Understanding Cow Heat Cycles: Tips for Timely Breeding and Higher Conception

To achieve timely breeding and higher conception rates in your herd, closely monitor cows for primary heat signs like standing to be mounted, especially during early morning and late evening. Implement the AM/PM rule for breeding, ensure optimal nutrition, manage stress, and use reliable heat detection aids. Consistent observation and accurate record-keeping are crucial for maximizing reproductive efficiency and herd profitability.

For many cattle producers, knowing exactly when a cow is ready to breed can feel like a guessing game. Missing a cow’s heat cycle, also known as estrus, is a common and often frustrating challenge. This can lead to longer calving intervals, fewer calves, and reduced profits for your farm. But don’t worry, you’re in the right place! This article will make understanding cow heat cycles simple. We’ll walk through clear steps and practical tips to help you detect heat accurately, time your breeding perfectly, and ultimately boost your herd’s reproductive success. Let’s explore how to turn those missed opportunities into successful pregnancies, ensuring a healthier, more productive herd.

The Basics of Cow Heat Cycles (Estrus): What Every Farmer Should Know

Understanding the cow’s reproductive cycle is fundamental to any successful cattle operation, whether you’re focused on dairy or beef production. The heat cycle, or estrus cycle, is the regular pattern of physiological events that prepare a cow for pregnancy. Knowing its stages and duration is the first step toward timely breeding and improved conception rates.

What is a Heat Cycle? Understanding the Physiology

A cow’s heat cycle is a complex, hormone-driven process that typically lasts about 21 days, though it can range from 18 to 24 days. This cycle is divided into several phases, but the most critical for breeding is “estrus,” which is the period when the cow is receptive to mating.

• Estrus (Heat): This is the shortest but most vital phase, lasting an average of 12 to 18 hours. During estrus, high levels of the hormone estrogen are released from a developing follicle on the ovary. Estrogen causes the cow to display visible signs of heat and makes her receptive to breeding. Ovulation, the release of the egg from the follicle, typically occurs about 24 to 32 hours after the onset of estrus.
• Metestrus: Following estrus, the ruptured follicle transforms into a structure called the corpus luteum (CL). The CL produces progesterone, a hormone essential for maintaining pregnancy.
• Diestrus: This is the longest phase, where the CL is fully functional and progesterone levels are high. If pregnancy does not occur, the CL regresses towards the end of diestrus, allowing a new follicular wave to begin.
• Proestrus: As the CL regresses, progesterone levels drop, and a new follicle begins to develop, increasing estrogen production and leading back to estrus.

Why is Understanding it Crucial for Profitability?

Mastering heat detection and timely breeding directly impacts your farm’s bottom line. Here’s why:

• Reduced Calving Interval: The ideal calving interval for most operations is 12 to 13 months. Missing a heat cycle means delaying the next pregnancy, which lengthens this interval. A longer interval translates to fewer calves over a cow’s lifetime and reduced milk production in dairy herds.
• More Calves Per Year: Simply put, more successful pregnancies mean more calves. For beef producers, this directly increases the number of animals available for sale. For dairy producers, it ensures a steady supply of replacement heifers and consistent milk production.
• Improved Herd Genetics: Timely breeding allows you to utilize superior genetics through artificial insemination (AI) more effectively, accelerating genetic progress within your herd.
• Better Economic Returns: Every missed heat cycle costs you money in terms of lost milk production, reduced calf sales, and increased feed costs for non-productive animals. Efficient reproduction ensures your cows are productive assets, not liabilities.

Key Signs of Estrus: What to Look For

Identifying when a cow is in heat requires careful observation. While some signs are more reliable than others, combining multiple observations gives you the best chance of accurate detection.

Primary Signs (The Most Reliable Indicators)

These signs indicate that a cow is actively in estrus and ready to be bred. They are driven by high estrogen levels and reflect her receptivity.

• Standing to be Mounted: This is by far the most reliable and definitive sign of estrus. A cow in standing heat will stand still and allow other cows, heifers, or a bull to mount her. She will not attempt to move away. This behavior is a direct indicator of her physiological readiness for breeding.
• Mounting Other Cows: While less reliable than standing to be mounted, a cow actively mounting other cows can also be a strong indicator of estrus or proestrus (the phase just before estrus). Cows in heat often form “riding groups” where they interact in this manner.
• Clear, Stringy Mucus Discharge from Vulva: As estrus progresses, the cow’s cervix produces a clear, thick, stringy mucus. This discharge may be seen hanging from the vulva or smeared on the tail and hindquarters. This mucus serves to lubricate the reproductive tract and aid sperm transport.
• Swollen, Reddened Vulva: The vulva of a cow in heat often appears slightly swollen, moist, and reddish due to increased blood flow. This physical change is a visual cue of hormonal activity.

Secondary Signs (Supportive Indicators)

These signs can suggest a cow is approaching or in heat, but they are not definitive on their own. They should be used in conjunction with primary signs for confirmation.

• Restlessness and Increased Activity: Cows in heat often become more active, walking around the pen or pasture more frequently than usual. They may also appear agitated or nervous.
• Bellowing or Increased Vocalization: Some cows will vocalize more frequently or intensely when in heat, drawing attention to themselves.
• Reduced Milk Production (Dairy Cows): Dairy cows in heat often show a temporary drop in milk yield, as their energy is redirected towards reproductive behaviors and they may spend less time eating.
• Rubbed Tail Head or Dirty Flanks: If a cow has been mounted repeatedly, the hair on her tail head may be rubbed off or ruffled. Mud or manure may also be smeared on her flanks or hindquarters from other cows attempting to mount her.
• Decreased Appetite: Similar to reduced milk production, some cows may show a temporary decrease in feed intake during estrus.
• Chin Resting/Head Butting: Cows may rest their chin on the rump of another cow or engage in playful head-butting, often as part of “riding group” interactions.
• Sniffing and Licking Other Cows: Increased interest in other cows, particularly sniffing and licking their vulvas, can be a sign of a cow in heat or one approaching it.

To help visualize the difference, consider the following table:

Sign Type	Description	Reliability for Breeding
Primary Sign: Standing to be Mounted	Cow stands firm and allows another animal to mount her.	Highest (Definitive)
Primary Sign: Mounting Other Cows	Cow actively attempts to mount other cows.	High (Strong indicator, often pre-estrus or estrus)
Primary Sign: Clear Mucus Discharge	Clear, stringy mucus hanging from the vulva or on tail.	High (Indicates high estrogen, often with standing heat)
Primary Sign: Swollen, Reddened Vulva	Vulva appears enlarged, moist, and reddish.	High (Physical sign of hormonal activity)
Secondary Sign: Restlessness/Increased Activity	Pacing, increased movement, agitation.	Moderate (Supportive, but not definitive on its own)
Secondary Sign: Bellowing/Vocalization	Increased or unusual vocal sounds.	Low to Moderate (Supportive, individual variation)
Secondary Sign: Reduced Milk Production	Temporary drop in milk yield (dairy cows).	Moderate (Supportive, can be due to other factors)
Secondary Sign: Rubbed Tail Head/Dirty Flanks	Hair loss on tail head, smudges on flanks.	Moderate (Indicates previous mounting activity)
Secondary Sign: Decreased Appetite	Temporary reduction in feed intake.	Low (Supportive, but often subtle and non-specific)

The “AM/PM Rule”: Timing is Everything for Breeding Success

Once you’ve confidently identified a cow in heat, the next crucial step is knowing *when* to breed her. The timing of insemination relative to the onset of standing heat significantly impacts conception rates. This is where the widely accepted “AM/PM rule” comes into play.

Explanation of the Rule

The AM/PM rule is a practical guideline designed to maximize the chances of successful conception by timing insemination to coincide with ovulation. It’s based on the understanding that ovulation typically occurs 24 to 32 hours after the *onset* of standing heat, and the egg remains viable for fertilization for only about 6 to 12 hours. Sperm, on the other hand, need several hours to capacitate (become capable of fertilizing an egg) within the cow’s reproductive tract.

The rule states:

• If you observe a cow in standing heat in the morning (AM), you should breed her in the afternoon or evening (PM) of the same day.
• If you observe a cow in standing heat in the afternoon or evening (PM), you should breed her in the morning (AM) of the following day.

For example:

• You see Cow A standing to be mounted at 7:00 AM on Monday. Breed her between 5:00 PM and 7:00 PM on Monday.
• You see Cow B standing to be mounted at 6:00 PM on Monday. Breed her between 6:00 AM and 8:00 AM on Tuesday.

Physiological Basis: Why the AM/PM Rule Works

The AM/PM rule aims to have viable sperm present in the oviduct when the egg is released. By breeding 10-14 hours after the onset of standing heat, you allow sufficient time for sperm capacitation while ensuring the egg is still viable once it’s ovulated. This overlap maximizes the likelihood of fertilization.

Research consistently shows that following the AM/PM rule can lead to higher conception rates compared to breeding too early or too late. For instance, studies by universities like Penn State Extension and others have demonstrated that this timing optimizes the chances of pregnancy.

Importance for Conception Rates

Adhering to the AM/PM rule is a cornerstone of efficient breeding programs. It helps:

• Maximize Fertilization Success: By ensuring sperm are ready when the egg is released, you significantly increase the chances of fertilization.
• Reduce Semen Waste: Inseminating at the optimal time means you’re not wasting expensive semen on cows that are not physiologically ready or have already ovulated too long ago.
• Improve Overall Herd Reproductive Performance: Consistent application of this rule across your herd contributes to tighter calving intervals and a more productive breeding season.

While the AM/PM rule is a strong guideline, remember that individual cow variation exists. Factors like heat intensity, breed, and environmental conditions can slightly influence the ideal breeding window. However, for practical purposes, it remains the most effective and widely recommended strategy for timing artificial insemination.

Factors Influencing Heat Cycles and Fertility

A cow’s ability to express heat and conceive isn’t just about her internal hormones; it’s heavily influenced by external factors. Optimizing these areas is key to a reproductively sound herd.

Nutrition: The Foundation of Fertility

Nutrition is arguably the single most critical external factor influencing a cow’s reproductive performance. Cows need adequate energy, protein, minerals, and vitamins to cycle regularly and conceive.

• Energy Balance and Body Condition Score (BCS):
  • Underfeeding: Cows in a negative energy balance (losing weight or too thin, BCS below 4 on a 1-9 scale or 2 on a 1-5 scale) often fail to cycle or show weak, hard-to-detect heats (silent heats). Their bodies prioritize survival over reproduction.
  • Overfeeding: While less common, obesity (very high BCS) can also negatively impact fertility, leading to metabolic issues and reduced reproductive efficiency.
  • Ideal BCS: Aim for a BCS of 5-6 (on a 1-9 scale) at calving and through breeding. This indicates sufficient energy reserves for milk production and reproduction.
• Protein: Adequate protein is necessary for overall body function, hormone production, and follicular development. Deficiencies can impair reproductive function.
• Minerals and Vitamins:
  • Phosphorus: Critical for energy metabolism and reproductive processes. Deficiencies are a common cause of anestrus (absence of heat).
  • Selenium and Vitamin E: Antioxidants important for immune function and preventing reproductive disorders like retained placenta.
  • Copper and Zinc: Involved in hormone synthesis and immune response, both vital for fertility.
  • Vitamin A: Essential for maintaining healthy reproductive tissues.
• Impact of Under/Over-feeding: Both extremes can delay puberty in heifers, extend the postpartum anestrus period in cows, reduce conception rates, and increase embryonic loss. A balanced, consistent diet is paramount.

Health and Disease: Silent Fertility Killers

A healthy cow is a fertile cow. Various diseases and health issues can disrupt heat cycles and prevent conception.

• Reproductive Diseases:
  • Metritis/Endometritis: Uterine infections post-calving can delay uterine involution and prevent the cow from cycling.
  • Brucellosis, Leptospirosis, Vibriosis, Trichomoniasis: These venereal diseases can cause abortions, infertility, and irregular cycles. Vaccination and testing are crucial.
  • Bovine Viral Diarrhea (BVD): Can cause embryonic death, abortions, and congenital defects, significantly impacting herd fertility.
• General Health:
  • Lameness: Painful lameness can reduce a cow’s desire to move, making heat detection difficult and impacting her ability to breed naturally.
  • Mastitis: Severe mastitis can cause systemic illness, reducing fertility.
  • Internal Parasites: Heavy parasite loads can drain nutrients, leading to poor body condition and impaired reproduction.
• Post-Calving Recovery (Uterine Involution): The uterus needs time to return to its normal size and health after calving (typically 30-45 days). Any complications, like retained placenta or uterine infections, will delay this process and postpone the resumption of heat cycles.

Stress: A Hidden Threat to Reproduction

Stress, whether physical or psychological, can suppress reproductive hormones and interfere with normal cycling.

• Environmental Stress:
  • Heat Stress: High temperatures and humidity can reduce heat expression, decrease sperm quality in bulls, and lead to early embryonic death. Providing shade, water, and ventilation is vital.
  • Cold Stress: Extreme cold increases energy demands, potentially leading to negative energy balance and delayed cycles.
• Social Stress: Overcrowding, frequent mixing of groups, or introduction of new animals can create social hierarchies and stress, impacting reproductive behavior.
• Handling Stress: Rough handling, excessive dogging, or prolonged confinement can elevate stress hormones (cortisol), which suppress reproductive hormones.
• Transportation Stress: Moving animals, especially during critical reproductive phases, can negatively impact fertility.

Genetics: Breeding for Fertility

While environmental factors play a huge role, genetics also contribute to a cow’s inherent reproductive efficiency.

• Breed Differences: Some breeds are naturally more fertile or mature earlier than others.
• Heritability of Fertility Traits: Fertility is a moderately heritable trait. Selecting replacement heifers from dams with good reproductive records and using bulls from fertile lines can improve herd fertility over time.

Age and Parity: Lifecycle Considerations

A cow’s age and how many calves she has had (parity) also influence her reproductive performance.

• Heifers vs. Mature Cows: Heifers need to reach a certain size and weight before puberty and breeding. First-calf heifers often have longer postpartum anestrus periods because they are still growing while also lactating and recovering from their first calving.
• Older Cows: Very old cows may experience a decline in fertility as their reproductive systems age.

By actively managing these factors – providing optimal nutrition, maintaining herd health, minimizing stress, and making informed genetic selections – you can create an environment that supports robust heat cycles and maximizes fertility in your cattle.

Effective Heat Detection Methods

Accurate and consistent heat detection is the cornerstone of a successful breeding program. Relying solely on visual observation can be challenging, especially in large herds or extensive grazing systems. Combining visual checks with various heat detection aids can significantly improve your accuracy and efficiency.

Visual Observation: The Traditional Method

Visual observation remains a primary method, but its effectiveness depends heavily on the observer’s skill, dedication, and the frequency of checks.

• Frequency and Duration of Observation Periods:
  • For optimal results, observe cows for at least 20-30 minutes, two to three times a day.
  • Crucially, observe during quiet times when cows are most active and likely to display heat signs:
    • Early Morning: Just before or at sunrise (e.g., 5:00 AM – 7:00 AM).
    • Late Evening: Just before or at sunset (e.g., 5:00 PM – 7:00 PM).
    • These times often coincide with cooler temperatures and reduced human activity, allowing cows to express natural behaviors.
  • An additional midday check can be beneficial, especially during cooler weather.
• Importance of Quiet Environment: Disturbing cows during observation can suppress heat behavior. Approach quietly, avoid sudden movements, and allow them to interact naturally.
• Who Should Observe?: Ideally, the same person or a small, well-trained team should be responsible for heat detection to ensure consistency in recognizing subtle signs.

Heat Detection Aids: Boosting Your Accuracy

Technology and simple tools can greatly enhance your ability to detect heat, particularly for silent heats or when visual observation time is limited.

• Tail Paint/Crayon/Chalk:
  • How it works: A strip of paint, crayon, or chalk is applied along the tail head and backbone. When a cow is mounted, the paint/crayon is rubbed off or smudged.
  • Advantages: Inexpensive, easy to apply, provides a clear visual indicator of mounting activity.
  • Limitations: Can be rubbed off by fences, trees, or other non-mounting activities; requires regular reapplication.
• Kamar Heatmount Detectors/Estrotect Patches:
  • How it works: These are pressure-activated patches glued to the tail head. Kamar detectors contain a capsule that bursts and releases a colored dye when sufficient pressure (from a mount) is applied. Estrotect patches have a rub-off surface that changes color when activated by mounting.
  • Advantages: More accurate than tail paint for detecting true mounts; provides a permanent record of mounting.
  • Limitations: Can be dislodged; false positives can occur from rubbing on objects or other cows not in heat; requires proper application.
• Pedometers/Activity Monitors (e.g., AfiMilk, SCR, CowManager):
  • How it works: Electronic sensors (worn on the leg, neck, or ear) continuously monitor a cow’s activity levels. Cows in heat typically show a significant increase in walking, standing, and overall activity. The data is transmitted to a computer or smartphone, alerting the farmer to potential heats.
  • Advantages: Highly accurate, continuous monitoring, reduces labor, provides precise timing of increased activity, can detect subtle heats.
  • Limitations: High initial investment cost; requires a robust software system and internet connectivity.
• Androgenized Animals (Teaser Bulls/Gomers):
  • How it works: A vasectomized bull (unable to impregnate but still expresses libido) or a steer treated with testosterone is used to identify cows in heat. These “teaser” animals will attempt to mount cows in estrus. Often, they are fitted with chin-ball markers that leave a paint mark on the back of mounted cows.
  • Advantages: Highly effective, natural detection, can cover large areas.
  • Limitations: Requires management of teaser animals; potential for injury to cows or teaser; some risk of disease transmission if not properly managed.
• Crayon/Chalk: Similar to tail paint, but often less durable.
• Vaginal Probes/Temperature Monitors: Less common for daily heat detection but exist. Vaginal probes measure electrical resistance, which changes during estrus. Internal temperature monitors can detect slight temperature increases associated with estrus.

Here’s a comparison of common heat detection methods:

Method	Description	Pros	Cons	Ideal Use Case
Visual Observation	Directly observing cows for primary and secondary heat signs.	Inexpensive, simple to implement.	Labor-intensive, requires trained observer, easily missed heats, observer fatigue.	Small herds, dedicated staff, during quiet periods.
Tail Paint/Crayon	Applying paint/crayon to tail head; rubbed off by mounting.	Very low cost, easy to apply, quick visual cue.	Can be rubbed off by non-mounting activity, needs reapplication, less precise.	Any herd size as a primary or secondary aid.
Kamar/Estrotect Patches	Pressure-activated patch glued to tail head; changes color or bursts.	More accurate than paint for true mounts, clear indicator.	Higher cost than paint, can be dislodged, requires careful application.	Medium to large herds, where precise mount detection is critical.
Activity Monitors (Pedometers)	Electronic sensors track increased cow movement.	Highly accurate, continuous, labor-saving, detects subtle heats, provides timing data.	High initial investment, requires tech infrastructure, maintenance.	Large commercial dairies/beef operations, high-value animals.
Teaser Bulls (Vasectomized)	Sterile bull identifies cows in heat, often with chin-ball marker.	Highly effective, natural behavior, covers large areas.	Requires managing a bull, potential for injury, risk of disease if not truly sterile.	Large, extensive beef operations, where labor for visual observation is limited.

The best approach often involves a combination of methods. For example, consistent visual observation complemented by tail paint or activity monitors can provide a highly accurate and efficient heat detection program for your farm.

Record Keeping: Your Breeding Program’s Backbone

Excellent record keeping is not just good practice; it’s an indispensable tool for managing a successful breeding program. Without accurate records, you’re essentially operating blind, unable to identify trends, troubleshoot issues, or make informed decisions.

What to Record

For each individual cow in your breeding herd, aim to record the following key pieces of information:

• Cow ID: Unique identifier for each animal.
• Date of Birth: Helps track age and maturity.
• Calving Date: The date she last calved. This is crucial for calculating postpartum intervals and predicting when she should resume cycling.
• Date(s) of Heat Observation: Every time you observe a cow in heat, record the date and time. Note the intensity of heat signs (e.g., “strong standing heat,” “light activity”).
• Breeding Date(s): The exact date and time of breeding.
• Service Sire (Bull Used): If using AI, record the specific bull’s ID (e.g., “A.I. Sire 123”). If using natural service, record the herd bull’s ID.
• Breeding Method: AI (Artificial Insemination) or NS (Natural Service).
• Pregnancy Diagnosis Date and Result: Date of preg-check and whether she was confirmed pregnant (PD+) or open (PD-).
• Expected Calving Date (ECD): Calculate this based on the breeding date (gestation period is approximately 283 days).
• Notes/Observations: Any unusual behavior, health issues, treatments, or specific observations related to her heat or breeding.

Benefits of Good Records

Comprehensive and well-maintained records provide invaluable insights and enable proactive management:

• Predicting Next Heat: Knowing a cow’s last heat date allows you to predict her next expected heat (approximately 21 days later), enabling focused observation.
• Identifying Problem Cows: Records highlight cows that are not cycling, have long postpartum anestrus periods, or repeatedly fail to conceive. This allows for early intervention, veterinary consultation, or culling decisions.
• Evaluating Bull Performance: If using natural service, records help assess which bulls are siring pregnancies effectively and which might be subfertile.
• Monitoring Calving Interval: Records allow you to track the average calving interval for your herd and for individual cows, a key metric for reproductive efficiency.
• Optimizing Breeding Season: Historical data can inform decisions about breeding season length, bull power, and synchronization programs.
• Economic Analysis: Good records are essential for calculating reproductive key performance indicators (KPIs) and understanding the economic impact of your breeding program.

Simple Methods vs. Software

The method of record keeping can vary based on herd size and preference:

• Simple Methods (Notebooks, Calendars, Whiteboards):
  • Pros: Low cost, easy to start.
  • Cons: Can be difficult to analyze large amounts of data, prone to errors, not easily shared or backed up. Best for very small herds.
• Spreadsheets (Excel, Google Sheets):
  • Pros: More organized than notebooks, allows for basic sorting and filtering, customizable.
  • Cons: Still requires manual data entry and formula creation, can become complex for larger herds.
• Dedicated Herd Management Software (e.g., HerdPoint, PC Dart, BoviSync, CowSense):
  • Pros: Designed specifically for livestock records, automates calculations (e.g., ECD, calving interval), generates reports, allows for data analysis, often cloud-based for accessibility and backup.
  • Cons: Higher initial cost, learning curve, requires consistent data entry.

Regardless of the method, the most important aspect is consistency and accuracy. Make record keeping a daily habit, and ensure the information is readily accessible when needed. This dedication will pay dividends in the long-term productivity and profitability of your herd.

Troubleshooting Common Heat Cycle Issues

Even with diligent observation and good management, you may encounter cows that don’t seem to follow the textbook heat cycle. Understanding common issues and their causes can help you address them effectively.

Silent Heats (Subestrus): The Hidden Challenge

A silent heat, or subestrus, occurs when a cow ovulates and has a normal physiological cycle but does not display obvious external signs of heat. This is a significant challenge for heat detection and can lead to missed breeding opportunities.

• Causes:
  • Nutrition: Most commonly, silent heats are linked to cows in a negative energy balance or with inadequate body condition (thin cows). Their bodies prioritize survival and milk production over displaying overt reproductive behaviors.
  • Stress: Environmental stressors (heat stress, overcrowding), social stress (bullying by dominant cows), or handling stress can suppress the behavioral signs of estrus.
  • Post-Calving: Early in the postpartum period, cows may have their first ovulation without showing strong heat signs as their bodies are still recovering and hormones are fluctuating.
  • Genetics: Some cows may be genetically predisposed to weaker heat expression.
  • Disease: Subclinical infections or metabolic diseases can also contribute.
• Detection Strategies:
  • Increased Observation: More frequent and longer observation periods, especially during quiet times, can help catch subtle signs.
  • Heat Detection Aids: Activity monitors (pedometers) are excellent for detecting silent heats as they track physiological changes in movement regardless of visible behavior. Tail paint or patches can also indicate mounting activity even if the cow doesn’t stand perfectly still.
  • Teaser Animals: Vasectomized bulls or androgenized cows are very effective at identifying cows in silent heat.
  • Synchronization Protocols: Estrus synchronization programs can be used to induce or group heats, making breeding possible even without strong heat signs (e.g., fixed-time AI).

Anestrus (No Heat): When Cycles Stop or Don’t Start

Anestrus is the complete absence of heat cycles. This means the cow is not ovulating and therefore cannot become pregnant. It’s a major cause of reproductive inefficiency.

• Causes:
  • Low Body Condition Score (BCS): This is the most common cause. Cows that are too thin after calving (or heifers that are underweight) simply do not have enough energy reserves to initiate or sustain a reproductive cycle.
  • Retained Placenta/Uterine Infections: If the uterus is not healthy and fully involuted after calving, it will prevent the cow from cycling. Metritis and endometritis are common culprits.
  • Cystic Ovaries: Ovarian cysts can disrupt normal hormonal patterns, leading to persistent anestrus or irregular cycles.
  • Persistent Corpus Luteum (CL): Sometimes the CL (which produces progesterone) doesn’t regress as it should, preventing a new cycle from starting. This can happen after an early embryonic death or if the cow is actually pregnant but the pregnancy was missed.
  • Nutritional Deficiencies: Specific mineral (e.g., phosphorus) or vitamin deficiencies can lead to anestrus.
  • Stress/Disease: Chronic stress or underlying illness can suppress reproductive function.