Two protocols for planned synchronization of estrus and ovulation of 53 heifers and 76 cows, of the Aberdeen Angus cattle breed, bred in Bulgaria, have been studied. The experiment was designed to evaluate the pregnancy rates in beef cattle synchronized under four different protocols of synchronization. The first of the protocols for heifers a group of 13 heifers was under Select Synch protocol with extended period of observation and detection of estrus (6-20 days).In the second group (n-40) was implemented standard PRID-Synch protocol. The first synchronization protocol for 31 cows was a modified standard PRID-Synch with a one-day-earlier treatment with PGF2α (i.m.). In the second group (n-45) a standard PRID-Synch protocol was applied. We found that the total pregnancy rate of the first protocol for heifers was 23 %, and regarding the second protocol it was 25%. In cows we established 61.29% for the first group and 75.56% for second.