Studies of hormone patterns during the oestrous cycle of beef cows.

Hormone patterns in blood plasma were examined in relation to the bovine oestrous cycle in two experiments. During the luteal phase LH pulse frequency was low (2-3 pulses per 8 h). There were no consistent correlations between LH, FSH and progesterone concentrations. During luteolysis, falling progesterone concentrations were accompanied by an increase in oestradiol-17 beta concentrations, LH concentrations and LH pulse frequency, the latter being almost one pulse per hour on the day before the preovulatory surge.