Abstract Controlled internal drug release devices (CIDRs) are a reproductive tool in beef production systems to improve efficiency and maximize conception rates by artificial insemination (AI). Estrus synchronization using CIDRs vary in length, injections given, and time to inseminate. Thus, the objective of this study was to compare a 14-d vs 6-d CIDR program on estrus expression and conception rates. Crossbred Angus heifers (n = 78 heifers) approximately 14 months of age were stratified into two treatments. Treatment groups included different breeding protocols where CIDRs were placed for 14 d or 6 d. For the 14-d protocol, CIDRs were placed and a simultaneous intramuscular injection of prostaglandin F2α (PGF) given and 7 days later an intramuscular injection of gonadorelin (GnRH). For the 6-d protocol, heifers received the CIDR and an intramuscular injection of GnRH. All CIDRs were removed 7 d following the GnRH injection and an estrus detection patch (Estrotect® patch, Rockway Inc., Spring Valley, WI) placed on the tailhead of all cattle and an intramuscular PGF injection was administered. Heifers were monitored for signs of heat and inseminated following an AM-PM rule using sex-sorted semen from a single sire. Pregnancy by AI was determined on day 30 of pregnancy and overall pregnancy rates were determined on day 100 of pregnancy. Statistical analyses were performed using SAS 9.4®. The MIXED procedure was used for the effect of 6-d or 14-d protocol on time from CIDR removal until signs of estrus were shown, and time from CIDR removal until heifers were bred by AI. The GLIMMIX procedure was used for the effect of 6-d or 14-d protocol on AI conception rates, overall pregnancy rates, and maintenance of AI pregnancy. Heifers that received the 14-d CIDR exhibited estrus sooner than heifers receiving the 6-d CIDR (38.25 hours vs. 41.11 hours, respectively; P = 0.0461). Heifers that received the 14-d CIDR were bred by AI approximately 7.64 hours sooner compared to heifers receiving the 6-d CIDR (51.38 hours vs. 59.03 hours, respectively; P 0.0001). There were no differences for AI conception rates and overall pregnancies between treatments (P = 0.2661 and P = 0.1618), but they were numerically greater in heifers receiving the 6-d CIDR (61.55% and 94.88%, respectively) compared to the 14-d CIDR (48.72% and 84.64%, respectively). No differences were found between CIDR protocols for maintaining AI pregnancies (P = 0.3541), but it was numerically greater in heifers that received the 6-d CIDR compared to the 14-d CIDR (59.07% vs. 48.65%, respectively). There was no treatment effect on pregnancies, but differences seen in the time from removal of a CIDR until estrus expression and breeding warrant future research to investigate the different synchronization protocols.
Becerra et al. (Wed,) studied this question.