol-17 beta and progesterone treatment for 7 days. Estrogen and progesterone in induced lactations differed from concentrations in postpartum lactations. In early lactation estrogen was higher in postpartum milk (521 +/- 103 pg/ml on day 1) than in induced milk (336 +/- 46 pg/ml on day 1), but after day 7 the reverse was true (192 +/- 33 pg/ml and 233 +/- 32 pg/ml on day 7). Progesterone remained higher in induced lactation through the first 21 days than in postpartum lactation with the exception of day 19. Progesterone in postpartum milk increased from 4 +/- 1 ng/ml on day 1 to 11 +/- 2 ng/ml on day 21. Progesterone in induced milk showed greater fluctuation (11 +/- 3 ng/ml on day 1 and 22 +/- 9 ng/ml on day 3) but gradually decreased to 12 +/- 2 ng/ml on day 21 (11 +/- 2 ng/ml on day 21 of postpartum lactation). |
