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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

The Cow-Calf Manager:
Managing Natural Service and Artificial Insemination

Livestock Update, April 1998

John B. Hall, Animal and Poultry Sciences, Virginia Tech

By breeding time, calving season is over, the grass is green and the weather is warmer. A great time to be in the cattle business. Often our attention is pulled towards spring planting, equipment repairs or the kids' ball games rather than the cattle operation. It's tempting to open the gate, let the bull in and say "go to it boy". But the breeding season, especially the early part, deserves our attention whether we're using AI or natural service. We need to manage the breeding season just like any other critical portion of the beef operation. The success or failure of this management will be realized nine months from now.

Last month we emphasized pre-breeding nutrition and examinations, now lets look at some other management considerations for the breeding season.

Natural Service

Bull to cow ratios
Research indicates that we can run more cows per bull. For years, we used the blanket recommendation of 25 to 30 cows per bull and limit yearling bulls to 20 cows per bull. But research indicates that we could go as high as 60 cows per mature bull. My current recommendation for bulls age 2 and up is one bull for every 40 cows. Research from Georgia demonstrated no difference in conception rates for bulls bred to 25 cows or 40 cows in a 90-day breeding season (Figure 1). There also was no difference between 2 year-old and 3 year-old bulls in their ability to breed 40 cows.

It is essential that bulls pass a complete breeding soundness exam before being turned out. Yearling bulls should be limited to no more than 30 cows.

Although most Virginia beef herds need only one or two bulls, some large herds use several sires in the same pasture with large numbers (100+) cows. Many producers believe this gives them insurance against sub-fertile bulls. However, the dominant bull will always breed most of the cows and defend his "right" to do so. If the dominant bull is sterile, this can mean poor conception and pregnancy rates for the herd. If multi-sire breeding groups are going to be used, bulls should be age and size matched. If young bulls are placed with older bulls the young bulls will only sire about 25 % of the calves. In addition, he usually becomes a punching bag for the older bull. Bulls from multi-sire groups usually have more injuries including broken penises and tend to leave the herd sooner.

Monitor Bull and Cow Performance
Bull performance should be monitored for the first 5 days of the breeding season. Producers need to watch bulls and cows closely for the following:

  1. Are bulls finding and mounting cows in heat?
  2. Do bulls actually service cows upon mounting?
  3. Once a bull has serviced a cow does he move on to the next cow in heat?
  4. How many cows have been in heat in the first 5 days of the breeding season?

Bulls should be able to find, mount and service cows in heat efficiently. Remember when cows first come into heat they sometimes stand for other cows but not for the bull. Cows should stand for the bull by the middle of heat. Once a bull has serviced a cow once or twice he should move on and attempt to service other cows that are in heat.

Approximately one fourth (1/4) of the herd should be in heat during a 5-day period. This rate usually varies from 15 to 35 % in normal herds with a large percentage of cycling cows. If only 5 to 10 % of cows are in heat, there may be a low percentage of cows that are cycling and producers may need to consider some alternative management practices. These alternative management practices may include: synchronization with Syncro-mate B or MGA, calf removal, or increased nutrition. These practices may be used alone or in combination.

Cows should also be observed for 5 days starting about 19 days after the bulls were turned out. If a large percentage of cows that were in heat and bred are in heat again, there may be a problem with the bull.

Bull Nutrition
I have covered different aspects of cow nutrition over the last few months. Nutrition of the bull is no less important. Bulls need to be in body condition score 5 at the start of the breeding season. They should be no thinner than BCS 4 by the end of the breeding season. Bulls may need additional energy supplementation during the breeding season to maintain body condition and fertility. It is especially important for yearling bulls to receive extra energy during the breeding season. Finding and breeding large numbers of cows requires a lot of energy.

Estrous Synchronization and Natural Mating
Estrous synchronization can be used effectively with natural mating as long as the synchronized estrus occurs 13 to 14 days before the bulls are turned in. In Kentucky, we fed MGA (0.5 mg/head/day) to heifers for 14 days then turned the bull in 13 days after the last feeding of MGA. In 601 heifers from 12 herds, we had a 69% conception rate to the first heat after we turned in the bull. These systems work well for heifers. Information on this system is available from your extension office.

Artificial Insemination

Producers interested in artificial insemination may want to get a copy of two new handouts called "Managing Artificial Insemination in Beef Herd" and "Estrous Synchronization Systems for Artificial Insemination and Natural Service". Contact your local extension office for a copy.

In order to start or improve a beef AI program, producers should do the following:

  1. Analyze your interest and attitude towards using AI in your herd
  2. Check the nutritional program and status of your herd
  3. Evaluate your facilities
  4. Decide on an AI system
  5. Review estrus detection and learn ways to reduce detection time
  6. Check your cattle handling practices
  7. Take an AI course or refresher workshop

Attitude and Commitment
Without a doubt, a positive attitude and extreme commitment are the most important management tools needed for successful AI. There is no reason to even consider AI if you are only going to make a half-hearted attempt. Producers with a negative attitude to AI are destine to fail.

In addition to time and labor, some new costs (see Table 1) are associated with AI. Often reducing the number of bulls used for natural service offsets these costs. Added value of the calves usually makes AI a profitable addition to a beef breeding program.

Table 1. Cost comparison of breeding systems

 Breeding System
Natural Service21 day AI, no synchronization, clean-up bull 21 day AI w/ synchronization, clean-up bull70 day AI, no clean-up bull
Breeding cost per pregnant female (100 cow herd)$ 32.00$ 32.10$ 38.50$ 40.00
From Nebraska data

Good Estrus Detection (Checking Heat) Is the Key to Successful AI

Without good estrus detection it doesn't matter how good an inseminator is; cows just won't conceive. Cows ovulate approximately 24 to 30 hours after the beginning of estrus or 12 - 14 hours after the end of estrus. However, semen must be deposited in the female reproductive tract several hours before ovulation to insure high conception rates. Cows remain in estrus for 8 - 16 hours.

The average life span of an ovum (egg) in the female reproductive tract is about 8-12 hours. The life span of sperm in the reproductive tract is about 30 - 48 hours. Therefore, it's better to inseminate too early rather than too late. However, on time is the best. Breed 12 hours after you first see the cow in heat.

Follow the old a.m. - p.m. rule - If in heat in the morning before noon, breed the cow that p.m. In heat in the afternoon or evening, breed the next morning.

Cows should be checked at least twice a day at dawn and dusk. This will catch 80-90 % of the cows that show heat. Additional heat checks will increase the number of cows you find in heat, but usually the extra time is not justified in a beef operation. DO NOT check heat on cows at feeding time. When eating, cows are not interested in expressing estrus.

Tip - Using binoculars will make reading ear tags easier without disturbing cows.

Weather and environment can greatly impact expression of estrus in cows.

Estrous synchronization
Beef producers should use estrous synchronization. Without a doubt an AI program in a beef herd will be difficult and too time consuming if estrous synchronization is not used. Simply this reduces the intensive heat check period from 21 to 5-7 days. Many beef AI programs have worked without estrous synchronization; however, it is a very labor-intensive method to operate an AI program. Consult the publication "Estrous Synchronization for AI and Natural Service", your local veterinarian or extension professional for information on estrous synchronization.

Estrus detection aids
Producers should seriously consider using one of several heat detection aids available today. These assist the producer in identifying cows in heat more rapidly and can also indicate cows that expressed estrus between the normal heat check times. I also recommend breeding based on these aids. Occasionally it costs some semen but often cows conceive that would otherwise be missed.

Remember these are just aids - THEY DO NOT REPLACE VISUAL HEAT DETECTION.

Care must be used in interpreting the results of these aids to reduce false positives.

Estrus detection aids include Kmar patches, Bovine Beacons, Chin ball markers, Marking harnesses, Electronic heat checking devices (Heat Watch) or Marker animals. For most beef operations, marker animals along with marking devices or patches are the most efficient and economical detection aid.

For more information on estrus detection aids consult "Managing Artificial Insemination in Beef Herds", contact your extension office or give me a call.

Some Tips For Handling Cattle For AI

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