Sync Protocols & Timing

The CIDR (progesterone-releasing intravaginal device) works by maintaining elevated progesterone levels in the cow during the synchronization window. Progesterone suppresses luteinizing hormone (LH) pulsatility, which prevents premature ovulation during the synchronization period. The GnRH injection at insertion creates or synchronizes a follicular wave — depending on where the cow is in her cycle, it either causes ovulation or simply recruits a new cohort of follicles to develop during the CIDR period.

When the CIDR is pulled, the prostaglandin (PGF2α) injection causes luteolysis — it kills the corpus luteum if one is present, dropping progesterone rapidly. The follow-up GnRH injection 48 hours later then drives synchronized ovulation from the dominant follicle that developed during the CIDR period. The goal is to get the entire herd ovulating within a tight window, so that embryo age at transfer (for ET) or insemination timing (for AI) lines up accurately with the cows' actual stage of cycle.

The 7n7 adds an extra seven-day CIDR period before the first GnRH injection. The mechanism advantage: the cow has already been under progestin suppression before GnRH is given, which tends to produce a cleaner follicular wave and tighter ovulation synchrony at the end. Whether that advantage is large enough to justify the extra 7 days and farm visit depends on the program.

The 7-Day protocol is the shorter, simpler option. It works well when the recipient herd is well-managed, known to be cycling, and in good body condition going into synchronization. For producers running tight schedules, the shorter window (17 days for ET, 10 days for AI) reduces the time cattle are under active management.

The 7n7 adds seven days of progestin exposure before the first GnRH. The advantage shows up most clearly in herds where cycling status is less certain — cows that may be in anestrus, early post-partum cows that have not yet resumed cycling, or herds where the nutritional plane has been inconsistent. The extended CIDR window helps bring non-cycling cows into synchrony that the 7-Day would miss entirely.

For ET recipients specifically, where conception rate per recipient directly affects program economics, the tighter ovulation synchrony that 7n7 tends to produce is worth the extra time and visit in programs where the recipient herd quality allows it. In programs with proven cycling recipients in good condition, the 7-Day is often sufficient and the faster turnaround has real operational value.

Protocol selection should be driven by the specific program, not a default preference. I do not run the same protocol on every client — body condition, cycling status, time of year, and program timeline all factor into the recommendation.

Synchronization protocols are precision tools for timing ovulation. They are not a substitution for recipient management. A thin cow with a body condition score below 4.5 will synchronize on paper and fail on transfer day. An acyclic cow that has not resumed estrous cycles post-calving will respond poorly to GnRH regardless of protocol. The protocol cannot manufacture a functioning reproductive tract from one that is not ready.

The variables that protocols cannot fix: body condition (must be addressed 60–90 days pre-breeding), cycling status (teaser bulls should be running 30–60 days before synchronization starts), and structural health of the cow. Recipients that are culled on transfer day because of poor condition or structural problems are wasted synchronization inputs.

The most common reason for disappointing ET results is not the protocol — it is the recipient pool that went into it. Well-managed recipients in rising condition, confirmed cycling, with good structural soundness, give the protocol something to work with. The biology responds differently than when you start from a disadvantaged position.