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

Abstract

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 14d, CIDR out for 16d, 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 (5d 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 (≤9.9mm) and large LF (15.0–19.9mm) on d 14 (CIDR removal) and, as expected, a greater percentage of CIDR-treated heifers were in estrus during the 5d 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 ≥20mm 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±0.6ng/mL, respectively). The percentages of heifers with LF in the smallest category (≤9.9mm) tended to be less (5.3 vs. 16.6%) and the percentage of heifers with LF in the medium-size category (10.0 to 14.9mm) 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 5d 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 14d was an effective method to synchronize an estrous cycle before PGF2α was administered.