Synchronization protocols

Definition

A synchronization protocol is a fixed schedule of hormone injections that controls when a cow’s follicle grows, her corpus luteum (CL) regresses and she ovulates, so she can be inseminated at a set time without heat detection. This is timed AI (TAI). Protocols are used for first service after the voluntary waiting period, and to rebreed cows found open (resynch).

Drug classes

Class	What it does in a protocol	Examples (generic)
GnRH (gonadotropin-releasing hormone)	Triggers an LH surge, so a large follicle ovulates (or luteinizes) and a new follicular wave starts	gonadorelin
PGF2α (prostaglandin F2α)	Regresses a mature CL, so progesterone falls and the cow can come into heat and ovulate	dinoprost, cloprostenol
Progesterone (intravaginal insert, CIDR)	Holds progesterone up during the protocol, mainly for cows without a CL (anovular cows) and in heifer protocols	progesterone insert

PGF2α will abort a pregnant cow, so it is given in resynch only after the cow is confirmed open. All products are used under label directions or a veterinarian’s prescription; check each label for milk and meat withdrawal.

The core protocol is Ovsynch. Presynchronization (Presynch, the Pre-Ovsynch half of Double-Ovsynch) is added before it so that more cows start Ovsynch near mid-cycle. Cows that start Ovsynch near mid-cycle ovulate smaller follicles and conceive better to the timed AI than cows started at other stages (Vasconcelos et al. 1999).

Ovsynch (Ovsynch-56)

Day	Time	Step
0	—	GnRH
7	—	PGF2α
8	24 h after first PGF2α	Second PGF2α (optional; improves CL regression)
9	56 h after first PGF2α	GnRH
10	about 16 h after second GnRH	Timed AI

The original Ovsynch gave the second GnRH 48 h after PGF2α and bred 24 h later (Pursley et al. 1995). Cosynch gives GnRH and AI together. Brusveen et al. 2008 found Ovsynch-56 (GnRH at 56 h, AI at 72 h) gave more pregnancies per AI (38.6%) than Cosynch at 48 h (29.2%) or 72 h (25.4%). A meta-analysis of seven trials found that adding the second PGF2α on day 8 raised complete luteal regression by about 12 points and P/AI by about 5 points (Borchardt et al. 2018).

Presynch-Ovsynch

Two PGF2α doses 14 days apart, then Ovsynch starts 10–14 days after the second PGF2α. Moreira et al. 2001 started Ovsynch 12 days after the second PGF2α (Presynch-12), as did the Presynch arm of Souza et al. 2008; Fricke et al. 2003 used 14 days (Presynch-14). Presynch-11 is a field variant that starts Ovsynch 11 days after the second PGF2α.

Presynch-11, counted from the first PGF2α:

Day	Step
0	PGF2α (Presynch 1)
14	PGF2α (Presynch 2)
25	GnRH (Ovsynch starts)
32	PGF2α
33	Second PGF2α (optional)
34, 56 h after PGF2α	GnRH
35, about 16 h later	Timed AI

Herds often start Presynch so that timed AI falls just after the VWP (for example, first PGF2α at about 35–40 DIM for timed AI near 70–75 DIM). Cows seen in heat after a Presynch PGF2α may be bred on that heat and leave the protocol. For reference, Moreira et al. 2001 gave the first Presynch PGF2α at about 37 DIM and started Ovsynch at 63 ± 3 DIM; Fricke et al. 2003 gave Presynch at 32 and 46 DIM and timed AI at 69 ± 3 DIM.

Double-Ovsynch

A Pre-Ovsynch (GnRH, PGF2α 7 days later, GnRH 3 days after that), then 7 days later a full Breeding Ovsynch (Souza et al. 2008). It presynchronizes anovular cows too, which plain PGF2α Presynch cannot.

Day	Step
0	GnRH (Pre-Ovsynch)
7	PGF2α
10	GnRH
17	GnRH (Breeding Ovsynch starts)
24	PGF2α
25	Second PGF2α (optional)
26, 56 h after PGF2α	GnRH
27, about 16 h later	Timed AI

This is the Souza et al. 2008 schedule (they inseminated 16–20 h after the last GnRH; the optional second PGF2α was not part of their trial). The table matches the one on synch compliance.

Resynch

Resynch rebreeds cows that were not seen in heat after an earlier insemination. The first GnRH of Ovsynch is given before the pregnancy check, so open cows are already partway through the protocol when found open. Two common timings, counted from the previous insemination:

Day after AI	Day-32 resynch	Day-25 resynch
GnRH (start)	32	25
Pregnancy check (ultrasound)	39	32
PGF2α to open cows only	39	32
GnRH, 56 h after PGF2α	41	34
Timed AI, about 16 h later	42	35

Pregnant cows stop the protocol at the check (the GnRH they received does not harm the pregnancy). A progesterone insert can be added from the first GnRH to the PGF2α in a resynch or Ovsynch for cows without a CL.

Heifers respond less well to standard Ovsynch; heifer programs commonly use a 5-day protocol with a progesterone insert, or PGF2α and heat detection. See heifer reproduction.

How to pull it in DC305

How a herd records synch steps varies:

Protocol events: one event per injection (or one event that starts a protocol), with the step in the remark. Event names and remark codes vary by herd; map them in the herd’s private dc305-vocab page.
Breeding type code on the BRED event, which marks a service as timed AI vs a detected heat (see breeding type codes).
DC305 protocol lists: some herds set protocols up in DC305 so it schedules each step and prints daily work lists.

Useful pulls:

LIST ID PEN DIM FOR RC=2 LACT>0 DIM=30-45        fresh cows due to start Presynch (adjust to the herd's schedule)
EVENTS BRED ID LACT FOR EDAY>-60                 recent services, with breeding type code
BREDSUM\O FOR LACT>0                             conception by breeding code (timed AI vs heat)

BREDSUM\O is “by breeding code” (see BREDSUM); BREDSUM\XBO crosses times bred with breeding code. DIM=30-45 is an inclusive range.

Protocol compliance (steps given on the right day) is covered on synch compliance.

Typical range

Herd context: US Holsteins, freestall or dry-lot, lactating cows, first pregnancy check by ultrasound at about 28–39 days after AI.

Program	Conception (P/AI) to the timed AI
Ovsynch alone, first service	about 30–40%
Presynch-Ovsynch, first service	about 35–45%
Double-Ovsynch, first service	about 40–50% (higher in first-lactation cows)
Resynch (second and later services)	about 30–40%

The bands bracket the trial results: Ovsynch-56 38.6% overall (Brusveen et al. 2008); Presynch-Ovsynch 41.7% vs Double-Ovsynch 49.7%, with Double-Ovsynch at 65.2% in primiparous cows (Souza et al. 2008, checked at 39–45 days); Presynch-Ovsynch first TAI 31% and resynch 32% overall, 34–38% at days 26–33 (Fricke et al. 2003). Herd results depend on check day, heat stress and compliance.

Interval from AI to rebreeding for open cows: about 35–42 days with a day-25 or day-32 resynch (the timed AI falls on day 35 or 42 in the resynch table above), vs longer if open cows wait for a heat after the check.
Compliance has as much effect as protocol choice; missed or late PGF2α doses lower conception noticeably.

Common mistakes

Comparing protocol conception across herds with different check days. Earlier checks report higher P/AI because of later pregnancy losses.
Not recording the breeding type. Without a timed-AI code, timed and heat services can’t be separated in BREDSUM.
Giving PGF2α before confirming open. In resynch, PGF2α goes only to cows found open at the check.
Shifting the clock. Moving the second GnRH or the AI to fit a shift changes the 56 h / 16 h timing. Write down the actual times.
Breeding heats during a protocol without a rule. Decide whether a cow seen in heat mid-protocol is bred and taken off, and record it, or protocol results get muddled.
Assuming every cow in Presynch responds. PGF2α only works on cows with a CL; anovular cows need GnRH-based presynch or progesterone.