Skim milk progesterone(P₄) profiles in 74 dairy cows were determind to monitor postpartum ovarian activity by radioimmunoassay. Milk samples were collected from each cow every 5 days from 10 to 90 days postpartum. Signs of estrus were observed twice daily, and status of the ovaries and uterus were examined every 10 days by rectal palpation. Results are summarized as follows:
1. Cows were categorized into five types by the change of skim milk P₄ profiles; Type I (normal): Cyclic changes of skim milk P₄profiles appeared within 20 days postpartum(12 cows, 16.2%), Type II (cycle delayed): Cyclic changes of skim milk P₄ profiles appeared from 21 to 60 days postpartum(39 cows, 52.7%), Type III (cycle ceased with low P₄): Onset of the estrous cycle within 20 days postpartum but ceased later with low levels of P₄(7cows, 9.5%), Type IV(cycle ceased with high P₄): Onset of the estrous cycle within 20 days postpartum but ceased later with high levels(>3.0 ng/㎖) of skim milk P₄(4 cows, 5.4%), Type V(acyclicity): Skim milk P₄ concentration remained low((1.0 ng/㎖) until 80 days postpartum(12 cows, 16.2%).
2. Out of the 17 cows classified as the Type III and Type V by skim milk P₄ profiles, 13 cows had inactive ovaries and remaining 6 cows had single or multiple follicular cysts in their ovaries by rectal palpation. All 4 cows of Type IV had a persistent corpus luteum in their ovaries.
3. Approximately eighty percent of the cows had begun ovarian activity by 60 days postpartum and 90.6% by 90 days by skim milk P₄ profiles, but only 39.2% by 60 days and 71.7% by 90 days had shown visible estrus signs. The mean days from parturition to the first, second and third ovulations determined by skim milk P₄profiles was 28.0±11.0, 46.4±13.3 and 66.4±11.5days and the visible estrus signs were 9.3%, 38.1%, and 48.6%, respectively. The mean days from parturition to the first visible estrus was 57.2±15.9 days.
These results indicated that milk P₄profile of each Types by radioimmunoassay can be utilized for monitoring postpartum ovarian and would be useful for the early detection of ovarian dysfunction in dairy cow.
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