Estrogen Dynamics and Hormonal Differences Associated with Lactational Performance of Cows Induced to Lactate

Abstract

Five nonpregnant and nonlactating Holsteins (three cows and two heifers) were injected subcutaneously each 12 b of days 1 to 7 with estradiol-17β and progesterone (.1mg and .25 mg/day per kg bodyweight) dissolved in absolute ethanol to induce lactation. Estradiol-17β and -17α represented 81 to 89% of total estrogen in blood plasma from days 7 to 27, and -17α was 78 to 90% of total estrogen excreted in urine. Although conversion of absorbed estradiol-17β to free estrone occurred in blood plasma, conversion of estradiol-17β to free estradiol-17α was greater. Among estrogens, only estradiol-17β was higher in blood plasma after day 27 than in some untreated cows with abnormal ovarian function. The heifers, but not the cows, lactated from treatment. Compared with pretreatment (day 0) and end of treatment day 7 to 7.5, concentrations of prolactin in blood plasma were increased prior to first milking (day 12) of heifers as in other studies but were unchanged through day 38 in the cows. Epimers of estradiol, -17β in blood plasma and -17β and -17α in urine, were lower in heifers than in cows during day 13 and days 17 to 26 but not thereafter. However, failure to induce lactation in the cows appeared to be due to low secretion of prolactin.