A private farm was used to study the postpartum ovarian activity in dairy cows in São Paulo State. Milk samples were collected from 26 animals, twice weekly for one year to monitor the progesterone profile using the radioimmunoassay in detecting the first oestrus in postpartum. The percentage incidence of cows with detectable ovarian activity was 61.1% for animals 31 to 60 days postpartum.
postpartum; dairy cow; progesterone; skim-milk; ovarian activity