Prostaglandin and GnRH analogues - Ovsynch protocol and modifications

Ovsynch protocol

Ovsynch is one of the most “classical” and widely known systems. The protocol consists of two injections of a GnRH analogue separated by a single administration of PGF2α.

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The protocol is mainly targeted at dairy cows.

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Mechanism of action

Prostaglandin administration causes regression of any:

  • accessory corpus luteum
  • luteinised follicle induced by the GnRH
  • corpus luteum present following an earlier spontaneous ovulation.

There are two possible outcomes:

  1. Cows where the fate of the current follicle wave was altered- a new DF should be present on the ovary by the time of the second GnRH.
  2. Cows where the fate of the current follicle wave was altered(GnRH given at the pre-dominance phase of their follicular wave cycle) also have a DF present at the time of the second GnRH.

The ovulatory response in dairy cattle has been tightly synchronised and occurs approximately 26-32 hours after the second GnRH injection. Thus a timed insemination at 17-24 hours after GnRH should result in a high probability of successful conception (Peters et al., 1999).

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Benefits of Ovsynch

Synchronisation is used in cows at all stages of oestrus. Ovsynch ensures an homogenous ovarian follicular status at induction of luteolysis.

As a result the precision of oestrus after prostaglandin-induced luteolysis and the synchrony of the LH surge are improved. Both follicular development and regression of the corpus luteum can thus be synchronized.

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Efficacy of Ovsynch protocol

The ability of GnRH-PGF2α based protocols to effectively synchronise oestrus and ovulation is dependent on the stage of follicular development at the time of initial GnRH injection. Fertility obtained with the Ovsynch protocol is highest when cows ovulate to the first GnRH injection.

For more information see Efficacy studies.

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Modifications of Ovsynch protocol

Ovulatory response to GnRH injection and luteal function following induction of ovulation are dependent on the size of ovarian follicles at the time when GnRH is administered.

Presynchronisation and other modifications of the classical Ovsynch protocol are thought to increase the probability that ovulation will be induced by the first injection of GnRH and that luteolysis and a synchronised ovulation will ensue after administration of prostaglandin and GnRH.

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Co-Synch
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Pre-Synch
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Heat-Synch
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Ovsynch in beef cows

Generally, results obtained with the Ovsynch protocol in beef are lower than in dairy cows. It is mainly associated with a high incidence of post partum anoestrus in beef cows but especially with poor body condition and the presence of a suckling calf.

Although pregnancy rates obtained after single AI in the heat induced with Ovsynch protocol are low in beef cows, they can definitely benefit from the induction of cyclicity and be successfully bred in following cycles.

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Ovsynch protocol and the dose of GnRH used

  1. 8mcg of the potent GnRH analogue, buserelin was used to induce ovulationin the first fundamental studies on the use of GnRh in Ovsynch type systems.
  2. A dose of only 100mcg, gonadorelin was used in later studies.
    This is the norm in the US and has roused interest in many other countries as it offers a possibility for reduction in the cost of treatment. This reduced dose of gonadorelin would represent however a substantial reduction in biological potency because buserelin was estimated to be about 40-200 times more potent than gonadorelin (Chenault et al. 1990).

Since then many authors questioned the efficacy of a reduced gonadorelin dose to induce ovulation, especially in complex Ovsynch type synchronisation systems, where the induction of ovulation in high percentage of cows determines both precision of the synchronisation system and its efficacy. Read more about other studies.

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cows

Ovsynch can be applied to both beef and dairy cows

Ovsynch is one of the most “classical” and widely known systems.