Effect of Hormonal Treatments Prior to Lactation on Hormones in Blood Plasma, Milk, and Urine during Early Lactation

Hormonal changes in blood plasma, colostrum, milk, and urine were studied through day 25 of lactation in 6, 6, and 2 Holsteins, respectively, to compare normal calving, premature calving induced with 25 mg of dexamethasone and estra-dio1-173, and lactation induced with exogenous estradiol-173 and progesterone.Treatments had no effect on concentrations of prolactin in plasma, but concentrations and daily excretion (gg/day) of prolactin were higher in milk after induced calving.Concentrations of prolactin in colostrum were up to 8 times higher than in blood plasma and decreased subsequently to near ratios of 1:1 in milk.Hormonal treatments had no effect on progesterone in plasma, colostrum, or milk.Major differences in the estrogens (estrone, estradiol-173, estradiol-17a, and their total) were observed after day 2 of lactation.Concentrations of the estrogens in plasma and milk, and rates of excretion in urine and milk were lower 3 days after normal calving than after induced calving.Postpartum, estrone decreased proportionately more in milk than estradiol-17a.Proportions of each estrogen in mammary secretions resembled those in blood plasma prior to day 3 of lactation (estrone major) and those in urine thereafter (estradiol-17a major).Concentrations of estradiol-17~ in milk were 3 to 10 times higher, but total estrogen was only about twice higher than in blood plasma.