CHARACTERIZATION OF OVULATION PERIOD IN C ATTLE AFTER INDUCED LUTEOLYSIS IN DEPENDENCE ON STAGE OF ESTROUS-CYCLE

Prostaglandin F-2 alpha (PGF(2 alpha)) given between day 5 and 14 of e strous cycle induced heat signals in more than 90% of all treated anim als. The portion of animals with complete luteolysis and with LH-Peak increased with longer time intervals between the last estrous and PGF( 2 alpha)-application, Time intervals between PGF(2 alpha)-application and LH-Peak rsp. ovulation was significantly influenced by the day of PGF(2 alpha)-application according to stage of estrous cycle. The mean time intervals between PGF(2 alpha)-application and LH-Peak were 57.0 h, 62.7 h, 76.3 h and 69.5 h when PGF(2 alpha) was given on day 5, 8, 11 or 14 of estrous cycle. On average ovulations were detected 22 h a fter LH-Peak, For fertile heats PGF(2 alpha), should not be given earl ier than on day 8 of estrous cycle. GnRH, given as near as possible to die endogenous LH-Peak, can synchronize ovulations in groups of anima ls. Pregnancy rates were 69.8% in the control group (Al according to h eat signals) and 79% in the group with fixed time insemination. Time i nterval between GnRH-injection acid Al should be 13 hours. This interv al allows capacitation of sperm prior to ovulation and considers the n ecessary time between LH-Peak and ovulation.