Abstract
The measurement of plasma progesterone concentrations by the radioimmunoassay technique was used to monitor the onset of ovarian activity (puberty) in 19 pubertal heifers and the resumption of postpartum ovarian cyclicity in 25 cows of the N'dama 1 breed. Two or more consecutive plasma progesterone concentrations of not less than 2 nmol L-1 were considered as evidence of ovarian activity. N'dama heifers attained puberty at a mean age and weight of 685 ± 134 days and 172.6 ± 24.5 kg, respectively. Plasma progesterone indicated, however, that the initial oestrous cycles were abnormal and lasted only a few days. Ovarian cyclicity resumed approximately 181 days after parturition. Suckling, however, significantly delayed postpartum ovarian activity (P < 0.05) and prolonged postpartum anoestrus.
