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Cooperative Extension Service/The University of Georgia College of Agricultural and Environmental Sciences

Estrous SynchronizationFor Beef Cattle

Timothy W. WilsonExtension Animal Scientist — Beef Cattle

As the calving season begins, producers are re-warded for their efforts and hard work.

Everyone enjoys newborn calves, especially whenthey are born as a result of a planned breedingseason the year before. Planning a breeding sea-son can be as simple as defining the time frame abull has to breed a herd, or as intensive as artifi-cial insemination (AI). With AI, producers can useone or more methods of estrous (heat) detection.Some methods of estrous detection require speci-ally designed tools while others require as little as30-45 minutes of visual observation twice a day.Estrous synchronization can minimize the amountof time and labor required to accurately detectestrus.

A quick evaluation of estrous synchronizationprotocols will produce many different methods ofinducing estrus in beef cattle. How do you deter-mine which one is right for your herd? Many fac-tors must be considered when choosing a proto-col. Time, labor, cost and ease of use can play arole in making this decision. Depending on thenumber of estrous cyclic females in the herd, 5percent may be in heat at any given time. As herdsize increases, the potential number of females inheat after synchronization treatment increases.An understanding of how a protocol works is use-ful to ensure that it is performed correctly.

Many reproductive hormones are used inestrous synchronization. Developing a basicunderstanding of several reproductive hormonesis necessary when trying to determine which pro-tocol will work best for your herd.

HormonesProgesterone, prostaglandin (PGF2"), gonado-

tropin releasing hormone (GnRH), follicle stimu-

lating hormone (FSH) and luteinizing hormone(LH) are a few of the hormones involved in theestrous cycle. Depending on the estrous synchro-nization protocol, these hormones can be usedindependently or in combination with oneanother.

Progesterone is a hormone used to maintainpregnancy. Progesterone can be administered inthe natural (progesterone) or synthetic (proges-tin) form. Progesterone and progestins can beused to synchronize estrus in cattle. When thefemale ovulates, the site of ovulation develops astructure known as a corpus hemorrhagicum, whichquickly (within 4 to 7 days) develops into a corpusluteum (CL). The CL is the primary source ofprogesterone in the bloodstream, and as the CLmatures, progesterone concentrations increase.Progesterone concentrations remain elevatedthroughout pregnancy or the estrous cycle untilthe female either calves or determines she is notpregnant. If she is not pregnant within 15 to 18days of a normal estrous cycle, prostaglandin issynthesized and released to regress the corpusluteum. Using the knowledge that progesteroneconcentrations are elevated for most of theestrous cycle and how they are reduced is veryuseful when selecting an estrous synchronizationprotocol.

Prostaglandin (PGF2") is released from theuterus once the female recognizes she is not preg-nant. Prostaglandin causes the CL to regress ordiminish and, once this occurs, progesterone con-centrations decrease rapidly.

Gonadotropin Releasing Hormone (GnRH)is secreted from the hypothalamus and affects theanterior pituitary. As progesterone concentrationsare elevated, GnRH concentrations are decreased.

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The Monday Morning System(Source: Sprott, 1999)

2-Shot Prostaglandin(Source: Sprott, 1999; Stevenson, et al., 2000)

If the CL is regressed, progesterone concentra-tions will decrease in the bloodstream, causingincreased GnRH concentrations. This increase ofGnRH allows for elevated pulsatile secretions offollicle stimulating hormone (FSH) and luteiniz-ing hormone (LH).

The biological site of action for FollicleStimulating Hormone (FSH) is the ovary. Thishormone assists in stimulating follicular wavesand can be manipulated in embryo transfer pro-grams to cause superovulation.

Luteinizing Hormone (LH) is secreted inpulses into the bloodstream and, immediatelybefore ovulation, surges to cause ovulation of thedominant follicle on the ovary.

Estrous Synchronization ProtocolsMany estrous synchronization protocols are

available to producers. Scientists from around theworld perform research to analyze the effective-ness of each protocol. A few of these protocolsthat have been studied include the MondayMorning System (one-shot prostaglandin), two-shot prostaglandin, the MGA/ProstaglandinSystem, the MGA/GnRH/Prostaglandin System,SelectSynch, Co-Synch, Ov-Synch and CIDR/Prostaglandin.

The Monday Morning SystemHeat check and breed for 5 days. Sort cattle

that have not been bred and administer a singleinjection of prostaglandin. Heat check and breedfor 5 additional days. Since females that have beenbred prior to PGF2" injection do not receive thisinjection, fewer doses are used, reducing overalldrug cost. Results of this protocol may vary, andsynchrony may be less than expected.

2-Shot ProstaglandinTwo shots of prostaglandin are injected 11 to

14 days apart, and females are observed for heatand bred for 5 days following the second injection.Research by Stevenson, et al., (2000) has reportedestrous detection rates, conception rates andpregnancy rates of 71.8 percent, 70.6 percent and50.0 percent, respectively, for cyclic cows.

The MGA/PGF2" System and theMGA/GnRH/PGF2" System

Breeding heifers can be difficult and take agreat deal of time. Two protocols that have beenused successfully with heifers use melengestrolacetate (MGA) and prostaglandin.

Melengestrol acetate is an orally active syn-thetic progestin developed to control estrus infeedlot heifers (Lauderdale, et al., 1977). Thisprogestin can be used in estrous synchronizationto mimic progesterone and can stimulate estrus inheifers. In the Southeast, MGA can sometimes bedifficult to find on the market without having totransport it from the Midwest, so having a sourceof MGA before beginning these protocols will beimportant. Since small amounts of MGA are used,be careful when mixing bulk rations to ensureeven distribution throughout the ration.

The MGA/PGF2" system and the MGA/GnRH/PGF2" system are very similar with theexception of a single injection of GnRH. Theaddition of GnRH has been reported to tightensychrony compared to the MGA/PGF2" system(Wood, et al., 2001). Determining which protocolis right for your herd will require several factorsto be evaluated: cost, number of times through thechute, and availability of labor.

The MGA/PGF2" System: Feed MGA for 14days at 0.5 mg/hd/d. A subfertile heat shouldoccur before the shot of prostaglandin is given; donot breed at this time. On day 33, a single injec-

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The MGA/PDF2" System(Source: Wood, et al., 2001)

The MGA/GnRH/PGF2" System(Source: Wood, et al., 2001)

Ov-Synch(Source: Geary and Whittier, 1999)

Select Synch(Source: Geary and Whittier, 1999)

Co-Synch(Source: Geary and Whittier, 1999)

CIDR/Prostaglandin(Source: Pharmacia Animal Health)

tion of prostaglandin is administered intramus-cularly (IM). Check heat and breed from day 33 today 38.

The MGA/GnRH/PGF2" System: FeedMGA for 14 days at 0.5 mg/hd/d. On day 26,inject shot of GnRH IM; follow this 7 days later(day 33) by a shot of prostaglandin IM. Heatcheck and breed from day 33 to day 38.

Select Synch, Co-Synch, Ov-SynchSeveral protocols have been developed using

GnRH and prostaglandin. Each protocol de-scribed is similar in that they involve an injectionof GnRH on day 0 and an injection of prostaglan-din on day 7. Pregnancy rates vary based on heatdetection capabilities. Some estrous synchroniza-tion protocols allow all females to be bred at apredetermined time. This is referred to as “timebreeding.” Time breeding can reduce labor, butpregnancy rates could be reduced compared tofemales bred on standing heats. Time breed pro-tocols have been reported to have pregnancy ratesof 55 percent (Co-Synch) and 52 percent (Ov-Synch) [Geary and Whittier, 1999]. Conceptionrates for these protocols can be increased if a 48-hour calf removal is used after prostaglandininjection (Geary and Whittier, 2001).

Select Synch: Inject GnRH IM on day 0,followed by prostaglandin IM on day 7. Breedcattle that show heat before day 7 and do notinject prostaglandin in those cattle (this will re-duce drug costs). Research by Geary and Whittier

report pregnancy rates of 61 percent for cattlebred based on standing heat.

Co-Synch: GnRH is injected IM on day 0,followed by prostaglandin IM on day 7. GnRH isinjected again on day 9; then time breed.

Ov-Synch: Inject GnRH IM on day 0, followedby prostaglandin IM on day 7. Inject GnRH againat day 9, and time breed on day 10.

CIDRA controlled internal drug releasing device

(CIDR) has recently been approved by the Foodand Drug Administration for use in beef cows andheifers and dairy heifers in the United States.

Current research by Lucy, et al., (2001)reported that 65 percent of beef heifers and 59percent of beef cows were in estrus by day 3 afterCIDR removal. These researchers also reportedthat CIDRs could help stimulate estrous activityin prepubertal heifers.

CIDR/Prostaglandin: Insert the CIDR intra-vaginally on day 0. Give a shot of prostaglandin

on day 6 and remove the CIDR on day 7. Heatcheck and breed from day 7 to day 12.

SummaryDeveloping an understanding of the reproduc-

tive hormones used in estrous synchronizationprotocols can be very useful when trying to deter-mine which protocol will work best for youroperation. Although the estrous synchronizationprotocols mentioned in this publication have beenused in many breeding programs, there may beothers that can also be used successfully.

If you have questions regarding estrous synch-ronization, contact your local county extensionoffice, veterinarian or extension beef specialist forfurther information.

Literature CitedGeary, T.W., J.C. Whittier, D.M. Hallford, and M.D.

MacNeil. 2001. Calf removal improves conceptionrates to the Ovsynch and Co-Synch protocols. J.Anim. Sci. 79:1-4.

Geary, T.W., and J.C. Whittier. 1999. Various proto-cols for synchronization of estrus or ovulation us-ing GnRH and prostaglandin. 1999 Beef ProgramReport. Department of Anim. Sci., Colorado StateUniversity.

Lauderdale, J.W., L.W. Goyings, L.F. Krzeminski, and

R.G. Zimbelman. 1977. Studies of a progestogen(MGA) as related to residues and human consump-tion. J. Tox. and Enviro. Hlth. 3:5-33.

Lucy, M.C., H.J. Billings, W.R. Butler, L.R. Ehnis,M.J. Fields, D.J. Kesler, J.E. Kinder, R.D. Mattos,R.E. Short, W.W. Thatcher, R.P. Wettemann, J.V.Yelich, and H.D. Hafs. 2001. Efficacy of an intra-vaginal progesterone insert and an injection ofPGF2" for synchronizing estrus and shortening theinterval to pregnancy in postpartum beef cows,peripubertal beef heifers, and dairy heifers. J. Anim.Sci. 79:982-995.

Pharmacia Animal Health, EAZI-BREED CIDR,United State Food and Drug Administrationapproved product label. 2002.

Sprott, L.R. 1999. Management and financial consid-erations affecting the decision to synchronizeestrous in beef females. Proc. Am. Soc. Anim. Sci.,1999. At: http://www.asas.org/jas/symposia/proceedings/0025.pdf.

Accessed December, 2002.Stevenson, J.S., K.E. Thompson, W.L. Forbes, G.C.

Lamb, D.M. Grieger, and L.R. Corah. 2000. Syn-chronizing estrus and(or) ovulation in beef cowsafter combinations of GnRH, norgestomet, andprostaglandin F2" with or without timed insemina-tion. J. Anim. Sci. 78: 1747-1758.

Wood, S.L., M.C. Lucy, M.F. Smith, and D.J. Patter-son. 2001. Improved synchrony of estrus and ovu-lation with the addition of GnRH to a melengestrolacetate-prostaglandin F2" synchronization treat-ment in beef heifers. J. Anim. Sci. 79: 2210-2216.

DISCLAIMER: The author of this publication does not advocate any products listed in this publication. Productsmentioned have been described due to specifics of particular estrous synchronization protocols.

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