Ovarian Function and Estrus in Dairy Cows during Early Lactation1

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Abstract
The onset of ovarian function and occurrence of estrus were monitored in two groups of Holstein cows over the first 90 days post-partum. Group 1 consisted of 36 animals housed in a free stall area and observed continuously for estrus with closed circuit television and a time lapse videorecorder. Group 2 consisted of 33 cows housed in tie stalls with estrus detected by the herdsmen. Blood samples were collected twice weekly and assayed for progesterone. The plasma progesterone profiles were used to monitor ovarian function and determine ovulation time. In both groups there was close agreement between basal progesterone concentrations and observed estrous activity. There was no difference between the groups in the incidence of abnormal ovarian activity, or in the interval from parturition to first, second or third ovulation. For all cows with normal ovarian function, the median time to first ovulation was 19.5 days and the time to the second and third ovulation was 44.4 ± 13.2 and 63.7 ± 10.1 days, respectively. A significant difference was observed between the two groups in the days from parturition to first detected estrus: Group 1, 34.5 ± 12.8; Group 2, 56.6 ± 26.5, (P>.01) and in the percentage of cows in which estrus was detected at the first, second and third ovulation: Group 1, 50%, 94% and 100%; Group 2, 20%, 44% and 64%, (P<.01).

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