SELECTIONS - Summer 2002
So You Synchronized Estrus -
Now What?
By Mel DeJarnette, reproduction specialist
Systematic breeding programs such as Ovsynch and target
breeding have allowed many dairy producers to reduce days
to first service and improve pregnancy rates to these early
inseminations. This usually translates into improved overall
reproductive performance in other traits such as average days
open and calving interval. However, some herds have found that
despite these improvements, other barometers of reproductive
performance do not appear to have changed much. This is likely
a result of assuming that these breeding programs eliminate
the need for estrus detection.
Strategic and systematic use of these programs ensures that 100
percent of the herd receives the first A.I. service within a
reasonable amount of time after calving, and usually results in
a 30 percent to 35 percent pregnancy rate at first A.I. But,
they still leave us with 65 percent to 70 percent of the herd
open. So what happens to these cows? In herds where the manager
believes systematic breeding reduces the need or importance for
heat detection, the repeats are less likely to be detected than
they were before adoption of the breeding program.
Therefore, the benefits of timely first service and pregnancy
often are offset by later detection, insemination and conception
in repeat cows. Many producers are beginning to recognize the
dollars being left on the table are there for the taking by
those who adopt systematic "rebreeding programs."
Once a group of cows is synchronized, it tends to stay somewhat
synchronized for the next one or two estrous cycles. By taking
advantage of a heat expectancy list and estrous-detection aids
such as chalk or KAMARs®, a good herd manager should be able to
catch a high percentage of these cows when they repeat 18 to 24
days later. For herds on a prostaglandin-based breeding program,
scheduling groups of cows at three-week intervals will result in
a "synchronized" group of cows displaying estrus simultaneously
with the repeats from the previous injection. This will further
facilitate estrous detection in these repeat animals. If the first
service was to Ovsynch, it would be a good idea to also watch for
repeats 10 to 14 days after the previous A.I. service. This is
because any anestrous cows that were induced to cycle in response
to the GnRH injections of Ovsynch often will display a shorter
interval to estrus if they fail to conceive.
Ongoing research soon may provide techniques we can recommend to
"resynchronize" repeats and further improve estrous-detection rates.
In the meantime, with good heat detection you should have a goal of
catching 50 percent or more of the open cows when they return to
estrus. If 40 percent to 50 percent conceive to these repeat
inseminations, an additional 13 percent to 16 percent will be
added to the pregnancy rate. This brings the tally for the first
25 days after the voluntary waiting period to approximately 40 percent
to 50 percent of the herd.
But, that still leaves at least half of the herd open. Early detection
of these open cows and timely reinsemination is essential to keep
them from becoming costly liabilities.
With conventional reproductive management programs, detection and
reinsemination of open cows traditionally has been accomplished by
rectal palpation of pregnancy at 30 to 40 days after A.I., and
injecting open cows with prostaglandin. This technique is a least-cost
approach that works if the heat-detection program is intense enough
to catch cows as they respond to the prostaglandin. Unfortunately,
despite their best efforts, many producers find that a high percentage
of these cows continue to slip through the cracks of the heat-detection
program using the prostaglandin-only approach to rebreeding.
An alternative to the prostaglandin-only approach is to immediately
start the Ovsynch program on open cows after a veterinary check. This
ensures 100 percent of the open cows will be reinseminated 10 days later.
If you like the idea of using Ovsynch on open cows, but don't like the
idea of waiting 10 days to reinseminate (at a $3 per day cost for days
open), you may want to try the following approach. Restart the Ovsynch
program with a GnRH injection at 25 to 27 days after A.I. service in
all cows that did not return to estrus. Check all cows for pregnancy
six or seven days later (day 31 to 34 after A.I.). Pregnant cows receive
no further treatment, while open cows continue with the Ovsynch program
(prostaglandin seven days after the GnRH followed by another GnRH 48 hours
after the prostaglandin, and fixed-time A.I. eight to 18 hours after
the second GnRH).
Although the day-25-to-27 GnRH injection is "wasted" in pregnant cows,
these costs easily can be offset by the seven-day reduction in the interval
to repeat insemination of open cows. In herds that use ultrasound to
diagnose pregnancy as early as 23 to 25 days after A.I., further efficiencies
can be gained through more accurate pregnancy diagnosis and deferred GnRH
cost by only starting the open cows on Ovsynch again.
Regardless of the resynchronization option you choose, it is extremely
important to keep accurate records to ensure that pregnant cows are not
inadvertently injected with prostaglandin and/or reinseminated, as either
will result in an abortion.
Although synchronization programs can reduce our dependency on heat detection
for breeding and rebreeding, they do not eliminate the need for heat detection.
Take advantage of the synchrony created by a previous synchronization by
intensely focusing on detection of repeats 18 to 24 days later. Each animal
detected will be re-inseminated at least 10 to 14 days earlier than would
be possible with any pregnancy-check-based resynchronization program and
no additional hormone expense will be required. In addition, despite our
best efforts to teach them, many cows do not read the book. Natural heats
and repeats occur daily even in the most intensely synchronized herds.
Take advantage of these "freebies" by providing at least moderate levels
of estrous detection on a daily basis.
The profitability of any cattle-breeding enterprise hinges on timely
insemination and conception. Although systematic breeding programs greatly
enhanced the efficiency with which we can deliver the first A.I. service
after calving, tremendous returns on investment await those who develop
and implement systematic protocols to detect and reinseminate those cows
that fail to conceive at the first service.
Synchronization Schedules for Commonly Used Programs
reprinted with permission from Dairy Herd Management
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