SELECTIONS - Summer 2002
What's New in Estrus Synchronization?
By Mel DeJarnette, reproduction specialist
If you’ve ever felt overwhelmed by the number of different
protocols available for synchronizing estrus, I'm afraid I
must report that it's not likely to get any less confusing
in the near future.
The annual meeting of the American Animal Science and Dairy
Science associations was held the third week of July in Quebec
City in conjunction with the Canadian Animal Science Association.
At this meeting there were about 60 abstracts presented that
discussed estrus synchronization in cattle. While this added
information will not help you keep your sanity, it hopefully
is adding information that will help us get more cows pregnant.
Heatsynch versus Ovsynch
There were a baker's dozen abstracts related to the use of
estradiol cypionate (ECP) in protocols for estrus synchronization.
ECP is a commercially available form of the natural hormone, estrogen.
Estrogen is the hormone that causes cows to show the many signs of
heat when they come into estrus, and it creates a surge-type release
of gonadotropin-releasing hormone (GnRH) from the brain. GnRH, in turn,
causes the release of luteinizing hormone (LH), which results in ovulation
of the mature follicle. GnRH is the hormone that is used to induce ovulation
in the popular timed-A.I. protocol known as Ovsynch.
Heatsynch is a newly developed synchronization protocol that uses the
less-expensive hormone ECP in place of the second GnRH injection of
the Ovsynch protocol. However, because of differences in how these
hormones work, there also are several important differences in protocol
implementation.
To induce ovulation in cattle, we must first induce a surge of LH. The
difference between using GnRH or ECP to induce an LH surge is equivalent
to the difference between flying from Los Angeles to New York on a direct
flight versus a connecting flight. No matter how good your connection,
direct flights always will get you there more quickly. GnRH has a direct
and almost immediate effect on the release of LH, while ECP has a delayed
effect. A recent study6 found that cows injected with GnRH have an LH
surge within an hour or so, while the LH surge of ECP-treated cows was
not detected for about 41 hours. This difference in time to LH surge
means the hormone injection intervals must also be altered when substituting
ECP for GnRH. Both Ovsynch and Heatsynch call for a GnRH injection followed
seven days later with an injection of PGF. Heatsynch then prescribes a
one-milligram injection of ECP 24 hours later, while Ovsynch-treated cows
receive GnRH 48 hours later (Figure 1).
Because of the delayed interval to the LH surge, the recommended interval
to fixed-time A.I. is 72 hours after PGF (48 hours after ECP) for Heatsynch,
compared with 56 to 64 hours after PGF (eight to 16 hours after GnRH) for Ovsynch.
The biggest difference that producers immediately will notice between Heatsynch
and Ovsynch is the percentage of cows that will show visual signs of estrus.
ECP, as all estrogens, stimulates estrus expression following injection.
Heatsynch cows detected in estrus should be bred according to the "a.m./p.m.
rule" or at 72 hours after PGF, whichever comes first. In contrast, the second
GnRH injection of Ovsynch induces the LH surge and ovulation almost immediately,
shutting down estrogen production from the growing follicle and thus, very few
cows will show heat even though they are ovulating.
The increased estrous activity from Heatsynch certainly makes producers and
technicians feel better about breeding cows, but that does not necessarily
mean it's a better synchronization protocol. In one study6, even though 40
percent of Heatsynch cows were detected in estrus compared to only 8 percent
for Ovsynch, only 59 percent of Heatsynch cows ovulated following PGF injection
compared to 83 percent for Ovsynch. Additionally, some producers have found
this increased estrous activity of Heatsynch is not necessarily a positive
if footing surfaces are less than optimal. This is particularly important
to remember during the icy winter months.
Although cows that show heat almost always will have better conception rates
than those that don't, all controlled studies directly comparing Heatsynch
and Ovsynch basically have achieved identical overall pregnancy rates. The
major advantages of Heatsynch compared to Ovsynch are reduced hormone costs,
more efficient use of expensive semen in higher conception-rate cows that
are allowed to express estrus, and somewhat easier scheduling and implementation,
since all injections and A.I. are at 24-hour intervals.
Even though you'll be a few hours later when using connecting flights, they
will get you to your final destination as well as direct flights, provided
all goes well. However, you don't have to fly very often before you realize
that connecting flights present an increased opportunity for "things to
happen." When things happen (weather delays, missed connections, lost baggage),
you often find yourself wishing you had taken the more expensive direct flight.
The same might be said for Heatsynch and Ovsynch. Perhaps because of the more
direct effects of GnRH on LH secretion, researchers in Florida1 found that
Ovsynch is more effective in cystic cows, while Heatsynch appeared more
effective in cows that were in heat a few days before start of treatment.
The original Heatsynch publication5 observed interactions between synchronization
treatment and both parity (Figure 2) and cycling status (Figure 3).
The bottom line of the Heatsynch/Ovsynch debate is: "they both work." So do
several other systematic breeding programs. We need to stop "splitting hairs"
about which one "works the best." The important thing is to pick a program
that fits your management, and your management team's ability to implement
and follow protocol. If you do this, you will be happy with the results of
most any system you choose. If management fails to successfully implement,
you'll likewise be dissatisfied with the results of any protocol selected.
With the success of the protocols available today, there is simply no
excuse for excessive days open at first A.I. Herds with lots of cows
reaching 100 days or more in milk before receiving their first A.I. need
to quit talking about how expensive synchronization programs are and
start thinking about how expensive it is to not have a synchronization program.
The EAZI-BREED™ CIDR®
The EAZI-BREED CIDR Cattle Insert, or CIDR as it's most commonly called, is
the newest synchronization product available in the U.S. market. Developed
and used extensively in New Zealand and marketed in the United States by
Pharmacia Animal Health, the CIDR is a vaginal insert that delivers the
natural hormone progesterone throughout the seven-day implant period. This
progestin stimulation helps to induce cyclicity in anestrous beef cows and
advances puberty in beef heifers.
Used with an injection of LUTALYSE® on day six after insertion and implant
removal on day seven, research has shown the CIDR to be an effective means
of synchronizing estrus in virgin beef and dairy heifers, and in postpartum
beef cows (Figure 4). The CIDR is not approved for use in lactating dairy cattle.
Animals may either be bred to detected estrus for three or four days after
CIDR removal or fixed-time inseminated at 48 to 54 hours after implant
removal. Although labeled for a day six LUTALYSE injection, practical
implementation in most other countries usually involves moving the LUTALYSE
to day seven, which eliminates one animal handling with no indications
of reduced efficacy.
While the CIDR is certainly an interesting and effective new tool for
synchronizing estrus in cattle, it appears from the rumor mill that a
problem exists in terms of realistic expectations. Although the rumors
of 90 percent estrous-response rates are true, these are exceptions and
not the averages. One of the studies3 that was used to demonstrate efficacy
for the U.S. Food and Drug Administration (FDA) approval is presented in
Table 1. Although pregnancy rates in excess of 50 percent are certainly
possible, the data suggests that even when working with the improbable
case of 100 percent cyclicity, pregnancy rates in excess of 50 percent
are not guaranteed. However, no matter how you measure it, the CIDR works
better than LUTALYSE alone.
Numerous other studies have evaluated the use of the CIDR within the
Ovsynch or Cosynch protocols (e.g., Insert CIDR and inject GnRH; remove
CIDR and inject LUTALYSE seven days later). Most studies, including the
one outlined in Figure 5, suggest improved reproductive performance in
beef cows using this approach.
What About Reusing CIDRs?
There are lots of rumors floating around about reusing CIDRs. However, there
are a few important risks to consider. Aside from legal issues, one of the
major reasons one might select the CIDR over other synchronization protocols
is the ability to induce cyclicity in anestrous cows and prepubertal heifers.
To my knowledge, there are no studies available to document the efficacy of
a used CIDR to induce cyclicity. In fact, the U.S. version was designed to
have minimal residual progesterone upon removal, which would not suggest
them to be effective for this use.
Last, but certainly not least, regardless of how well you try to clean them,
the sanitation of a used CIDR is compromised and increases the risk of
disease transmission within the herd. Just like putting a fast sports car in
the hands of a teenager, a used CIDR is a wreck looking for a place to happen.
Is it really worth the risk?
Presynch
In the last issue of Selections, we reprinted a figure from a Dairy Herd
Management article that described various protocols for estrus synchronization.
The description of Presynch in that table generated enough confusion and
telephone calls that I'd like to clarify the information.
Presynch, as the name would imply, refers to what happens before synchronization.
Specifically, Presynch is simply two PGF injections given at 14-day intervals
to set up cows so they will be the right stage of the estrous cycle for optimum
response when the synchronization protocol is initiated some number of days
later. The actual synchronization protocol used could be any of these: Ovsynch,
Heatsynch, Cosynch or Select Synch.
The original Presynch research suggested the synchronization protocol should
be initiated 12 days after the second PGF injection. However, a recent study4
confirmed that a 14-day interval between Presynch and synchronization
(which is easier to schedule) will also improve pregnancy rates to
fixed-time A.I.
Final Thoughts
Although it certainly gets confusing these days trying to keep up with
research related to synchronizing estrus in cattle, it’s no doubt these
techniques are becoming extremely valuable tools to help beef and dairy
producers generate pregnancies in a more timely fashion. How do you know
if you need a synchronization program for your herd? Simple. Do you have
cows reaching 100 days or more in milk before their first breeding? If yes,
you should be using some form of synchronization. The more cows you have
reaching this threshhold, the more intensive of a synchronization program
you should consider adapting. If you need help deciding which system is
most adaptable to your herd management, contact your veterinarian or your
local Select Sires Reproductive Solutions™ specialist.
Literature Cited
- Bartolome, J.A., F.T. Silvestre, A.C.M. Arteche, S. Kamimura,
L.F. Archbald and W.W. Thatcher. 2002. The use of Ovsynch and
Heatsynch for resynchronization of cows open at pregnancy diagnosis
by ultrasonography. J. Dairy Sci. 85 (Suppl. 1):99 (abstr.)
- Lamb, G.C., J.S. Stevenson, D.J. Kesler, H.A. Garverick, D.R. Brown
and B.E. Salfen. 2001. Inclusion of an intravaginal progesterone
insert plus GnRH and prostaglandin F2a for ovulation control in
postpartum suckled beef cows. J. Anim. Sci. 79:2253-2259.
- Lucy, M.C., H.J. Billings, W.R. Butler, L.R. Ehnis, M.J. Fields,
D.J. Kesler, J.E. Kinder, R.C. Mattos, R.E. Short, W.W. Thatcher,
R.P. Wettemann, J.V. Yelich and H.D. Haf. 2001. Efficacy of an
intravaginal progesterone insert and an injection of PGF for
synchronizing estrus and shortening the interval to pregnancy
in postpartum beef cows, peripubertal beef heifers and dairy
heifers. J. Anim. Sci. 79:982-995.
- Navanukraw, C., L.P. Reynolds, A.T. Grazul-Bilska, D.A. Redmer
and P.M. Fricke. 2002. Effect of presynchronization on conception
rate to a timed artificial insemination protocol in lactating dairy
cows. J. Dairy Sci. 85 (Suppl. 1):263 (abstr.).
- Pancarci, S.M., E.R. Jordan, C.A. Risco, M.J. Schouten, F.L. Lopes,
F. Moreira and W.W. Thatcher. 2002. Use of estradiol cypionate in a
presynchronized timed artificial insemination program for lactating
dairy cattle. J. Dairy Sci. 85:122-131.
- Stevenson, J.S., S.M. Tiffany and M.C. Lucy. 2002. Incidence and
timing of estrus, LH surge, and ovulation in cows treated with the
Ovsynch protocol with estradiol cypionate (ECP) Substituting for
GnRH. J. Dairy Sci. 85 (Suppl. 1):99 (abstr.).
®CIDR is a registered trademark of InterAg, Hamilton, New Zealand
®LUTALYSE is a registered trademark of Pharmacia Corporation
™EAZI-BREED is a trademark of InterAg, Hamilton, New Zealand
™Reproductive Solutions is a trademark of Select Sires Inc.
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