Bovine Pregnancy Determination
With input costs continually on the rise, cattle raisers must be diligent about managing their expenditures. As the annual cost to keep a cow approaches $900, one of the biggest liabilities in today’s cattle industry is the open cow. Identifying open cows to facilitate culling decisions is a good tactic to limit the impact these cows have on the bottom line.
Understanding the Pregnancy Determination Process
The general purpose of pregnancy checking cows is to distinguish between open and pregnant females. The most widely used methods in the beef industry are rectal palpation and ultrasonography although other methods, such as blood and milk tests, do exist.
The technician inserts a gloved arm into the rectum of a restrained cow and palpates downward through the rectal wall to locate and identify the structures of the reproductive tract. Although the most definitive indication of an existing pregnancy is direct palpation of the fetus or fetal membranes, the technician must sometimes rely on other indicators when the fetus cannot be palpated. The size, location and tone of the uterine horns as well as the presence of placentomes (button-like structures that are the point of attachment of the placenta to the uterus) can provide clues as to whether or not the cow is pregnant.
Transrectal ultrasonography can also be utilized to detect pregnancy in cattle. The technician inserts a gloved arm holding an ultrasound transducer into the rectum of a restrained cow. The transducer uses sound waves to generate echogenic images of the internal structures of the cow. The technician manipulates the transducer so that the reproductive tract can be visualized on the ultrasound screen. Images of the uterus are examined to identify the presence or absence of the amniotic sac and/or fetus.
Advantages of Determining Pregnancy
Identify open cows: Arguably, the most important benefit of diagnosing pregnancy in cattle is to identify non-pregnant cows. Open cows are a significant economic liability, but identifying these cows as early as possible allows producers to make timely culling decisions. Timely culling of open cows limits the cost associated with maintaining nonproductive cows and also allows producers to capitalize on a stronger market before the seasonal decline in cull cow prices. Open cows can be identified as early as 35-40 days after breeding with rectal palpation while ultrasonography can be utilized to detect pregnancies even earlier at 28 days of gestation.
Quick and inexpensive: Rectal palpation is a quick and inexpensive method for identifying nonpregnant cows. It provides immediate results and allows producers to sort off open cows as they exit the chute. Although pregnancy diagnosis by ultrasonography is typically slightly more expensive than rectal palpation, it still provides producers with instantaneous results.
Identify AI- vs bull-bred cows: For operations using both artificial insemination (AI) and bulls to breed cows, it can sometimes be difficult to determine if a calf is sired by the AI bull or by the service bull. Pregnancy determination early in gestation can be utilized to determine if a cow was AI- or bull- bred. One caveat is that there must be a delay of about two weeks from the last AI until the cows are exposed to bulls in order for the technician to be able to tell whether the cow conceived by AI or natural mating.
Estimate calving date: Many producers like to know when they can expect cows to calve. Depending on when the pregnancy determination is made, the gestational stage may also be approximated. By knowing the approximate number of days or months pregnant, producers can estimate when cows should calve and manage them appropriately.
Additional information: Ultrasonography can also provide additional information beyond what is typically provided by other methods of pregnancy diagnosis. Viability of the pregnancy can be determined using ultrasonography. The fetal heartbeat can be observed by ultrasound and a skilled technician can identify signs of an aborting pregnancy. Ultrasonography can also reveal the presence of twins and identify the gender of the developing fetus (or fetuses) during a specific gestational window.
Monitor herd status: Pregnancy checking cows can also help monitor the overall health of a herd. An uptick in the percentage of open cows may be indicative of a problem. Trichomoniasis, bovine viral diarrhea (BVD), neosporosis and other diseases often cause cows to abort. Nutritional deficiencies can also produce higher-than-normal percentages of open cows as cows lacking adequate nutrition may fail to conceive or maintain a pregnancy. Pregnancy determination can also reveal subfertile bulls or a problem in an AI program. Early identification of these issues allows producers to tackle the problems as quickly as possible.
Important Considerations for Determining Pregnancy
Accuracy is critical: As culling decisions are often based at least in part on pregnancy status, it is imperative that the accuracy of the pregnancy diagnosis be spot-on. Otherwise, a pregnant cow could be inadvertently culled or an open cow could remain in the herd. Admittedly, some cows may be too early in gestation for the pregnancy to be detected. This can be alleviated by waiting to check cows until at least 28 days (for ultrasound) or 35-40 days (for rectal palpation) since the last possible breeding. Any questionable cows can also be reexamined at a later date to ensure accuracy.
Early embryonic mortality: An estimated 10-15% of embryonic loss occurs between day 17 and 42 of pregnancy. Therefore, it is reasonable to expect that a percentage of cows who are diagnosed as pregnant within this timeframe will ultimately lose their pregnancy. If this is of high concern, cattle can wait to be checked until after this period has passed. If early detection is imperative, cows can be rechecked at a later date to ensure the pregnancy is being sustained.
Limited timeframe for accuracy: Although rectal palpation can be used to identify a pregnancy from around 35 days until the day of parturition, the accuracy with which the number of days pregnant can be estimated declines as gestation progresses. Generally speaking, a trained technician should be able to give a close estimate on the number of days pregnant up to about 120 days of gestation. Beyond this, the weight of the fetus pulls the reproductive tract down into the abdominal cavity of the cow and out of reach of the technician. An estimate of days pregnant at this point is likely to be less precise. Rather, a more generalized approximation such as “4 months bred” or “period 2” is warranted. Similarly, the use of ultrasound is generally limited to the first 120 days of pregnancy before the fetus is too large to be viewed on the screen. When used for fetal sexing, ultrasound use is limited to around 60-90 days of gestation. Fetal sex can sometimes be determined after 90 days but is highly dependent on the location of the reproductive tract in the abdominal cavity and the position of the fetus within the tract.
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