How do I implement a progesterone-based synchronization protocol for dairy heifers and cows?

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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.1 Administering GnRH concurrent with TAI — rather than 16 hours before — increases pregnancy per AI (P/AI) in dairy heifers.1 A second PGF2α injection 24 hours after the first improves luteal regression and P/AI in dairy heifers, mirroring the benefit demonstrated in cows.1 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.1 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.4 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 0.7 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).7 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.7 For the 5-day CO-Synch protocol in beef heifers, all animals receive a CIDR (1.38 g progesterone) and 100 µg GnRH