Relationships between time of day, estrous behavior, and the preovulatory luteinizing hormone surge in Holstein cows after treatment with cloprostenol.

Using continuously observed primiparous cows, comparisons were made between cloprostenol-induced and preceding or succeeding spontaneous estruses in a crossover design. There were no significant differences between spontaneous and induced estruses in duration or intensity. In a second experiment, estrus was controlled by administration of two cloprostenol injections, 12 h apart, initiated at 0800 or 2000 h during the midluteal phase. Continuous observation and frequent blood sampling were used to determine relationships between behavior and plasma concentrations of LH and estradiol-17 beta. Relationships between plasma concentrations of estradiol-17 beta and the intensity or duration of estrous behavior were not detected. The intervals from treatment to the onset of estrus and to the LH surge were not affected by time of treatment but were highly correlated. The onset of the LH surge always followed the onset of standing to be mounted by 1 to 2 h. Initiating treatment with cloprostenol at 2000 h resulted in an increased proportion of animals exhibiting onset of estrus and increased mounting behavior at night relative to treatment at 0800 h. For efficient detection of estrus after cloprostenol treatment it is suggested that cloprostenol be administered early in the working day.