Heat Detection with Cattle

Effective reproductive management in a dairy herd requires a combination of conscientious heat detection and proper timing of artificial insemination (AI). Failure to accurately detect estrus (heat) is a surefire precursor to poor success rates with AI. With a focus on efficient heat detection and well-timed breeding, a dairy can realize economic benefits with reduced breeding expenses and calving intervals. To help with the task of heat detection, there are a variety of helpful tools and protocols available.

This article provides information on characteristics of the estrous cycle, signs of estrus, factors affecting expression of estrus, common tools that help with heat detection, and general suggestions for managing heat detection.

Characteristics of the Estrous Cycle

In normal heifers and cows, there are two main structures commonly found on their ovaries, a corpus luteum (CL) and follicles of various sizes. The presence and size of these structures is constantly changing, especially in non-pregnant animals, and the hormones produced by them are important for many aspects of reproductive function.

Mature females typically have two or three groups of follicles that develop during each estrous cycle. Most of the time, a single follicle within each growing group becomes dominant and ends up suppressing the continued growth of the other follicles within that group. This gives these follicles a wave-like pattern of growth. With the constant changes, populations of small, medium, and large follicles are present on the ovaries at almost any given time during the estrous cycle.

In a high progesterone environment, even the dominant follicle of a follicular wave will eventually die and regress. However, when progesterone is low, the dominant follicle will usually continue to grow.

On about Day 18 of a normal 21-day cycle, the CL that developed after the previous ovulation begins to regress and circulating progesterone concentrations decline. The dominant follicle of the follicular wave continues to increase in size and eventually produces high levels of estrogen, the other prominent hormone produced from ovaries. Since progesterone concentrations are low, estrogen causes the characteristic signs and behavior associated with estrus. Estrogen also initiates the release of a surge of luteinizing hormone (LH) from the pituitary gland, a key event leading to ovulation. The onset of estrus defines the beginning of a new estrous cycle (Day 0).

Luteinizing hormone starts the process of ovulation, which occurs, on average, about 28 hours after the onset of standing estrus. At the site of ovulation, the remaining follicular cells are transformed into a CL. The CL increases in size over the period of several days and produces increasing amounts of progesterone. Circulating concentrations of progesterone are high from about Day 6 through Day 18 of the cycle. Although follicles continue to develop and produce low levels of estrogen during midcycle, the high level of progesterone prevents their final maturation and inhibits expression of estrus. Eventually these larger follicles degenerate and estrogen production declines.

Progesterone also prepares the uterus for pregnancy, inhibits uterine contractions, and maintains pregnancy. If pregnancy is established, the CL does not regress, and progesterone levels remain elevated throughout pregnancy. Normal estrous cycles only continue to occur with non-pregnant females.

Figure 2 illustrates the structural changes on the ovaries and progesterone concentrations during an estrous cycle with two waves of follicular development. Although specific days of the cycle are indicated, it is important to realize there is variation from animal to animal and cycle to cycle.

Figure 2. Ovarian activity during the estrous cycle, representing changes on both ovaries. The light orange curve represents circulating progesterone, originating from one or more corpus luteum (CL). The yellow circles represent growing follicles. The red circles represent regressing follicles. The large, bursting follicles at the far left and far right represent ovulation, releasing a small oocyte from within the follicle. Notice that on any given day there is typically a mixture of growing and regressing follicles, with the sizes changing each day.

Signs of Heat

Figure 3. Standing and mounting activity (Photo credit: Andrew Sandeen, Penn State Extension)

In the majority of cases, there are significant behavioral changes that can be observed in heifers and cows when they are in estrus (heat). The intensity and length of time they are in heat can vary from animal to animal and farm to farm, but the signs are consistent.

Primary sign

The most useful and accurate sign of estrus is when a cow stands to be mounted. Standing heat is a brief but intense period of the estrous cycle characterized by behavior distinctly different from the other 95% of the cycle. Cows typically stand still as they are mounted by other cows or move forward just slightly with the weight of the mounting cow. If a cow moves away quickly when a mount is attempted, she is probably not in true estrus.

The expression of heat is due to the elevated level of estrogen in the blood when progesterone is very low. Occasionally, cows that are pregnant or have ovarian follicular cysts will have similar hormonal relationships and exhibit signs of heat, but most of the time these signs are indicative that a heifer or cow is not pregnant and cycling.

In a research study from several years ago (Walker et al., 1996), pressure-sensitive sensors were used to monitor the mounting activity of Holstein cows. On average, the entire duration of estrus from first mount to last mount was 9.5 hours, with 10.1 total mounts. Interestingly, the cumulative amount of time when a mount was occurring over the span of the estrus period was, on average, 24.1 seconds. Standing activity can easily be missed.

More recently, using activity monitoring systems, researchers found the average duration of elevated activity in lactating Holsteins around the time of estrus to be 13.5 hours, while actual standing activity only lasted for 6.3 hours, with 10.3 standing events per estrus (Schilkowskey et al., 2021). In two other studies, the duration of estrus as measured with an activity monitoring system was 11.2 hours (Madureira et al., 2015) or 14.9 hours (Tippenhauer et al., 2021).

Secondary signs

Secondary signs of estrus vary in duration and intensity. These signs may occur before, during, or after standing heat and are not as reliable or accurate, especially in terms of predicting the timing of ovulation for the purpose of timely AI. These signs are best used as clues or an indication of when to watch a specific animal more closely for standing behavior.

Mounting other cows

It is common to observe a busy group of heifers or cows trying to mount each other. The details are important. Females exhibiting this behavior may or may not be in heat. They will oftentimes show interest in riding before coming into a standing heat, and the riding activity may continue beyond the time of their standing heat. Efforts to ride another animal should not be used as a primary sign of heat, but heifers or cows exhibiting such behavior should be watched closely for actual standing behavior.

Bellowing, restlessness, and trailing

When allowed to interact with other cattle, females in heat or soon to be in heat persistently trail behind other cows, frequently trying to mount them. They spend less time resting than their pregnant or non-estrous herdmates. They may also bellow more frequently. Although these are not definitive signs of heat, females exhibiting such behavior should be watched closely for standing behavior.

Activity monitoring systems are now commonly used in dairy herds to monitor heat detection around the clock by measuring the movement of individual animals through the day and identifying when activity has exceeded an established threshold for normal activity. Though activity monitors don’t identify standing estrus events specifically, they have proven reliable enough to detect heat and determine a time window for when to perform AI.

Stevenson et al. (2021) observed that, on the day of estrus, cows rested three hours less than on other days of their cycle. Stevenson et al. (2014) monitored estrous activity in U.S. Holstein cows and observed the following, on average, for each individual estrus event:

• Duration of estrus (standing to be mounted): 7.1 hours
• Duration of increased activity: 13.0 hours
• Total number of standing events: 5.9
  
  

Chin resting

Amongst other estrus activity, heifers or cows will often rest or rub their chin on the rump or back of another heifer or cow. This application of pressure may be a test for receptivity to being mounted. Both animals should be observed closely for mounting and standing behavior.

Figure 4. Chin resting activity (Photo credit: Andrew Sandeen, Penn State Extension)

Sniffing genitalia and lip curling

Sniffing genitalia and licking the vulva of other cows occurs much more frequently with cows in estrus. Especially if the cow being sniffed is in heat, the sniffing is oftentimes followed by lip curling, like what a live bull will do if he is around females in heat. She will raise her head and pull her lips back in dramatic fashion.

Mucus discharge

As an indirect result of elevated estrogen levels, mucus is produced in the cervix, and some of it drains from the vagina before, during, and shortly after estrus. Viscous strands of clear mucus can often be observed hanging from the vulva. Sometimes, however, the mucus does not appear externally until the cow is palpated during insemination and some of the mucus is expelled. Mucus may also be found smeared on the tail or any place on the side of the animal that the tail might take it to.

Figure 5. String of clear mucus hanging externally from the vulva (Photo credit: Dr. Rob Lofstedt, Library of Reproduction Illustrations)

Swollen, red vulva

A heifer or cow’s vulva swells during estrus. The interior becomes moist and red. Generally, these symptoms appear before estrus and remain for a short period after estrus. They can easily be misinterpreted and are not precise indicators of estrus.

Rubbed tailhead

As a consequence of being mounted and ridden, the hair on the tailhead and rump often gets fluffed-up, rubbed, or matted. Especially when combined with other secondary signs, this can be a good indicator of recent mounting activity and probable estrus.

Decreased feed intake and milk yield

Cows in estrus spend less time feeding and ruminating, which may be detected with an activity monitoring system. They may also have decreased milk yield. However, since many factors other than estrus can affect milk yield and feeding activity on a specific day, these are not reliable indicators of estrus.

Metestrous bleeding

Some heifers and cows have a bloody mucus discharge visible on the vulva one to three days after estrus, called metestrous bleeding. This discharge indicates that the cow was recently in heat and the time of eligibility for AI has passed, but this does not mean that she failed to conceive if she was inseminated. If eligible for breeding, she should be watched closely for a return to heat in 18 or 19 days.

Factors Affecting Estrous Behavior

Figure 6. Crowding (Photo credit: Andrew Sandeen, Penn State Extension)

There are a variety of factors that can affect expression of estrus. Each heifer or cow is an individual and has specific factors, whether health-related or not, which affect her activity. There are also factors from the environment where cattle are living or spending significant amounts of time. Management decisions and strategies will impact what heat activity can be observed. All these challenges, individually or collectively, can hamper reproductive performance.

Type of housing

Any housing arrangement that allows cattle to interact freely throughout the day provides opportunity for mounting and standing behavior to be expressed. Cattle housed in tie-stall or stanchion barns need to be turned out for this behavior to be expressed well.

Animals that spend significant time outdoors may have more opportunity for expression of estrus, but wet or sloped conditions can have a negative impact. It may also be a challenge for visual observation of estrus if the cattle have access to a large area away from where farm personnel are typically working.

Figure 7. Cows on pasture with good footing (Photo credit: Andrew Sandeen, Penn State Extension)

Footing surface

In general, mounting and standing estrus behavior tends to be better when animals are standing on dirt as compared to concrete, though there are many different factors that can add or subtract to the likelihood of good estrus expression. For example, wet or icy conditions can dramatically affect the ease of moving around and showing signs of estrus. If the animals do spend significant time on concrete, managing the open spaces to promote good traction (e.g., adequate grooving in the concrete) will improve opportunities for normal expression of estrus.

Figure 8. Cow standing on grooved concrete (Photo credit: Andrew Sandeen, Penn State Extension)

Feet and leg problems

Sore feet or legs or poor structural conformation often lead to less mounting activity. It is also possible to see increased activity around a cow with mobility issues which cannot easily move when mounted. These issues will hamper any heat detection program.

Cow density

If cattle are forced into a crowded area such as a holding pen connected to a milking parlor, mounting activity will most likely be suppressed or cows will be forced to stand to be mounted even when they are not in heat. Overcrowding in other areas of a facility may lead to other issues (e.g., feet and leg problems) that will eventually impact heat detection efficiency.

Temperature

In cold weather, cows exhibit more mounting activity than when in hot weather conditions. In general, heat stress causes a reduction in mounting and standing activity, as well as other secondary signs of estrus, making visual detection of estrus more difficult. For example, Tippenhauer et al. (2021) found that when the temperature humidity index was above 60, duration and intensity of estrus declined, with even more dramatic effects when it was above 70.

Herdmate status

To determine the cause of silent heats or poor expression of heat, consider the overall reproductive status of the herd and compare the ratio of open to pregnant animals in each group. Pregnant cows are the least likely group of herdmates to mount a cow in heat. Herd managers must rely on the other open cycling herdmates to detect heat. In some herd situations, having few open cycling cows in a group may also contribute to the problem of silent or missed heats.

There may be situational extremes for herds that freshen on a seasonal basis. After an intensive breeding period, when a high percentage of the herd is pregnant and estrous detection may be easy, it later becomes increasingly difficult to identify the few open, cycling cows in heat. There may not be enough herdmates in the proper stage of the cycle to interact with a cow in heat.

A third situation may occur frequently in free-stall herds where cows are grouped according to production. Generally, the lower production group contains pregnant cows, but because of low production, some nonpregnant cycling cows may be included in this group. It becomes very difficult to detect the cows in heat because their herdmates are pregnant.

Milk production

Though there is some variation in research results, it is common for high milk production to lead to a decline in the duration of estrus and intensity of estrous activity as compared to lower-producing cows in the same herd (Lopez et al., 2004; Madureira et al., 2015; Schilkowskey et al., 2021; Stevenson, 2021). Specifically, Lopez et al. (2004) found that high-producing cows had a shorter duration of estrus (6.2 vs. 10.9 hours) and fewer standing events (6.3 vs. 8.8) when compared to the lower-producing cows.

Age

Older cows tend to show less activity over a shorter period of time than young cows (Madureira et al., 2015). Stevenson et al. (2021) found that primiparous cows were more active than multiparous cows, with 36 more minutes of high activity on the day of estrus compared with multiparous cows. Young, lower-producing cows are generally the easiest ones to catch in heat.

Anovulation

Anovulation, which literally means "the absence of ovulation," is a phase that fresh cows go through and sometimes return to after ovulating once or twice. The duration of the phase is quite variable. Some cows will ovulate and start cycling normally in the first few weeks; for others, first ovulation might be delayed for a much longer period of time. It is not uncommon for anovulation to persist more than two or three months, especially in situations with low body condition, negative energy balance, or other postpartum health disorders. During this time of noncyclicity, it is unlikely that there will be any normal heat activity.

Estrous Detection Aids

 

Figure 9. Cow with large, clear ear tag for easy identification (Photo credit: Andrew Sandeen, Penn State Extension)

Tailhead Markings

Marking the tailhead with chalk, paint, or crayon and observing for evidence of rubbed off or smeared markings can be quick, easy, and requiring minimal expense. Markings 10 to 12 inches long and 2 to 3 inches wide are made across the tailhead with a livestock marking crayon or heat detector paint. This system works most effectively in loose-housing arrangements where cattle can be restrained in self-locking headgates. Markings can be observed at least once every day and refreshed, as necessary. When the colored material has been rubbed off, there is a good chance the animal has recently been mounted at least once, but false positives can occur. With experience, observing the markings and looking for other secondary signs of estrus can be an effective approach to heat detection.

Tailhead Patches

There are a variety of patches and devices that can be adhered to the topline of the rump. Some change color after a period of direct, sustained pressure. Others change color as they are rubbed, allowing for an interpretation of how much rubbing and/or mounting activity there has been.

Activity monitors

It is well documented that cattle are more active during estrus and thus spend more time walking and standing than resting. They also tend to ruminate (chew their cud) less. There are a variety of technological tools available for dairy farms, monitoring these behavioral activities on individual heifers and cows around the clock. Devices are commonly worn on the neck or as an ear tag, sending data to a central computer.

Of note, activity monitors can be useful for identifying cows which fail to show obvious signs of estrus that would not prompt a response with traditional heat detection. Use of activity monitors can also lessen the amount of time animals need to be locked up each day for reproductive evaluations. One caution is that changes in management activities that prompt excessive cow activity (e.g., moving pens) can temporarily cause inaccurate readings.

Prostaglandin F_2α

There are a number of prostaglandin F_2α (PGF) products commonly used on dairy farms for managing reproduction. Estrous synchronization is one of the common strategies, where use of one or more PGF treatments will narrow the window of expected heats to just a few days, rather than the full spectrum of 21+ days. Additionally, PGF is one of the key treatments used in timed AI protocols, which can effectively eliminate the need for heat detection altogether, at least during the final stages of the timed AI protocol.

Heat Detection Management Tips

Figure 10. Keep a close eye on data (Photo credit: Andrew Sandeen, Penn State Extension)

Records

• Record all heats, whether the animal is to be inseminated or not, which may prove valuable when future heats can be anticipated. It will also allow for monitoring and response to abnormally long cycles and long intervals from freshening to conception.
• Use a pocket notebook or mobile device to record heats and other information.
• If multiple employees have reproductive management responsibilities, make sure everyone understands the system and is collecting meaningful and comprehensible records that can be easily shared.
• Make sure every animal can be easily identified.

Analysis & troubleshooting

• Monitor whether heats are being observed and recorded before the first service. If not, determine whether cows are returning to cyclicity soon enough or if workers are keeping records of all heats.
• Generally, heat detection rate for the lactating herd should be at or above 65%. Heat detection rate is a measurement of the percentage of the eligible cows that were detected in heat over a certain period of time. Submission rate is a similar term that might be more relevant for herds relying primarily on timed AI. However, submission rate might not account for recognized heats when AI was not performed.
• Aim for the average days to first service to be less than 20 days beyond the designated voluntary waiting period.
• Strive to see at least 60% of the estrous intervals between services at 18 to 24 days.

Employees

• Provide introductory training for those just starting to take on reproduction-related responsibilities. Include clear explanations of what to expect, how to interpret estrous activity, and the importance of these responsibilities on the dairy. If possible, communicate in a language that is well understood.
• Provide workers inexperienced with reproduction-related responsibilities ample opportunity to discuss and work out their various questions and struggles with understanding estrous activity.
• If multiple workers are involved in reproductive management, have regular meetings to discuss how things are going and refresh important points related to reproduction.
• Provide clear expectations for what records to keep and how to share them.

General recommendations

• Watch for sexually active groups of cattle. Cows in or near the period of estrus tend to congregate and stay together.
• Consider using heat detection aids to help increase the number of heats detected. Detection tools should supplement routine visual observation.
• Stay aware of environmental challenges and make positive adjustments whenever feasible.
• Consider timed AI as a tool. It eliminates some of the need for heat detection, but it also necessitates extra labor, supplies, injections, and lock-up time. Timed AI can pair nicely with heat detection for a comprehensive and effective reproduction program for all eligible females on the dairy.
  
  

Enjoy seeing new pregnancies established and calves born into the operation!

Some of the material of this article was developed from a previous publication titled, “Heat Detection and Timing of Insemination for Cattle,” written by Dr. Michael O’Connor.

The content of this document, including text, graphics, and images, is educational only and not intended to be a substitute for veterinary medical advice, diagnosis, or treatment. Always seek the advice of a licensed doctor of veterinary medicine or other licensed or certified veterinary medical professional with any questions you may have regarding a veterinary medical condition or symptom.

References

Lopez, H., Satter, L. D., & Wiltbank, M. C. (2004). Relationship between level of milk production and estrous behavior of lactating dairy cows. Animal Reproduction Science, 81, 209–223.

Madureira, A. M. L., Silper, B. F., Burnett, T. A., Polsky, L., Cruppe, L. H., Veira, D. M., Vasconcelos, J. L. M., & Cerri, R. L. A. (2015). Factors affecting expression of estrus measured by activity monitors and conception risk of lactating dairy cows. Journal of Dairy Science, 98, 7003–7014.

O’Connor, M. L. (1993). Heat detection and timing of insemination for cattle. Penn State Extension Circular 402.

Schilkowsky, E. M., Granados, G. E., Sitko, E. M., Masello, M., Perez, M. M., & Giordano, J. O. (2021). Evaluation and characterization of estrus alerts and behavioral parameters generated by an ear-attached accelerometer-based system for automated detection of estrus. Journal of Dairy Science, 104, 6222–6237.

Stevenson, J. S., Hill, S. L., Nebel, R. L., & DeJarnette, J. M. (2014). Ovulation timing and conception risk after automated activity monitoring in lactating dairy cows. Journal of Dairy Science, 97, 4296-4308.

Stevenson, J. S. (2021). Daily activity measures and milk yield immediately before and after a fertile estrus and during the period of expected return to estrus after insemination in dairy cows. Journal of Dairy Science, 104, 11277-11290.

Tippenhauer, C. M., Plenio, J.-L., Madureira, A. M. L., Cerri, R. L. A., Heuwieser, W., & Borchardt, S. (2021). Timing of artificial insemination using fresh or frozen semen after automated activity monitoring of estrus in lactating dairy cows. Journal of Dairy Science, 104, 3585–3595.

Walker, W. L., Nebel, R. L., & McGilliard, M. L. (1996). Time of ovulation relative to mounting activity in dairy cattle. Journal of Dairy Science, 79, 1555-1561.