Follicular populations and luteal function in dairy heifers treated with a controlled internal drug release insert for 14 days as a method to synchronize the estrous cycle before prostaglandin F2α treatment and artificial insemination

Progesterone-containing controlled internal drug release (CIDR) inserts are used to synchronize the estrous cycle before PGF2α is administered for timed AI (14dCIDR-PGF2α program). The program, initially designed for beef cattle, was recently shown to be efficacious in dairy heifers. We hypothesized that the 14-d CIDR treatment would synchronize the estrous cycle in dairy heifers and result in a uniformly sized corpus luteum (CL) and largest follicle (LF) at the time of PGF2α treatment. Holstein (n = 110) or Holstein × Guernsey (n = 4) dairy heifers were assigned to 2 treatments: (1) 14dCIDR-PGF2α [CIDR in for 14 d, CIDR out for 16 d, PGF2α and AI after observed estrus (n = 57)] or (2) control [PGF2α and AI after observed estrus (n = 57)]. Regardless of treatment, additional PGF2α injections were administered at 14-d intervals to heifers that were not seen in estrus. Ovarian ultrasonography and blood sampling were done on d 0 (CIDR administered), 14 (day CIDR removed), 19 (5 d after CIDR removed), 30 (PGF2α administered), and 44 (second PGF2α dose administered to heifers that were not detected in estrus after the first PGF2α). Compared with control (untreated), more CIDR-treated heifers were categorized as having a small CL (≤9.9 mm) and large LF (15.0-19.9 mm) on d 14 (CIDR removal) and, as expected, a greater percentage of CIDR-treated heifers were in estrus during the 5 d after the CIDR removal compared with control heifers (75.4 vs. 22.8%, respectively). On d 19, the CIDR-treated heifers had apparently ovulated based on disappearance of LF and appearance of small CL. On d 30 (PGF2α administration), 89% of 14dCIDR-PGF2α heifers had CL that were ≥20 mm in diameter compared with 55% for control. Presence of larger CL on d 30 was associated with greater concentrations of plasma progesterone in 14dCIDR-PGF2α compared with control (10.5 ± 0.5 vs. 5.0 ± 0.6 ng/mL, respectively). The percentages of heifers with LF in the smallest category (≤9.9 mm) tended to be less (5.3 vs. 16.6%) and the percentage of heifers with LF in the medium-size category (10.0 to 14.9 mm) tended to be greater (84.2 vs. 69.1%) for 14dCIDR-PGF2α versus control, respectively, on d 30. More heifers were detected in estrus within 5 d after the first PGF2α (86.0 vs. 56.1%) and conception rate to AI using sexed semen tended to be greater (61.2% vs. 40.6%) for 14dCIDR-PGF2α compared with control (respectively). Treating dairy heifers with a CIDR for 14 d was an effective method to synchronize an estrous cycle before PGF2α was administered.