Cattle Today

Cattle Today

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by: Stephen B. Blezinger

Over the last few weeks we have been discussing the development of a high quality productive cow herd. Over the years we have discussed many aspects pertaining to herd management as related to nutrition and other basic management concepts. In this issue I'd like to venture a little farther from center and look at a management tool that is being used with increased frequency and can significantly increase the value of the calf crop: estrus synchronization. I want to thank, in advance, Dr. Ron Del Vecchio, a beef cattle specialist with Louisiana State University for providing much of this information and for the valuable insight he provided at a recent meeting I attended at which we were both speakers. As a reproduction physiologist, the insights he provided this dumb nutritionist were exceptionally valuable.

Probably the most important task we have on a typical cow/calf operation is getting cows bred. If they're not bred they'll be pretty hard pressed to have a calf. Without a calf to sell, it's going to be awfully difficult for that cow to pay her way. We've discussed many of the concepts pertaining to breeding efficiency and what factors positively and negatively effect how well a cow cycles and breeds. 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. If they are not, the producer is wasting both time and money.

Reproduction Review

Let's take a minute and review how the reproductive cycle in cattle functions. Under normal circumstances, a cow comes into estrus (heat) every 21 days or 3 weeks. When she is in estrus, her standing heat (when she will stand to be bred) lasts 12 to 16 hours on the average. After estrus starts, several events occur. At about 24 to 36 hours after the start of estrus an egg or ova is released from the ovary out of a structure know as a follicle. This is called ovulation. At this point a structure forms on the ovary where the follicle was called the corpus luteum (CL). If the egg is fertilized and the cow becomes pregnant, this CL is maintained until just before calving. Otherwise, the CL regresses and the cycle starts all over again. While present the CL releases the hormone Progesterone which might also be referred to as the hormone of pregnancy. The increased level of progesterone in the blood prevents the animal from returning to estrus by decreasing the production of Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH), both of which are required at higher levels under normal cycling circumstances.

In non-pregnant cows, the uterus releases a hormone called Prostaglandin F2a (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. These two hormones, progesterone and PGF2a are the primary targets of manipulation when we seek to synchronize a group of cattle.

Purpose of Synchronization

The objective of a synchronization program is to breed a high percentage of the females in a given group of heifers or cows in a short period of time, using either artificial insemination (A.I.) or natural service (bulls). Through effective implementation we accomplish the following:

1) Concentration of the breeding season

2) Concentration of the calving season (focuses the workload)

3) More uniform calf crop -- typically improves returns (increases value of calf crop)

4) Facilitates the use of A. I. by concentrating estrus detection requirements.

Although realistically you can never truly eliminate estrus detection, much of the time and effort can be concentrated into a much shorter period of time.

Realistic goals of a well-planned program are to have 50 percent of cycling cows pregnant at the first service/breeding after synchronizing and 80 to 90% pregnant within a 30 day breeding season. Obviously this greatly concentrates the calving and breeding seasons as listed above but the greatest benefit is a tightly grouped calf crop where the majority of the calves are within a few days of age. The one down side of this is the added labor that may be required during the calving period to insure safe deliveries for the herd. This is especially true in heifer groups.

Factors Affecting Optimal Conception

For a synchronization program to work the way it should, several issues must be considered, some of which we have already discussed:

1) Herd Nutrition -- cattle must be in good body condition or on a gaining plane of nutrition. This involves adequate levels of dry matter in general but specifically protein, energy minerals and vitamins.

2) Cattle must be cycling -- as we discussed earlier.

3) Herd Health - prevention and treatment of diseases, control of parasites.

4) Time and labor available for product administration, heat detection and breeding, especially with A. I.

5) Bull to cow ratio -- If natural service is to be used bull to cow ratio has to be considered. Recent studies suggest that one bull can service 25 synchronized females. The bull(s) need to be 2 years or older, experienced and in good condition.

Examples of Synchronization Programs

Let me begin by explaining that the following are by no means a comprehensive list of all the options available to the producer. Additionally, as you go from source to source you will find variations how these programs are implemented. The following descriptions are primarily designed to inform the reader of options available and what is involved.

I. One of the most common programs involves the manipulation of progesterone. The programs have taken several forms over the years:

A.      Synchromate B

Synchromate B is a commonly used product for estrus synchronization. It involves the use of two components: a) a Norgestomet (progestogen) implant and b) an estradiol valerate (estrogen and norgestomet) injection. The initial norgestomet/ progestogen implant has an inhibitory effect on the release of LH and FSH necessary for estrous cycles to continue. In other words it imitates the hormonal conditions necessary for pregnancy. The estradiol valerate causes a breakdown of the corpus luteum by stimulating PGF2a.

The Program

Like all synchronization programs, this requires some advance planning. Initially you need to decide in the future when you want a synchronized heat. Eleven days prior to this date you will need to:

a) insert the Norgestomet implant in the ear.

b) inject intramuscularly with the estradiol valerate/norgestomet solution.

After 9 days:

a) remove the implant

b) breed the animals 12 hours after observing heat

c) OR breed 48 to 72 hours after implant removal without heat detection. This is referred to as “timed A. I.”

d) Introduce clean-up bulls into the herd

The advantages of this pro-gram include 1) administration at any point within the cow's estrus cycle will result in a synchronized estrus. 2) Accidental administration to pregnant cows won't cause abortion. Subsequently, disadvantages include 1) the added time and labor necessary for placing and removing implants and 2) conception rates are generally low with the progestogen system.

B. Melengesterol Acetate (MGA)

The use of MGA is also a progestogen based system. This product is currently labeled for use in heat suppression in feedlot steers and has been used with increased frequency in recent years to synchronize breeding females. Per the FDA regulations MGA can be fed at a rate of .5 mg per head per day to suppress estrus. Once MGA is removed from the feed, females can be expected to begin cycling within a few days, normally two to three. Current research indicates that greater conception rates are realized if breeding is postponed to the second cycle after breeding, not the one immediately after feeding and withdrawal of the compound.

The Program

As with the previous program discussed, MGA feeding also requires some advance planning. Once again you need to decide when in the future you want a synchronized heat. Eleven to 14 days prior to this date you will need to:

a) begin feeding MGA at the prescribed level in a feed product the cattle will consume. Be sure to feed at all level that ALL the feed is consumed at one time to insure intake.

b) Continue feeding for 11 to 14 days.

c) At this point remove the MGA from the feed

d) After 48 to 72 hours breed-ing can begin, although as discussed, it is normally preferable to wait until the next cycle so fertility will be increased. This simply allows more time for the MGA to clear the system.

e) Introduce clean-up bulls into the herd

The advantages of this program include simplicity and reduced handling of the cattle. Unfortunately the disadvantage is that this is not as exact as other programs and may not group the cattle quite as tightly.

Other Programs

In the next issue (after the first of the year) we'll continue this discussion with the Prostaglandin programs mentioned previously.

I'd like to take a moment to wish each and every one of you a very Merry Christmas and a blessed New Year. I want to tell you how much I appreciate the notes, e-mails and calls I get from you and the many words of encouragement. I look forward to the coming year and to hearing from you at any time. Happy holidays from the Blezingers; Steve, Linda, Drew, Shelby and Kasey!

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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