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.