Effects of prostaglandin F2α administration at CIDR insertion on artificial insemination pregnancy rates in beef heifers

The objective of this experiment was to compare reproductive performance of beef heifers at 5 locations assigned to the 7-d Select Synch + a controlled intravaginal drug release insert (CIDR) and timed-AI (7dSS; n = 297), 5-d Select Synch + CIDR and timed-AI (5dSS; n = 368), or an experimental 7-d estrous synchronization protocol in which PGF2α (PGF) was given at CIDR insertion (Mod; n = 374). On d - 7, the 7dSS treatment received a CIDR and GnRH, whereas the Mod treatment received a CIDR and PGF. On d -5, the Mod treatment received GnRH and the 5dSS treatment received a CIDR and GnRH. On d 0, CIDR were removed and heifers received two 25-mg doses of PGF given 8 h apart. Estrus was detected twice daily for 60 h and heifers detected in estrus were AI by the AM/ PM rule. At 72 h after CIDR removal, heifers not detected in estrus were timed-AI and received GnRH. Estrous response was greater (P < 0.05) in the 7dSS (67.1%) and Mod (69.3%) treatments than the 5dSS (56.1%) treatment. Conception rate of heifers in estrus was greater (P < 0.05) in the 5dSS (62.0%) and Mod (65.6%) treatments than the 7dSS (50.0%) treatment. Conception rate to timed-AI did not differ between treatments (mean = 45.8%). More (P < 0.05) heifers became pregnant to AI in the 5dSS (57.1%) and Mod (58.4%) treatments than the 7dSS (47.3%) treatment. In conclusion, the 5dSS and Mod protocols yielded greater AI pregnancy rates in beef heifers than the 7dSS protocol.