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Two groups of 22 heifers were examined rectally for corpus luteum (CL) development. 14 cows from each group with CLs at the 5-16 day stage were injected with prostaglandin F2 alpha (PGF2 alpha ; 25 mg i/m), the remaining 8 in each group were given the same treatment 11 days later. All the heifers were inseminated 80 h after injection. All 22 heifers in group I were examined rectally 35 days after insemination. Open heifers were given a second PGF2 alpha injection if a CL was present and inseminated 80 h later. Open heifers without CLs were injected and inseminated 11 days later. This was repeated every 38-39 days until the end of the experiment (July to December). Heifers in group II were observed for signs of oestrus for 15 minutes twice daily (am and pm) and mated 12 h after the first observed signs. There were no significant differences between the groups for mean days from first service to conception (42.27 and 54.22), mean services/conception (1.68 and 2.22), or pregnancy rate (86.2% and 81.8%). These results suggest that the time required for oestrus detection can be replaced effectively by a scheme for oestrus synchronization and pregnancy diagnosis releasing the dairyman for normal herd management.