Understanding the “Stand-to-Be-Mounted” (STBM) Behavior in Cows: A Key Indicator of Estrus
Effective estrus detection is crucial for successful breeding programs in cattle. One of the most reliable indicators of estrus, or “standing heat,” is the “stand-to-be-mounted” behavior exhibited by cows. Recognizing and understanding this behavior is essential for timely artificial insemination (AI) and optimizing reproductive efficiency.
The Estrous Cycle in Cattle
Cows are polyestrous animals, experiencing regular estrous cycles throughout the year. The average cycle length is approximately 21 days, though it can range from 17 to 24 days. Each cycle comprises several stages:
- Proestrus: Characterized by follicular growth and rising estrogen levels.
- Estrus: The period of sexual receptivity, commonly referred to as “standing heat.”
- Metestrus: Post-ovulation phase where the corpus luteum forms.
- Diestrus: A phase of sustained progesterone production by the corpus luteum.
“Stand-to-Be-Mounted” Behavior
The hallmark sign of estrus in cows is their willingness to stand immobile while being mounted by other cows or bulls. This behavior, known as “standing estrus,” indicates that the cow is sexually receptive and at the optimal time for breeding.
Key aspects include:
Duration: Standing estrus typically lasts about 12 to 18 hours but can vary between 6 to 24 hours.
- Observation: Cows in standing estrus may also attempt to mount other cows. However, only the cow that stands to be mounted is considered to be in true estrus.
- Secondary Signs of Estrus
While the stand-to-be-mounted behavior is the primary indicator, cows may exhibit additional signs during estrus:
Increased Activity: Restlessness and frequent movement.
- Mounting Others: Attempting to mount other cows, though this alone doesn’t confirm estrus.
- Vocalization: Increased mooing or bellowing.
- Mucus Discharge: Clear mucus visible around the vulva.
- Swollen Vulva: Slight enlargement or reddening.
Importance of Accurate Estrus Detection
Timely and accurate detection of estrus is vital for:
- Artificial Insemination (AI): Ensuring AI is performed during the optimal fertility window, which is approximately 12 hours after the onset of standing estrus. Reproductive Efficiency: Reducing open days and improving calving intervals.
- Economic Benefits: Enhancing milk production and overall profitability by maintaining optimal breeding schedules.
Challenges in Detecting Standing Estrus
Several factors can hinder the observation of standing estrus:
- Short Duration: The brief period of standing estrus necessitates frequent monitoring.
- Nocturnal Activity: Cows often exhibit estrus behaviors during nighttime or early morning hours.
- Environmental Factors: Heat stress, slippery flooring, or overcrowding can suppress estrus behaviors.
Enhancing Estrus Detection
To improve the accuracy of estrus detection:
- Regular Observation: Monitor cows multiple times daily, especially during dawn and dusk.
- Use of Detection Aids: Employ tools like tail paint, pressure-sensitive devices, or activity monitors to identify estrus behaviors.
- Record Keeping: Maintain detailed records of each cow’s estrous cycle to predict and anticipate estrus periods.
Signs of Heat
It is essential to understand the primary and secondary signs of heat in order to achieve accurate and efficient heat detection.
Primary sign
A cow standing to be mounted is the most accurate sign of estrus. Standing heat is the most sexually intensive period of the estrous cycle. During this period, cows stand to be mounted by other cows or move forward slightly with the weight of the mounting cow. Cows that move away quickly when a mount is attempted are not in true estrus. In order for standing behavior to be expressed, cattle obviously must be allowed to interact.
The expression of heat is due to the elevated level of estrogen in the blood when progesterone is very low. Occasionally cows in early pregnancy, approaching the end of pregnancy, or with ovarian follicular cysts have similar hormonal relationships and may express signs of heat.
The average duration of standing heat is 15 to 18 hours, but heat duration may vary from 8 to 30 hours among cows. An estrous cow usually stands to be mounted 20 to 55 times during her estrous period. Each mount lasts three to seven seconds. Factors that affect expression of heat are discussed in a later section.
Secondary signs
Secondary signs vary in duration and intensity. These signs may occur before, during, or after standing heat and are not related to time of ovulation. Dairy producers should use these signs as clues or watch the specific cow more closely for standing behavior. To determine whether cows exhibiting secondary signs will stand to be mounted, they may be isolated with a sexually active cow or teaser animal.
Mounting Other Cows
Cattle that exhibit this behavior may be in heat or approaching heat. Mounting activity is performed much less frequently by cows in midcycle. Although mounting cannot be used as a true primary sign of heat, cows exhibiting such behavior should be watched closely for standing behavior.
Mucus Discharge
As an indirect result of elevated estrogen levels, mucus is produced in the cervix and accumulates with other fluids in the vagina before, during, and shortly after estrus. Long viscous, clear elastic strands of mucus generally hang from the vulva. Sometimes, however, the mucus does not appear externally until the cow is palpated during insemination and the mucus is expelled. Mucus also may be smeared on the tail, thighs, flanks, or perineal region.
Swelling and Reddening of the Vulva
During heat the vulva swells and the interior becomes moist and red. Generally these symptoms appear before heat and remain for a short period after heat. Thus they are not precise indicators of estrus. During midcycle the lips of the vulva are pale and more difficult to separate.
Bellowing, Restlessness, and Trailing
Cows in heat are more restless and alert to their surroundings. When allowed to interact with other cattle, cows coming into heat “proestrus” and cows in heat persistently trail behind to try to mount other cows. Research shows that cows in heat spend less time resting than nonestrous herdmates. Prior to and during heat, they remain standing and alert while their herdmates are lying down and resting. This is more noticeable for stanchioned cows. Cattle may bellow more frequently during estrus. Although these are not definitive signs of heat, cows exhibiting such behavior should be watched closely for standing behavior.
Rubbed Tailhead Hair and Dirty Flanks
As a consequence of being ridden, the hair on the tailhead and rump is fluffed-up, rubbed, or matted, and the skin may be exposed. The legs and flanks may be smeared with mud or manure.
Chin Resting and Back Rubbing
Prior to mounting, cows often rest or rub their chin on the rump or back of the cow to be mounted. This application of pressure may be considered a test for receptivity to being mounted. Both cows should be observed closely for mounting and standing behavior.
Sniffing Genitalia
Sniffing the genitalia and licking the vulva of other cows occur much more frequently with cows in proestrus and estrus.
Head Raising and Lip Curling
Generally this activity follows sniffing of the genitalia and occurs more frequently if the cow being investigated is in heat and urinates.
Decreased Feed Intake and Milk Yield
Estrous cows spend less time feeding. Some studies also have reported decreased milk yield during estrus, and a Canadian study reported a slight increase in milk yield toward the end of heat. But since many factors other than estrus can affect milk yield on a specific day, this is not a reliable indicator of estrus.
Metestrous Bleeding
Some cows and most heifers have a bloody mucus discharge one to three days after estrus, but onset of this symptom, called metestrous bleeding, is quite variable. High estrogen levels during estrus cause blood to leak from vessels near the surface of the uterus. This discharge indicates that the cow was in heat and does not mean that she failed to conceive. However, such animals should be watched closely for a return to heat in 18 or 19 days.
In dairy and beef cattle management, reproductive efficiency is crucial for profitability and herd productivity. One of the most reliable signs of estrus (heat) in cows is the stand-to-be-mounted (STBM) behavior—when a cow stands still and allows other cows to mount her.
Why Is Stand-to-Be-Mounted Behavior Important?
Accurate Heat Detection: STBM is the most definitive sign that a cow is in heat, helping farmers and breeders time artificial insemination (AI) for maximum conception rates.
Improved Fertility Management: Identifying heat early reduces missed breeding opportunities and calving intervals.
Better Herd Health Monitoring: Understanding this behavior can also signal hormonal balance and reproductive health in the herd.
Key Observations of STBM Behavior:
Cows in estrus stand still when mounted by another cow.
Mounting behavior typically lasts 4-6 seconds per interaction.
Heat-active cows often have increased restlessness, vocalization, and clear mucus discharge.
The best time to observe heat behaviors is during early morning and late evening when cows are most active.
Enhancing Heat Detection Efficiency:
Use of Heat Detection Aids: Tail chalk, pedometers, and electronic activity monitors help track mounting behaviors.
Frequent Observation: Checking cows at least 3-5 times daily improves heat detection accuracy.
Maintaining a Stress-Free Environment: Proper nutrition, comfort, and space allow natural estrus behaviors to be expressed clearly.
Recognizing the stand-to-be-mounted behavior is fundamental for effective estrus detection in cattle. By understanding and monitoring this primary sign, along with secondary indicators, producers can enhance reproductive management, leading to improved fertility rates and economic returns.
