Secretion of luteinizing hormone and oestradiol-17β in post partum milked and suckled cows

Abstract

Four milked and four suckled post-partum Friesian cows were used to study LH and oestradiol-17β secretion over the transition from parturition to the resumption of ovarian activity. Plasma samples were collected every 6 h over the first 30 to 40 days post partum and at 15 min intervals for 24 h periods on four occasions at approximately weekly intervals. There were no differences between milked and suckled cows in either duration of the post partum acyclic period or in LH and oestradiol-17β secretion. In cows remaining acyclic for 20 to 40 (mean 28·0 ± 3·5) days post partum compared with those acyclic for 80 to 130 (mean 107·3 ± 13·5) days, LH levels were slightly higher (1·20 ± 0·12 and 0·96 ± 0·10 ng/ml respectively), mean plasma oestradiol-17β levels were higher (1·40 ± 0·13 and 0·80 ± 0·19 pg/ml respectively) and there were significantly more LH episodes (mean 7·50 ± 0·84, range two to 13 24 h and 4·75 ± 0·64, range two to eight/24 h respectively). Plasma oestradiol-17β concentrations often increased following LH episodes, but a significant temporal relationship was not consistently detected. The resumption of ovarian activity was preceded by an increase in basal LH concentrations, the appearance of frequent episodes of LH and enhanced oestradiol-17β secretion.