Early onset of ovarian activity post partum is thought to benefit reproductive performance in dairy cows (e.g. Darwash et al., 1997). However, as in the lactating ewe (Aitken et al., 1995), very early resumption may be detrimental to subsequent conception. An experiment was conducted to determine whether cows commencing ovarian activity very early would be more likely to suffer problems such as prolonged luteal function.

Milk samples were collected from 133 individual multiparous cows three times a week, from approximately one week after calving until the subsequent pregnancy was well established. Profiles of progesterone, measured by ELISA, were used to detect the start of ovarian activity, prolonged luteal function (high values until 24 or more days after the start of ovarian activity or subsequent ovulations), and pregnancy.