The removal of the persistent CL by enucleation is a widely used treatment which results, in many instances, in restoring the oestrous cycle, although a relatively high incidence of subsequent cystic changes in the ovary has also been reported (Purse & Wickersham, 1969).
Out of about 200 Fresian cows, six were selected in which the cyclic CL persisted for a period of over 30 days. The persistent CL were enucleated per rectum according to the technique of Hammond (1927). Care was taken not to let the CL slip into the ovarian bursa. For 25 days after enucleation, the ovaries were daily examined per rectum, signs of oestrus were recorded, and blood samples were collected. Plasma progesterone was determined by a proteinbinding procedure (Barcikowski & Stupnicki, 1971).
Plasma levels of progesterone before enucleation ranged from 5 to 15