Acceptable pregnancy rates (PR) after timed AI (TAI) could improve reproductive management of dairy heifers. In beef cattle (Helser, 2006) the CIDR/OvSynch TAI protocol was improved by reducing the interval between GnRH and PGF to five days, giving two injections (AM/PM) of PG F and administering GnRH and TAI at 72 h after withdrawal of the CIDR to increase the proestrus period. The overall PR was 65.3%. Using this procedure in dairy heifers, PR was 58.3% at day 32 post TAI (Thatcher, 2007). Objectives of Exp. 1 were to compare PR of dairy heifers relative to whether one vs. two injections of PGF is required for effective use of the CIDR/OvSynch TAI protocol, and to compare PRs to CIDR/OvSynch TAI resynchronization programs of non-pregnant heifers involving estrus and no estrus detection. A second objective was to evaluate PR in two additional groups of heifers using the CIDR/OvSynchTAI protocol with one injection of PGF for first and second service without estrus detection (Exp. 2).
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