Synchronizing Estrus In Beef Cattle

Synchronizing Estrus In Beef Cattle

  Dr. Rick Rasby, Beef Specialist, University of Nebraska - Lincoln
  Gene Deutscher, Emeritus Professor, University of Nebraska


Synchronization of estrus (heat) involves manipulating the estrous cycle of beef females so they can be bred at approximately the same time. There are several protocols available for synchronizing estrus among beef females. Traditional protocols are designed to mimic or control the corpus luteum on the ovary. New protocols have been designed to control ovulation and/or the follicular waves that occur on the ovary during the 21-day estrous cycle.

Products Used to Synchronize Estrus in Beef Cattle

There are three primary groups of products used to synchronize estrus or ovulation in beef cattle: prostaglandins, progestins, and gonadotropins. Prostaglandin products have the trade names of Lutalyse, Estrumate, and IN-SYNCH and each contain prostaglandin F2a (PGF2a) or an analogue of PGF2a. The progestin products include the vaginal implant CIDR® and Melengestrol Acetate (MGA), that is consumed orally. The GnRH products are Cystrorelin, Factrel, and Fertagyl.

Table 1. Products to synchronize estrus in beef cattle
Product Dosea Approved Label Use
    Lutalyse ®
    Estrumate ®
    IN-SYNC ®
5 mL, im
2 mL, im
5 mL, im
beef heifers and cows
beef heifers and cows
beef heifers and cows
    MGA ® c
Vaginal insertb
0.5 mg/hd/day, oral
beef heifers and cows
beef heifers (estrus suppression only c)
    Cystrolrelin ® d
    Factrel ® d
    Fertagyl ® d
2 mL, im or iv
2 mL, im
2 mL, im or iv
bovine females
dairy females
bovine females

a Strict adherence to label warnings and precautions should be observed. Follow Beef Quality Assurance (BQA) injection site procedures.
b CIDR® Contains 1.38 grams of progesterone in silicone, molded over a nylon spine.
c MGA is approved for suppressing estrus in feedlot heifers to improve performance in animals intended for slaughter. It does not carry FDA approval as a product to synchronize estrus.
d Products used to treat cystic follicles in beef and dairy cattle.

Estrous Synchronization Protocols

Prostaglandin Protocols to Synchronize Estrus

There are four prostaglandin protocols being used to synchronize estrus in cattle. Two of these programs require two injections of prostaglandin and two require just one injection.

Figure 1 graphic
Figure 1. One injection prostaglandin protocol with 5 days of AI.
One Injection of Prostaglandin With 5 Days of Breeding Protocol

Inject all females with prostaglandin on Day 0 and check for estrus and breed 12 hours after standing estrus (see Figure 1). With a single injection of prostaglandin about 75% of the cycling females would be expected to display estrus during the next 2 to 5 days. Anestrous cows, will not respond to this prostaglandin protocol because they do not have a CL present on the ovary.

One Injection of Prostaglandin With 10 Days of Breeding Protocol
Figure 2 graphic
Figure 2. One injection progstaglandin protocol with 10 days of AI.

Check for estrus and breed all females in standing estrus for the first five days of the breeding season (see Figure 2). Inject all females with prostaglandin not previously bred at the end of day 5 and breed these females 12 hours after standing heat. By breeding for 5 days, none of the cows that receive the prostaglandin injection will be between day 1 to 5 of their estrous cycle. Cows that are cycling should display estrus within 2 to 5 days after the prostaglandin injection. This protocol can result in greater than 90% of cyclic females being inseminated during the first 10 days of the breeding season.

Two Injections with Prostaglandin Protocol With 10 Days of Breeding
Figure 3
Figure 3. Two injection progstaglandin protocol with 10 days of AI.

The two injection programs for synchronization with prostaglandin allow for females to be inseminated after each prostaglandin injection or for insemination only after the second injection. In this protocol, an injection of prostaglandin is given to all cows (see Figure 3). After one injection, about 75% of the cycling females should be in heat during the next 5 days. Females that are detected in estrus should be inseminated 12 hours later. The females that are not detected in heat and bred after the first injection should receive a second prostaglandin injection 11 or 14 days later and be bred 12 hours after they display standing estrus. When breeding females after each injection, be sure not to inject prostaglandin into females that were inseminated after the first injection.

Two Injections with Prostaglandin Protocol With 5 Days of Breeding
Figure 4
Figure 4. Two injection progstaglandin protocol with AI after the second injection.

Traditionally, the injections of prostaglandin are administered 11 days apart with breeding after the second injection (see Figure 4). However, recent data suggests that administering the second injection 14 days after the first injection has resulted in more females exhibiting estrus. The two injection protocol should theoretically synchronize estrus in cyclic females within 2 to 5 days after the second injection. Synchronization responses of 70 to 80% of females within a herd are common with this protocol, but can be highly variable depending on the number of anestrous females in the herd. Timed insemination with this protocol is not recommended.

Key Points
  • Nutrition program so that mature cows calve in a Body Condition Score of 5 and first -calf-heifers in Body Condition Score of 6.
  • Nutrition program for replacement heifer such that they reach puberty and begin estrous cycles at least 3 weeks before the start of the breeding season.
  • Females must be exhibiting estrous cycles.
  • Cows at least 40 to 50 days post-calving.
  • Good facilities to restrain and handle cattle.
  • Trained people in detecting estrus (heat).
  • Timed breeding is not recommended.
Using MGA and Prostaglandin Protocol to Synchronize Estrus
Figure 5
Figure 5. MGA - Progstaglandin synchronization protocol.

A low cost system for estrous synchronization uses Melengestrol Acetate (MGA) and prostaglandin (see Figure 5). MGA is a "progesterone-like" feed additive that suppresses estrus in feedlot heifers and is not approved by FDA to synchronize estrus. However, it is approved to suppress estrus in heifers in a feedlot and because heifers are usually confined in a dry-lot during development and breeding, especially if artificial insemination is used, MGA can be used in this protocol. MGA is fed at .5 mg/head/day for 14 days. Females will exhibit estrus two to five days after withdrawal of the MGA. The estrus that occurs immediately after MGA feeding subfertile and females should not be bred on this estrus. A single injection of prostaglandin is administered 17 (or 19 days) days after the MGA has been removed from the feeding program. Most females will exhibit estrus 48 to 72 hours after the prostaglandin injection. Inseminate females 12 hours after standing estrus.

This protocol is capable of inducing estrous cycles in some females that are not yet cycling. Timed mating all females or those that have not yet displayed heat at 72 hours (heifers) or 80 hours (cows) after the prostaglandin injection results in additional pregnancies.

Key Points
  • Protocol must be initiated 31 days before the start of the breeding season.
  • Pregnancy rates are more variable when used on mature, lactating cows.
  • Females in good body condition.
  • Females fed a ration that MGA can be easily incorporated into.
  • Each female consumes .5 mg of MGA daily.
  • Adequate bunk space.
  • Females can be time inseminated but conception rates are variable.
  • MGA is approved by FDA to suppress estrus in feed-lot heifers.
Synchronization of Estrus Using the Vaginal Insert CIDR®
Figure 6
Figure 6. Synchronization of Estrus using the vaginal insert CIDR®

Estrous synchronization using the vaginal insert CIDR® consists of placing the insert in the vagina on day 0, giving an injection of prostaglandin on day 6, and removing the vaginal insert on day 7 (see Figure 6). Detect heat from days 8 to 11 and inseminate all females that exhibit estrus. To assure satisfactory synchronization of estrus, an injection of prostaglandin must be given to all females one day before the removal of the vaginal insert. Removal of the insert on day 7 results in a drop in circulating plasma progesterone, triggering estrus within three to four days. The progestin in the vaginal insert can induce estrous cycles in anestrous cows and advance puberty in heifers. The majority of the females that respond to this protocol will exhibit estrus between 25 and 72 hours after the prostaglandin injection.

Key Points
  • The CIDR inserts are labeled for one-time use only.
  • It is easy to insert and remove the vaginal insert and little animal restraint is needed.
  • Follow instructions on how to dispose of the inserts after use.
  • After placing the vaginal insert in each female, clean applicator.
  • Pregnant women need to be careful and follow label directions when handling prostaglandin products.
  • There is a high retention rate of the insert (90 to 98 percent).
  • There is a tight synchrony of estrus.
  • Induces estrus in some females, therefore potentially more females could become pregnant to artificial insemination.
  • Potentially higher pregnancy rates due to exposure to progesterone prior to breeding.
Select Synch Protocol Using GnRH and Prostaglandin
Figure 7
Figure 7. Select Synch synchronization protocol

A new method for synchronizing estrus in mature beef cows (not for heifers) is to administer a GnRH injection followed one week later by an injection of prostaglandin (see Figure 7). Females are observed for signs of estrus beginning 36 hours before and up to 6 days following the prostaglandin injection. Cows are inseminated 12 hours after standing estrus is observed. Most cows will exhibit estrus by day 4 after prostaglandin injection although some may exhibit estrus up to 6 days after prostaglandin. This protocol has been referred to as the Select Synch protocol.

The estrus following GnRH is fertile and cows can be inseminated. The prostaglandin injection is not necessary in cows that have already exhibited estrus and not yet bred, but will not cause any harm, either. Do not inject prostaglandin in females that have been bred after the GnRH injection. Timed insemination is not recommended when using this protocol.

Key Points
  • Not recommended for heifers.
  • Simple program.
  • Can induce fertile estrous cycles in some cows that are not yet cycling.
  • Cows at least 45 - 55 days postpartum.
  • Cows in good body condition.
  • Use good heat detection technique.
  • Time insemination not recommended.
  • This protocol targeted to follicle development on ovary.
  • Need good animal handling facility.
Co-Synch Protocol Using GnRH and Prostaglandin

There appears to be two possible ways to implement the Co-Synch protocol to synchronize ovulation in beef cows. Whatever the method implemented, they all involve timed insemination on day 9 of the protocol.

Figure 8
Figure 8. Co-Synch synchronization protocol with timed insemination.
Co-Synch with Timed Insemination

A slight variation to the Select Synch protocol involves administering the GnRH injection on day 0, prostaglandin on day 7, and a second GnRH injection on day 9 (48 hours after the prostaglandin injection) at the same time that the cows are time inseminated (see Figure 8). This second GnRH injection initiates a fertile ovulation in cows that have not yet exhibited estrus. The Co-Synch protocol makes heat detection unnecessary and can yield pregnancy rates similar to breeding after detecting estrus.

Co-Synch with 48 Hour Calf Separation and Timed Insemination on Day 9
Figure 9
Figure 9. Co-Synch synchronization protocol with 48-hour calf separation.

Higher pregnancy rates might be obtained by separating the calf from the cow on day 7 at the same time that the prostaglandin injection is given (see Figure 9). An that calves and cows can be separated for 48 hours is needed. About an eight percent increase in pregnancy rate have been obtained.

Key Points
  • Not recommended for heifers.
  • Cows in good body condition.
  • May induce cycling in non-cyclic cows.
  • This protocol targeted to time ovulation in cows.
  • Cows at least 45 - 55 days postpartum.
  • No estrus detection is needed.
  • Need animal handling facility.

Success of Synchronization Program

A successful program requires:

  1. females exhibiting regular estrous cycles;
  2. healthy animals that are free from disease and on a good nutrition program;
  3. a willingness by producers to learn how to use the product(s) and program;
  4. a working facility with a small crowding corral, a holding alley, and chute;
  5. willingness to provide and prepare for extra labor needs;
  6. accurate and thorough detection of estrus; and
  7. a process where females are individually identified and accurate records kept.

When using products for estrous synchronization that need to be injected into the female, use Beef Quality Assurance injection site procedures. When injecting into the neck muscle, consider using a longer needle (1½" inch). It appears that it is more difficult to get to the neck muscles and using the longer needle will aid in depositing the product in the muscle. For these products to act effectively, they must be deposited in the site or sites listed on the label.

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