Reproductive Outcomes for Dairy Heifers Treated with Combinations of Prostaglandin F2α, Norgestomet, and Gonadotropin-Releasing Hormone1

We conducted three experiments to test various protocols for synchronizing estrus, ovulation, or both before insemination of heifers. In experiment 1, 23 controls received two PGF2α injections; 23 heifers were treated like the controls plus a norgestomet implant for 8 d, with the second PGF2α injection 24 h before implant removal; and 23 heifers were treated like the previous group plus 100 μg GnRH 54 h after the second PGF2α injection. Although norgestomet and GnRH altered some estrual characteristics, conception rates in experiment 1 (n = 69) and experiment 2 (278 heifers receiving the same treatments as those in experiment 1) generally were not different among treatments. Reproductive outcomes were not improved by adding norgestomet and GnRH to a standard PGF2α protocol. In experiment 3, control heifers received PGF2α and were inseminated after detected estrus or at 72 to 80 h after a second injection of PGF2α given 14 d after the first injection. Select Synch heifers, treated with GnRH either 6 or 7 d before PGF2α, were inseminated after detected estrus, whereas Ovsynch heifers were treated like Select Synch heifers but also received a second GnRH injection approximately 36 h after PGF2α and were inseminated 18 h later. Estrus detection and pregnancy rates after Ovsynch were less than those of controls, whereas conception and pregnancy rates did not differ between control and Select Synch heifers. Therefore, the Select Synch protocol was equivalent to a standard PGF2α protocol, whereas Ovsynch was inferior to both of those protocols.