Dairy Synchronization: A Learning Experience - Part 2

By Brooke Schultz, Communications Coordinator, CRI

Now that we’ve covered the basics of the dairy cattle estrous cycle (even though it doesn’t really seem that basic at all), let’s leap into the next part of synchronization – Ovsynch.

Ovsynch is used on many dairies. It can be an important ingredient to the success of a reproductive program and has helped make many operations more profitable. This is directly related to Ovsynch enabling producers to get cows inseminated in a timelier manner. We all know your time is precious, so even though you’re taking 10 minutes out of your day to read this, you’ll make up for the lost time tenfold with synchronization.

So, on to the nitty gritty of Ovsynch.

Ovsynch was developed in 1995 (wow, that's 20 years ago already) to increase service rates and improve the overall reproductive efficiency of an operation. It allows a cow to be inseminated without observing signs of estrous and is particularly helpful in situations where heat detection is a challenge.

The term Ovsynch is short for ovulation synchronization (bet you never could have guessed that). The process begins with the administration of GnRH (see Graph 1) which causes ovulation and the start of a new follicular wave (back talking about those waves again - I told you they were important!). Prostaglandin (PGF_2α) is given seven days later and brings about regression of the corpus luteum. Two to three days after the prostaglandin shot (time is dependent on the protocol selected), a final injection of GnRH is given which causes ovulation of the follicle contained in the new follicular wave. Ovulation occurs 24 to 32 hours after the second GnRH. 

Therefore, if working with a group of cows enrolled in this protocol, those that respond will experience synchronized ovulation (makes me think of synchronized swimming); they will all ovulate within an eight-hour period. Insemination is completed at a prescribed time and allows semen to be present as the cows are ovulating. This leads to protocol success.

To break it down just a bit simpler for you:

Ovsynch 56 Steps

1. Initial ovulation is caused by the first GnRH shot.

2. The corpus luteum is regressed on day 7 by the prostaglandin shot.

3. The second ovulation is caused by the final GnRH shot given 56 hours after the prostaglandin.

4. Timed A.I. occurs 16 hours after the final GnRH shot.

What tools can help improve
dairy repro? Magic, of course!
If only magic was synonymous
with science ...

Seems simple enough, right? Don’t worry – we’ve still got more to add to the mix. Only for your benefit, of course.

Lo and behold, there’s something you can do to receive even higher conception rates than just using Ovsynch.

Presynch, short for presynchronization, is a series of injections given prior to administration of the Ovsynch protocol. Presynch, when used in conjunction with Ovsynch, can lead to higher conception rates over Ovsynch alone. The result of this combination is a protocol that is longer than the standard 10-day Ovsynch, and therefore is only recommended for use with first service breedings. What is the cause of this improved fertility? Magic, of course! If only magic was synonymous with science ...

In all seriousness, Presynch is a means of synchronizing the cycles of a group of animals. It places the cows between days five and 10 (see Figure 1) of the estrous cycle prior to administering the Ovsynch protocol. The advantage of grouping cows at this stage of the cycle is the high likelihood these animals will ovulate to the first shot of GnRH at the beginning of Ovsynch. This is the key to the increased fertility. Beginning Ovsynch at any other stage in the cycle results in lower rates of ovulation when GnRH is given.

Various studies have shown that Presynch – Ovsynch protocols increase fertility by approximately 7% to 9% over Ovsynch alone! There are a variety of Presynch options available. Those Presynch methods can be used prior to any of the Ovsynch methods shown on the link.

Stay tuned for the final article in this series. You got it - we'll be focusing on resynchronization!