For dairy heifers, the 5-day CO-Synch + progesterone-releasing intravaginal device (PRID) protocol is the most widely accepted and used hormonal treatment for timed artificial insemination (TAI). The standard protocol begins with concurrent GnRH and PRID insertion on Day 0; the PRID is removed on Day 5 with prostaglandin F2α (PGF2α) administered at removal, followed by a second PGF2α injection 24 hours later; GnRH is then given concurrently with TAI.Journal of Dair… Administering GnRH concurrent with TAI — rather than 16 hours before — increases pregnancy per AI (P/AI) in dairy heifers.Journal of Dair…

A second PGF2α injection 24 hours after the first improves luteal regression and P/AI in dairy heifers, mirroring the benefit demonstrated in cows.Journal of Dair… Delaying PRID removal by 24 hours beyond the standard protocol decreases premature estrus expression before TAI and improves synchronization efficiency; without this modification, 26.9–33% of heifers express estrus the day before TAI.Journal of Dair…

For the 7-day CIDR protocol in dairy heifers, the EAZI-BREED CIDR Cattle Insert (1.38 g progesterone) is administered for 7 days, with 5 mL LUTALYSE Sterile Solution (dinoprost, 5 mg/mL) injected 1 day prior to CIDR removal on Day 6; animals are observed for estrus on Days 1–3 after removal and inseminated approximately 12 hours after onset of estrus.FDA DailyMed An… A 7-day CIDR protocol with d-cloprostenol on Day 6 and CIDR withdrawal on Day 7 yields P/T of 60.4% in heifers with a corpus luteum (CL) present on Day 0 versus 44.4% in heifers without a CL on Day 0.Veterinary Reco… Dominant follicle size on Day 6 significantly affects outcome: heifers with the largest dominant follicles (16–22 mm) are 5.54 times less likely to be pregnant than those with the smallest dominant follicles (8–10 mm).Veterinary Reco… Inseminating heifers twice (at 48 and 72 hours after CIDR withdrawal) versus once (at 56 hours) does not improve P/T and is not cost-justified.Veterinary Reco…

For the 5-day CO-Synch protocol in beef heifers, all animals receive a CIDR (1.38 g progesterone) and 100 µg GnRH IM on Day 0; the CIDR is removed on Day 5 with PGF2α administered at removal; GnRH (100 µg IM) and TAI are performed 56 hours after CIDR removal.Theriogenology Regarding PGF2α dosing at CIDR removal, a single dose of 25 mg dinoprost IM (1PGF), two concurrent doses totaling 50 mg dinoprost IM (2CO-PGF), and two doses of 25 mg dinoprost IM given 6 hours apart (2PGF) are all established options in this protocol.Theriogenology

For lactating dairy cows, the EAZI-BREED CIDR is used for estrus synchronization by inserting one device per animal and removing it 7 days later, with 5 mL LUTALYSE Sterile Solution administered at the time of removal; animals are observed for estrus on Days 2–5 after removal and inseminated following typical herd practices.FDA DailyMed An… For induction of estrous cycles in anestrous lactating dairy cows, the same 7-day CIDR protocol applies, with insemination at detected estrus on Days 2–5 after removal.FDA DailyMed An… For synchronization of return to estrus in cows inseminated at the immediately preceding estrus, the CIDR is inserted 14 ± 1 days after insemination, removed 7 days later, and cows are observed for estrus on Days 1–3 after removal with insemination approximately 12 hours after onset of estrus; PGF2α must not be administered in this scenario, as it will interrupt a potential pregnancy from the previous insemination.FDA DailyMed An…

Resynchronization of non-pregnant heifers and cows requires protocol selection informed by ovarian ultrasonography at the time of negative pregnancy diagnosis. In dairy cows, the available resynchronization options are classical Ovsynch, modified Ovsynch + PRID (including 2 PGF2α injections 24 hours apart), and the Short Resynch protocol.Journal of Dair… The Short Resynch protocol — consisting of 2 PGF2α injections 24 hours apart, GnRH 32 hours after the last PGF2α, and TAI 16 hours later — is applied to cows with a CL ≥ 15 mm and a follicle ≥ 10 mm on the protocol starting day.Journal of Dair… For heifers specifically, including a CIDR in the resynchronization protocol increases AI2 pregnancy rates compared with no CIDR, whereas no such benefit is seen in cows.Theriogenology The CIDR during resynchronization also increases estrus expression prior to the second AI.Theriogenology

Key factors that reduce P/AI across all progesterone-based protocols include uterine infection, elevated non-esterified fatty acids, and elevated beta-hydroxybutyrate in cows, while anovulatory anestrus and healthy cows are good responders to progesterone-based synchronization.Theriogenology Elevated circulating progesterone concentrations throughout the CIDR protocol (mean 2.82 ± 0.27 ng/mL versus 1.83 ± 0.16 ng/mL) and smaller preovulatory follicle diameter at CIDR removal (4.04 ± 0.44 mm versus 7.21 ± 0.32 mm) are associated with ovulation failure in heifers following a 7-day CIDR protocol.Tropical Animal…

Would you like guidance on presynchronization strategies to improve ovulatory response to the first GnRH in heifers with inconsistent cyclicity?