Quantities of immunoreactive estrone and estradiol in blood plasma, urine, and milk were measured during the estrous cycle and pregnancy of cows. The objectives were to develop a radioimmunoassay procedure for quantifying estrogen in milk and urine and to compare changes in milk estrogen with those in blood plasma and urine. Concentrations of estrone and estradiol in milk varied during the estrous cycle. Relative concentrations of estradiol in blood plasma and milk were not different, but average estrone concentrations in milk were four times greater than those in blood plasma. Concentration of total estrogen (estradiol plus estrone) exceeded 1 ng/ml in colostrum and milk from cows milked prepartum, and was correlated with total estrogen in blood plasma and urine before and after calving. Blood plasma estrone was correlated only with milk estrone whereas blood plasma estradiol was correlated with urinary estradiol, milk estrone, and milk estradiol during the estrous cycle. These results raise possibilities that mammary gland of the lactating cow may concentrate preferentially estrone or convert estradiol to estrone. However, estimated excretion of estrogen through the milk represents no more than a fraction of 1% of the total excreted during the estrous cycle, and the proportion becomes less as gestation progresses up to at least 7 mo.

No abstract

No abstract

Concentrations of progesterone, estrogen, and prolactin in plasma were compared among lactations induced in 29 cows by daily subcutaneous injections of .25 mg progesterone and .1 mg estradiol-17beta per kg body weight for 7 days. Superior, median, and inferior lactations were identified by ranking both weightage adjusted maximum milk yields in 7 consecutive days (average 144 +/- 9 kg) and days for milk yield to increase from 5 to 10 kg/day (15 +/- 3 days). Superior and inferior of the former averaged 189 and 101 kg, and their latter averaged 2 and 42 days. Plasma hormones were measured on day 0 before first treatment (day 1), and on days 7, 14, 17, 21, 24, 28, and 35. Superior lactations were associated with below-average progesterone and estrogen in plasma on day 0, rapid decreases in progesterone after day 7 and in estrogen after day 14, and increased prolactin after 7. In comparison, median lactations were associated with elevated progesterone and estrogen after day 17, but prolactin was similar to that of superior lactations. Inferior lactations were associated with decreased prolactin in plasma from days 21 to 35. We hypothesized that (a) first treatment should start 3 to 8 days after estrus, (b) daily doses of estradiol-17beta should be decreased with progesterone unchanged for the 7 days, and (c) estradiol-17beta alone should be continued for 7 days to improve hormonally induced lactations.

Prolactin and growth hormone were measured in blood plasma at 30-min intervals for three consecutive 24-h periods in 6 cows during midlactation. Concentrations of prolactin in milk and yields of milk also were quantified. Prolactin in blood plasma appeared to have a 24-h rhythm as well asd a 6-h rhythm by time series spectral analysis. Lowest prolactin occurred between 0600 and 0900 h each day, whereas maximums occurred between 1030 and 1600 h. Neither milk prolactin concentration nor yield of milk differed between milkings at 0530 and 1730 h. Concentration of prolactin in milk was not significantly correlated with prolactin concentration of plasma. However, prolactin of plasma averaged over the 12-h prior to milking was associated significantly with yield of milk and with total quantity of milk prolactin removed at that milking.