Combinations of heat detection aids can improve accuracy of detection of heat in cattle. The more commonly used heat detection aids include:

Marking crayons or paints

These are used on the rump of the cow and then smeared if the cow is ridden.

Tailhead markings

The tailhead is marked in a strip two to three inches wide with chalk, heat detector paint, or crayon and observations made for evidence of rubbed off or smeared markings. Orange is often the color of choice. Tailhead paint is less convenient to use than crayon but lasts longer (up to three weeks). The oil-based paint is relatively rain-resistant and unlikely to be rubbed off in brush. Cows are re-chalked when the chalk becomes weathered and dried and no signs of riding have been evident. Beef cattle producers can tail-chalk cows at about 50 days after calving.

Pressure-sensitive pads

These devices glue to the rump of the cow and either

  • Emit a red liquid when the pad is mounted or trigger a computer-linked response to indicate the cow has been ridden
  • Are erased to show red or
  • Are computer-linked modules that can record the time and/or number of mounts that a cow receives.

Kamar pressure-sensitive mount detectors

These devices are glued on the rump of cows suspected to be in heat in the near future. Sustained pressure from the brisket or chest of mounting animals expels a red fluid from a small storage chamber into a larger visible plastic chamber turning the originally white detector to red.

Electronic mount detectors

Mount detectors detect and record legitimate mounts. Each detector is coded with the cow’s identification number, and the information is transmitted to a computer to be stored. At regular intervals during the day, the herd manager can access the information to determine which cows were mounted at a particular time.

Chin-ball markers

These are used on surgically altered bulls or hormonally treated females. The device, similar to a ball-point pen, is strapped underneath the chin of an animal expected to mount cows or heifers in heat. The ink in the chin-ball marker leaves colorful streaks on the back or rump of a cow that has been mounted.

Activity monitors or pedometers

Cattle are more active during estrus and thus spend more time walking and standing than resting.  Pedometers are used to monitor cow activity between milkings. This method can be effective in identifying some silent heat cows which fail to show other obvious signs of estrus. Changes in management activities that prompt excessive cow activity on certain days can cause inaccurate readings.

Vaginal probes

The electrical resistance (ER) of vaginal fluids decreases during proestrus and through the estrous period as a result of chemical changes in the vagina as the cow approaches the time of breeding. Several probes that measure the ER of vaginal fluids are now commercially available. Monitoring the relative changes within cows during the estrous cycle can provide the herder with additional information and can serve as a heat detection aid if cattle are probed frequently.

Heat detector animals

Normally in combination with a chin ball marker, surgically altered bulls or hormonally treated females are effective in detecting heat. If allowed to interact with the herd detector animals provide a continuous monitoring of estrous behavior. Consider using a heat detector animal for housed cows whose heat detection does not seem to be effective.

Vasectomized or surgically altered bull

A vasectomized bull or a bull with a surgically altered penis can be effective heat detectors if they are equipped with a chin-ball which marks with a bright-colored marking solution the loin and rump of cows that are mounted. Surgically altering the penis of a bull is preferred since vasectomized bulls can copulate with cows and possibly spread disease.

Testosterone-treated female

Testosterone, a male hormone, causes increased sexual aggressiveness when injected or implanted into cows or heifers. Potential non-lactating cull cows or heifers, even freemartin heifers, are used. A typical treatment regime consists of administering 200 mg of testosterone propionate intramuscularly every other day for three weeks.

Video recorders

This system can be used to continuously monitor estrous behavior. The video camera(s) are strategically positioned to monitor a large proportion of the housing area. The videotapes are reviewed daily, especially after the herd has been monitored in the evening.


No matter which record system is used, the information should be posted and available to all farm employees. The more people anticipating and watching for the heat, the more likely heat detection efficiency will be maximized. All heats, including those observed in the early postpartum period, must be recorded. Finally, record systems should be used on a daily basis.

Heat expectancy chart

Special calendars are available from artificial insemination organizations. Most charts are organized on a 21-day cycle so that future heats can be anticipated. Some herd managers mark day 19 following insemination so that the expected heat can be anticipated several days in advance.

Breeding wheel or herdex record system

These wall-mounted reproductive record systems use color-coded pins or markings to indicate reproductive events for each cow. By either turning a transparent plastic dial or sliding the plastic cover on a daily basis, future heats and reproductive events can be anticipated.

Computer generated action lists

Some dairy management computer programs can generate listings of cows that require special attention or action on a specific day. Action lists indicate cows to watch closely for return heats or cows that have not yet been observed in heat.


If more than one animal is in proestrus or estrus simultaneously, mounting behavior increases and standing behavior is more likely to be observed. Depending on herd size, it may be worthwhile to inject one or more cows with prostaglandin at various intervals during the week to induce more estrous behavior in the herd.


These aids may be used with much success under good management. But remember that these detection aids require both time and other supplies, including sometimes very expensive computer-related items. Additional time in watching for heat is recommended.

Although altered heat detection aids may indicate the cow has been ridden, changes do not necessarily mean that she has been in heat. The aids may be altered by other means, such as another cow attempting to ride her or the cow may activate the detector by rubbing on a tree or other item.

When a single heat detection aid is activated, use other signs of heat to confirm that, indeed, a cow is in heat. A combination of heat mount detectors and chalk has been used with much success in reducing errors in detection. However, both aids require daily maintenance in order to be successful.

Combinations of heat detection aids may be beneficial in decreasing the number of false positives. Although more effort is required, combinations of aids may benefit herders having problems detecting cows in heat. They may also solve problems with conception rates of cows detected incorrectly and bred at inappropriate times.

Estrous detection in the future may involve electronic monitoring of mounting activity, walking, or vaginal electrical resistance integrated into an automated telemetric system. At present visual observation supported by proper use of conventional heat detection aids is the most effective approach to estrous detection.


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