The studs wart carried out to find out the changes of hormone levels in blood serum and milk of Holstein cows during the estrous cycle. The progesterone, estradiol-l7β from the b1ood serum and milk samples were assayed by radioimmunoassay methods.
The results of this study were summarized as follows;
1. The progesterone levels in blood serum during the estrous cycles began to decline rapidly at 2 days before estrus, decreased to 0.27±0.18ng/㎖ at on the day of estrus, and reached a peak mean level of 3.33±0.47 ng/㎖ at 15 days after estrus.
2. The progesterone levels in milk during the estrous cycles began to decline rapidly at 2 days before estrus, decreased to 0.80±0.18 ng/㎖ on the day of estrus, and increased a peak mean level of 3.80±0.36 ng/㎖ at 15 days after estrus.
3. The estradiol-17β levels in blood serum during the estrous cycles showed a peak mean level of 9.79±1.72 pg/㎖ on the day of estrus, and decreased from 4.79±1.82 pg/㎖ to 5.73±0.96 pg/㎖ at luteal phase.
4. The estradiol-17βlevels in milk during the estrous cycles showed a peak mean level of 36.80±2.04 pg/㎖ on the day of estrus, and decreased from 18.93±0.84 pg/㎖ to 19.50±1.12pg/㎖ at luteal phase.
5. During 20 to 25 days after artificial insemination, the accuracy of pregnancy diagnosis from the blood serum progesterone levels were 87.5% for non pregnant cows ( <2.0ng/㎖), and 83.3% for pregnant cows (≥3.0 ng/㎖). The accuracy of pregnancy diagnosis from the milk progesterone levels were 75.0% for non-pregnant cows (<2.4 ng/㎖), and 94.4% for pregnant cows (≥3.2 ng/㎖).
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