Cattle Today

Cattle Today

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by: Stephen B. Blezinger
Ph.D., PAS

Part 2

In the last issue you will recall that we began a discussion of heat synchronization in cattle. Given the response I've received, one would be lead to believe this is a matter of considerable interest to many breeders, commercial and purebred alike. In this issue, we'll continue this discussion, outlining more of the programs that are available for use by the cattleman. Each of these programs is designed to concentrate the breeding and subsequent calving.

A Reminder

One very important point to remember is this: synchronization of the estrus cycle can only take place in females that are already cycling. Many producers have fallen into the thought pattern that the synchronization process will bring non-cycling cows into heat. This is not the case. These cattle must ALREADY be cycling before a synchronization program can be effectively implemented. In general synchronization works by manipulating the hormones that affect reproductive activity in various stages of the process. Different compounds affect different stages but with the same outcome -- suppression of heat and subsequent breeding activity in a group of females until a specified time.

Programs and Products

In the last issue we looked at some of the progestogen compounds, the ones which mimic the action of progesterone such as Synchro-mate B or Melegesterol Acetate (MGA). In this issue we'll examine several compounds which accomplish this task but in a somewhat different manner. You'll recall from the background information in the previous issue that another manner of synchronizing heat involves Prostaglandin F2a (PGF2a). Remember that in non-pregnant cows, the uterus releases a hormone called PGF2a late in the cycle. This hormone breaks down the corpus luteum which causes the progesterone level to drop and the cow again comes into heat. This removes the inhibitory effect of progesterone on Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) production. Let's take a look at some of these programs.

C. Products based on Prostaglandin F2a

Products available for this type of program include the following:

      Lutalyse (Dinoprost Tromethamine) - an analog of PGF2a

      Estrumate (Cloprostenol) - synthetic analog of PGF2a

      Bovilene (Fenprostalene) - synthetic analog of PGF2a

      Prostamate (Dinoprost Tromethamine) - an analog of PGF2a

With each of these products remember that the compound causes luteolysis (breakdown of the corpus luteum) which then causes progesterone production to drop. This then reduces the effect of progesterone.

The Programs

As with all synchronizing programs, advanced planning is required.

I. Option 1

a) begin this type of program by injecting cycling females with PGF2a at 11 day intervals.

b) breed in one of two ways:

      1) inseminate all cows between 72 and 80 hours after the second injection without regard for estrus.

      2) inseminate each cow at 12 hours after detected estrus.

II. Option 2

a) inject PGF2a and breed cows detected in estrus during the subsequent 5 day period.

b) cows not detected during this period will receive a second PGF2a injection 11 days after the first and should be bred at a fixed time or on detection as discussed previously.

III.      Option 3

      a) Detect estrus for 5 days and breed. On the 5th day inject with PGF2a in cows which have not been observed in estrus.

b) continue breeding for 5 more days based on detection.

Advantages of this program are that one injection will effectively synchronize any cow with an active corpus luteum. Additionally, this method requires a comparatively small amount of time and labor to administer. The disadvantages, however, are significant. Use of this program will abort females which are less than 150 days pregnant. Injections must be given twice (11 to 12 days apart) to synchronize all cycling animals since one injection will affect only those individuals having an active CL at day 6 or greater. Finally it can cause abortions in pregnant women and likely cause bronchiospasms in asthmatics. Obviously the downsides of this program must be carefully considered

D. Combination of Progestogen and PGF2a

Yet another option includes a combination of both types of compounds. This requires even more planning since it requires about 30 days to implement.

The Program

The progestogen used can be of any of the types discussed earlier as can the PGF2a. As with the programs discussed before, several options exist for these methods as well.

I. Option 1

a)      administer the progestogen via feed or implant for 7 to 9 days.

b)      on the day prior to progestogen withdrawal, inject with PGF2a

c)      breed for 12 hours after the onset of estrus or at a fixed time of 72 to 80 hours after administration of PGF2a.

II. Option 2

a) administer the progestogen via feed or implant for 11 to 14 days.

b) 17 days after progestogen has been withdrawn, inject with PGF2a. This is a total of 28 to 31 days after program initiation

c) breed for 12 hours after the onset of estrus or at a fixed time of 72 to 80 hours after administration of PGF2a.

Obviously a potential downside, as discussed before, is the additional planning needed to implement this program. The effectiveness is considered good, however, and should be considered a distinct advantage.

E. Gonadotropin Releasing Hormone (GnRH) plus PGF2a

The program works on a concept slightly different than what has already been discussed. Gonadotropin Releasing Hormone (GnRH) is a compound which causes the ovulation of the dominant follicle on the ovary.

The Program

This program uses a product called Ov-Synch which synchronizes ovulation and uses a three injection scheme.

a) On day 1, a GnRH injection is given to stimulate ovulation

b) on day 5 to 7 detect estrus and breed.

c) 7 days later an injection of PGF2a is given to regress the CL in those cows not bred.

d) a second GnRH injection is given 2 days later to force a new dominant follicle to ovulate after 26 to 30 hours.

e) breed by A. I. 20 to 24 hours after the last GnRh injection is given or detect heat and breed.

This is also a good program but requires added planning as well as extra time and labor for the additional injection need for some cows.

Program and Product Evaluation

It's obvious that a lot of options exist in selecting a synchronization program and no one program works the best for all producers. To evaluate a given program the following factors must be considered.

      Product cost

      Time of administration. Heat detection and breeding will have to be conducive to your schedule and labor resources.

      Mechanism and effectiveness of the product

      Safety in use of the product

      Timed A. I. or estrus detection

Ultimately it comes down to how many cows you can get bred in the time frame you desire. Synchronization is an excellent tool to improve performance and the overall value of a herd AND the subsequent calf-crop. Like anything else it takes time and planning.

Finally, we want to wish you all the most prosperous and blessed New Year ever. Thanks very much for the attention you have given these articles during the past year. I sincerely appreciate the many kind notes and calls I've received and the encouragement. See you in 2001!

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, Texas. he can be reached at P. O. Box 653 Sulphur Springs, TX 75483, by phone at (903) 885-7992 or by e-mail at


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