Postpartum ovarian activity was evaluated in dairy cows by measuring serum progesterone concentration. In normal Holstein cows, ovarian activity started between day 20 and 30, while it was delayed up to day 40 in abnormal cows.
A solid phase enzyme immunoassy for progesterone determination was developed and evaluated. The correlation coefficinet among serum progesterone concentration as determined by enzyme immunoassy and radioimmunoassy was high (r = 0.866). This technique was used to diagnose early pregnancy by measuring milk progesterone levels 18-25 days post insemination. The overall success rates of the positive or negative pregnancy test were 91.4% and 79.3%, respectively. This study confirms that enzyme immunoassay is a practical and economical method to monitor postpartum cyclicity and to diagnose early pregnancy in cattle. This method eliminates the hazard of using radioisotopes, especially in developing countries.