Comparison of the CIDR Select and 5-day Select Synch + CIDR protocols that included limited estrus detection and timed insemination for synchronizing estrus in beef heifers

The objective of this study was to compare AI pregnancy rates between the 5-d Select Synch + CIDR (5dCIDR; CIDR = controlled internal drug-release insert) and CIDR Select (CS) programs in replacement beef heifers with a limited period of estrus detection and AI followed by a timed insemination (TAI) of heifers not exhibiting estrus. Crossbred beef heifers (n = 318) were equally and randomly assigned to either the 5dCIDR or CS treatment. The 5dCIDR treatment consisted of gonadotropin-releasing hormone (GnRH) at CIDR insertion, followed 5 d later by CIDR removal and administration of two 25-mg doses of prostaglandin F2α (PGF) administered approximately 12 h apart. The CS treatment consisted of insertion of a CIDR for 14 d, an injection of GnRH 9 d after CIDR removal, and administration of PGF 7 d following GnRH. In both treatments, heifers were detected for estrus for 52 h following PGF, and those exhibiting estrus were inseminated based on the AM/ PM rule. Heifers not observed in estrus were TAI 72 h after PGF, concurrent with GnRH administration. Ten days following TAI, bulls were placed with the heifers for approximately 45 d. Estrus response tended (P = 0.07) to be greater in the CS treatment than in the 5dCIDR treatment. However, conception rate of heifers exhibiting estrus, TAI conception rate, overall AI pregnancy rate, and breeding season pregnancy rate did not differ (P > 0.10) between treatments. In conclusion, 5dCIDR and CS protocols were equally effective at synchronizing estrus in replacement beef heifers.