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Virginia Cooperative Extension - Knowledge for the CommonWealth

Eliminating heat detection with an Ovsynch or Pre-Synch program may be the answer to an efficient reproductive program

Dairy Pipeline: November 2001

Ray L. Nebel, Extension Dairy Scientist,
Reproductive Management

The most recent state averages for Virginia DHI members revealed the average calving interval is now 14.5 months, the longest since Virginia DHI started reported summaries. It is not efficient or profitable for the majority of farms to have a 14.5 month calving interval. The major inputs that determine the costs of extended calving intervals are the level of milk production, milk price, culling rate, and cost of replacements. We are presently experiencing record highs for milk production, milk price, and cost of replacements. Therefore, the cost of extended calving intervals is more expensive now than ever before. Detection of cows in heat is half the pregnancy rate equation. Realize it is difficult to observe cows in heat because cows come into heat equally during all hours of the day, are not very active, and do not stay in heat very long. The equal distribution of the onset of estrus during the day combined with an average duration of estrus of 8 hours dictate heat detection observations should occur 3 to 4 times daily, approximately 6 to 8 hours apart. To achieve accurate and efficient heat detection requires extra effort and organization. Most farms detection of cows in heat has failed because only 40% of all cows that should be detected are actually observed and inseminated. Cycling cows require good nutrition, excellent cow comfort, the best hoof health possible, and attention to details. Methods of synchronizing estrus were originally devised to decrease the time spent detecting estrus; however, systematic breeding programs especially Ovsynch and Pre-Synch are now being used for convenience while increasing pregnancy rates and decreasing days to first service. Systematic breeding programs provide an organized approach for administering AI at first service and achieve higher pregnancy rates because more cows have a chance to become pregnant. Ovsynch consists of a GnRH injection at a random stage of the estrous cycle, followed by PGF2 7 days later, a second GnRH injection 36 to 48 hours after PGF2, and timed AI 12 to 16 hours after the last GnRH injection. Routinely, pregnancy rates of 25 to 35 percent are achieved in dairy cows inseminated at first service, using the Ovsynch protocol. However, it is possible to manipulate the estrous cycle of cows such that they are in the ideal stage of the estrous cycle when the Ovsynch program is initiated. Thus, the name Pre-synch which applies two injections of PGF2 14 days apart with the second PGF2 injection 12 to 14 days before the initiation of Ovsynch. The Pre-synch protocol groups a high percentage of the cows into Days 5 to 12 of their estrous cycles when the first GnRH injection of Ovsynch is given. Modification of the Ovsynch protocol to Pre-synch is shown below with suggested days in milk (DIM) at each hormone injection.

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