Synchronization Protocols

To make estrus detection more efficient and less time-consuming for staff, hormonal protocols have been implemented into cattle reproductive management.

These hormonal schemes allow heat and ovulation to be synchronized, and in combination with timed artificial insemination (TAI) they render heat detection unnecessary. There is a tendency to inseminate as many cows as possible until the hundredth day after parturition. Early introduction of protocols about 30-40 days postpartum facilitates this, since many can be inseminated as early as possible.

Pharmacological systems used for estrus induction and synchronization in cattle can be divided as follows:

  • Systems that control only luteal function - prostaglandins used alone.
  • Systems that control only follicular function - progestogens used alone.
  • Systems that control both luteal function and follicular dynamics - combinations of prostaglandins and GnRH - combinations of progestogens with gonadotrophins and prostaglandins.


Injection of prostaglandin causes luteolysis and allows for the final growth and maturation of the dominant follicle followed by ovulation at a predictable time post injection.

Estrus synchronization systems based on prostaglandins alone are recommended for:

  • Cycling dairy and beef heifers
  • Cycling dairy cows in good body condition (≥ 3.0)
  • Herds where labor resources for heat detection are limited

Mechanism of Action

  • Injection of prostaglandin at six to 16 days of the cycle (the period of natural prostaglandin F2α release) to induce regression of the CL ending the luteal phase.
  • A new follicular phase begins, and the animal will come into estrus and ovulate.
prostaglandins - treatment schemes

Despite rapid luteolysis the interval to onset of estrus after treatment with PGF2α is variable and dependent on the stage of the follicular development the animal is at when treated.

Because of the variability of estrus and ovulation post PGF2α injection, insemination at detected heat is recommended and gives the best results.

ovulation and insemination time

It is generally accepted that fertility, in terms of conception rates, of the cyclic heifer after prostaglandin treatment is not impaired when compared with untreated control animals inseminated at a natural estrus. However, conception rate in lactating dairy cows following prostaglandin treatment has been inconsistent and is sometimes lower than in control cows inseminated at a natural estrus.

OvSynch Type Systems - Combination of Prostaglandins and GnRH

OvSynch is one of the most “classical” and widely known systems in synchronization protocols. The protocol consists of two injections of a GnRH analogue separated by a single administration of PGF2α1.

classical ovsynch methods


  • Synchronization at all stages of estrus that ensures a homogenous ovarian follicular status at induction of luteolysis.
  • Improved precision of estrus after prostaglandin-induced luteolysis and synchrony of the LH surge.
  • Highest fertility when cows ovulate to the first GnRH injection.
  • Used also as a therapeutic method in many ovarian disorders.

Modifications of the Classical OvSynch

OvSynch is thought to increase the probability that ovulation will be induced by the first injection of GnRH and that luteolysis and synchronized ovulation will ensure that after administration of prostaglandin and GnRH.

Synchronizing Estrus in Dairy Cows

The use of a progestagen device combined with the OvSynch program allows control over both the follicular dynamics and the luteal phase of the cycle. It is an ideal system for herds that wish to tighten and advance the mean calving date as well as maximize pregnancy rates as 100% submission can be achieved.

Replacement Heifter chart

Pre-synchronization of Ovaries with Prostaglandin F2α (PreSynch)

The PreSynch protocol consists of two injections of PGF2α injection 14 days apart, and 12 days prior to initiating the OvSynch protocol.

Pre-synchronization methods are used with OvSynch programs to increase pregnancies per AI. PGF2α is able to synchronize a cycle before the beginning of the OvSynch protocol.

Key points:

  • Increased probability that during the first GnRH injection of the OvSynch protocol, the follicles of the second wave present on the ovary can develop.
  • Increased conception rates in lactating cyclic cows by 18%2.

Double OvSynch

Two OvSynch protocols seven days apart followed by timed artificial insemination (TAI).

Key points:

  • Higher pregnancy rates compared to PreSynch because the two additional doses of GnRH in Double OvSynch stimulates the ovaries to return to activity.
  • No negative consequences in the cows with already active ovaries.
  • More efficient in heifers than in cows.
modifications of classical ovsynch


One of the simplest modifications of the classical OvSynch system used is so called Co-Synch protocol. The second injection of GnRH and AI are performed at the same time. For example, 48 hours after the treatment with prostaglandins.

Key points:

  • Pregnancy rates comparable or only slightly lower than obtained with the OvSynch.
  • Reduced handling of animals3.

Heat Synch

Heat Synch involves replacement of the second GnRH injection with estradiol esters. GnRH and estradiol are injected with one day interval, followed by TAI two days later.

Key points:

  • High precision of the synchronization.
  • Increased behavioral demonstration of estrus in treated cows.
  • Growing considerations about the use of estrogens in food producing animals with no possibility of use in Europe.
modifications of classical ovsynch (2)


When the cows are detected as not pregnant the days between 30 and 32 after the first AI, an effective resynchronization scheme is needed to re-inseminate non-pregnant cows to reduce economic losses4.

Key points:

  • To improve the effectiveness of resynchronization, the use of progesterone devices, another GnRH injection, or shorter hormonal programs are suggested.


  1. Nowicki A, Barański W, Baryczka A, & Janowski T. (2017). OvSynch Protocol and its Modifications in the Reproduction Management of Dairy Cattle Herds - an Update. Journal of veterinary research, 61(3), 329–336.
  2. Moreira F, Orlandi C, Risco CA, Mattos R, Lopes F, Thatcher WW. Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows. J Dairy Sci. 2001 Jul;84(7):1646-59.
  3. Dejarnette JM, Wallace RA, House RB, Salverson RR, Marshall CE. 2001b. Attenuation of premature estrous be havior in postpartum beef cows synchronized to estrus using GnRH and PGF2α. Theriogenology 56:493–501.
  4. Motavalli, T & Dirandeh, Essa & Deldar, Hamid & Colazo, Marcos. (2017). Evaluation of shortened timed-AI protocols for resynchronization of ovulation in multiparous Holstein dairy cows. Theriogenology. 95.