In a recent article, we discussed how heat stress can affect fertility in both cows and bulls. While the effects of summer heat cannot be reversed, producers now have an opportunity to evaluate its impact through pregnancy diagnosis. This year's pregnancy check may reveal more than simply which cows are pregnant and which are open. It can provide valuable insight into breeding season performance, the extent of heat-related reproductive losses, and opportunities for herd improvement.
Heat stress can reduce embryo survival, lower conception rates, and temporarily impair bull fertility. As a result, some producers may observe higher-than-expected numbers of open cows or a larger proportion of pregnancies occurring later in the breeding season. Understanding when pregnancies occurred is particularly important in herds that used fixed-time artificial insemination (FTAI) followed by natural service. Determining whether a pregnancy resulted from AI or from cleanup bulls helps evaluate synchronization success, bull performance, and overall reproductive efficiency.
Pregnancy diagnosis is more than a reproductive checkpoint. It is a management tool that helps producers assess breeding outcomes, identify nonpregnant females, and make timely culling and feeding decisions before winter. The best diagnostic method depends on herd goals, labor availability, timing, and the level of information desired.
Common Pregnancy Diagnosis Methods
The two most common methods used in beef cattle are transrectal palpation and transrectal ultrasound.
- Transrectal palpation remains the most widely used method because it is inexpensive, fast, and readily available. Experienced practitioners can identify pregnancy by detecting uterine fluid, membrane slip, or placentomes in later gestation. However, palpation primarily provides a pregnant-or-open diagnosis and is less reliable for accurately determining fetal age.
- Transrectal ultrasound allows direct visualization of the embryo and can detect pregnancy as early as 25 days after breeding. Ultrasound can confirm fetal viability through detection of a heartbeat, estimate fetal age, and determine fetal sex later in gestation. Although it requires specialized equipment and training, ultrasound provides significantly more information than palpation and is particularly valuable when distinguishing AI from natural-service pregnancies.
Differentiating AI and Bull-Bred Pregnancies
Many producers turn cleanup bulls out approximately two weeks after FTAI to breed females that fail to conceive to AI. While this approach maximizes overall pregnancy rates and minimizes handling, it can complicate efforts to determine breeding dates.
Because AI and natural-service pregnancies may differ in age by only 10 to 14 days, differentiating them using palpation alone can be difficult. Research has reported error rates ranging from approximately 6% to 7% when estimating fetal age by palpation alone. Ultrasound offers a significant advantage because fetal measurements, particularly crown-rump length, are strongly associated with embryo age and can improve pregnancy-age accuracy.
For producers evaluating synchronization programs, identifying whether pregnancies resulted from AI or natural service provides valuable information regarding conception rates and program success.
Ultrasound Versus Palpation
A common misconception is that ultrasound is too slow for commercial beef operations. In reality, ultrasound can be performed efficiently by trained technicians. Studies have shown that palpation requires only slightly less time per cow than ultrasound (11.3 seconds, compared to 16.1 seconds), and experienced palpators generally transition quickly to ultrasound technology.
While both methods can accurately identify pregnancies, ultrasound offers additional benefits, including:
- Fetal aging
- Fetal viability assessment
- Identification of AI versus bull-bred pregnancies
- Fetal sex determination
- Improved diagnostic precision for less experienced practitioners
The greatest value of any pregnancy diagnosis program, however, comes from having a management plan in place for open cows once they are identified.
Concerns About Pregnancy Loss
Producers occasionally express concern about pregnancy loss caused by early transrectal palpation. Research has produced mixed results, with some studies reporting a slight increase in pregnancy loss and others finding little or no effect. Regardless of the technique used, factors such as nutrition, body condition, stress, disease, and overall herd health generally have a much greater impact on pregnancy maintenance and calving rates than the diagnostic procedure itself.
Timing Matters
Accuracy of pregnancy diagnosis depends heavily on timing. Ultrasound accuracy is lower before 24 days of gestation but improves substantially as pregnancy progresses. After approximately 25 to 26 days of gestation, visualization of the embryonic vesicle and embryo becomes much more reliable. For practical herd management, waiting until pregnancies are at least 28-30 days old helps minimize false diagnoses and improves confidence in the results.
Fetal Sexing
An additional advantage of ultrasound is the ability to determine fetal sex between approximately 55 and 110 days of gestation. During this period, the location of the genital tubercle can be used to distinguish male and female fetuses. While not necessary for all operations, fetal sexing can provide valuable information for producers using sexed semen, retaining replacement females, or targeting specific marketing strategies.
Conclusion
Following a summer marked by heat stress, pregnancy diagnosis offers producers an opportunity to measure the true reproductive impact within their herds. Beyond identifying pregnant and open females, pregnancy checks can reveal breeding season patterns, evaluate synchronization success, assess bull performance, and guide management decisions before winter. For some operations, palpation may provide all the information needed. For others, particularly herds that utilize AI, ultrasound offers significant advantages through fetal aging, viability assessment, and differentiation of AI and natural-service pregnancies. Regardless of the method chosen, pregnancy diagnosis remains one of the most valuable tools available for improving reproductive efficiency and overall herd profitability. Extension specialists can support producers by offering training in palpation and ultrasound techniques, interpreting test results, and integrating pregnancy diagnosis into broader reproductive management plans.
