Simultaneous determination of LH activity in blood serum of sheep during three synchronized oestrous cycles by Bio...

LH activity has been in 6 Merino sheep by means of the biological (Bio) and radioimmunological (RIA) test during three subsequent synchronized oestrous cycles. The vaginal sponges were impregnated with 30 mg chlormadinone acetate. The results obtained by the two afore mentioned methods are similar. Oestrous appeared in the average within 96 hours after removal of the sponges. The first increase of LH activity (Bio) was found to occur within 48--72 hours after removal of the sponges (270--400 IU/100 ml serum), the second increase within 15--16 days (450-570 IU/100 ml) and the third within further 16 days (390--590 IU/100 ml serum). The values obtained in the first oestrous cycle by RIA showed an LH peak within 62--110 hours after removal of the sponges (75--90 ng/ml in the second oestrous cycle 86--135 ng/ml and in the third one 58--60 ng/ml serum. In three animals no LH peak could be observed during the first, second or third oestrous cycle. The failure to prove LH peaks in three sheep during different phases of the oestrous cycles is explained by the fact that the synchronization led to heat which, however, did not result in fertile ovulation.