Use of Presynchronization Protocol and bST with Ovsynch to Improve Reproduction

Dr. Allen Young
USU Extension Dairy Specialist

    At the recent Western Dairy Management Conference in Las Vegas, Dr. William Thatcher from the University of Florida gave an interesting talk on Factors Influencing Reproductive Efficiency. I want to focus on one set of experiments that he reported because they illustrate a couple of points regarding reproduction that may be of interest to you.

    I suspect that most of you have heard about the Ovsynch protocol. It was originally developed at the University of Wisconsin and has been modified and tested by many other researchers. In summary, the protocol begins with a shot of GnRH (e.g., Cystorelin) at some predetermined point in time after calving. This is to cause ovulation of any existing follicle on the ovary. Seven (7) days later, a shot of PGF2% (e.g., Lutalyse) is given to ‘kill’ the resulting corpus luteum (C.L.) on the ovary. Two (2) days after that, another shot of GnRH is given, and cows are inseminated approximately 16 hours later. The value of this protocol is that NO heat detection is required because ovulations should be synchronized. The downside is that this protocol works best if the cow is between day 5 and 10 of her estrous cycle at the first GnRH injection. Dr. Thatcher added a presynchronization protocol to the Ovsynch protocol in an effort to get as many cows as possible into the day 5 to 10 window. He did this by injecting cows that were between days 34 - 40 after calving (average 37) with PGF2%, then gave another PGF2% injection 14 days later. The Ovsynch protocol was begun 12 days after that (if you are keeping track, Ovsynch would begin on day 63 after calving and insemination on day 73). Cows were checked at 32 days after insemination for pregnancy, and open cows began the Ovsynch protocol again. Pregnant cows were checked 42 days after this to reconfirm pregnancy.

    Pregnancy rates from this part of the experiment were 41.7% for those cows that were cycling and 22.4% for those animals not cycling. Overall, 23.4% of the cows were not cycling by day 63 after calving. Repeating the Ovsynch protocol induced cyclicity in 74.5% of the cows that were NOT cycling, with 28.4% of these cows becoming pregnant. Presynchronization of cows increased the pregnancy rate from 25.3% to 42.6%. The take-home message is that presynchronization can improve pregnancy rates and that the Ovsynch protocol can induce anestrous cows to cycle.

    An additional twist to the experiment was to give bST on either day 63 or 73 (i.e., at the start of Ovsynch or the day of insemination). Administering bST increased first-service pregnancy rates by approximately 23% (34% to 57%) for presynchronized compared with nonsynchronized cows (Table 1). This supports earlier research by Dr. Thatcher and other researchers that bST given with an Ovsynch protocol increases pregnancy rates. Many producers are concerned about the possible negative impact of bST on reproduction; however, most research supports Thatcher’s findings that this product should not impair, and may even enhance, reproduction.

    In summary, if you are having a hard time catching cows in heat, consider using an Ovsynch protocol. Thatcher’s data suggest that there is an added benefit from using some type of presynchronization program, and that bST used at the beginning of an Ovsynch protocol or at insemination during the same protocol enhances reproductive performance and could be used to improve reproduction on your farm.

Table 1. First service pregnancy rates for cycling cows following Ovsynch protocol.
First Service Pregnancy Rate (%)
No Presynchronization control25.3
No Presynch + bST - d 6334.2
No Presynch + bST - d 7333.7
Presynchronization control42.6
Presynch + bST - d 6358.1
Presynch + bST - d 7356.1