Fetal Sexing

Bovine Division

Wouldn’t it be nice to know the gender of calves before they were even born? With fetal sexing, it is possible to determine if a calf is a bull or heifer while it is still in utero. Fetal sexing is a non-invasive procedure that uses transrectal ultrasonography on a pregnant cow or heifer to determine the gender of the calf (or calves) she is carrying.

Understanding the Fetal Sexing Process

With a gloved arm, the technician gently guides an ultrasound probe into the rectum of the restrained cow. The probe is positioned on the floor of the rectal wall and manipulated until a clear image of the fetus is obtained. The main body parts (head, trunk, limbs, etc.) are first visualized to determine the fetus’s orientation. The technician then scans the near the umbilical cord and under the tail to locate the highly echogenic genital tubercle (GT).

The GT is a structure present in both the developing male and female fetus that ultimately gives rise to either the penis (male) or the clitoris (female). The presence of a GT directly behind the umbilicus indicates a bull calf, while a GT located under the tail is indicative of a heifer calf. Depending on the stage of gestation, the technician may also seek to visualize scrotal swellings or mammary teats to assist in determining the calf’s gender.

Advantages of Fetal Sexing

Marketability of bred cows

Some producers have a greater incentive to produce either heifer or bull calves. For example, the market for heifer calves is typically much more robust than bull calves in the dairy industry whereas bull calves may hold more value than heifer calves for a commercial beef producer. Therefore, when bred females are sold, their value in a specific market may be greatly increased when the sex of the fetus is known.


For cows carrying twins, fetal sexing can be used to determine whether the twins are of the same gender or whether a freemartin heifer is likely. When a heifer is twinborn with a bull, she is typically rendered infertile due to masculinization by male hormones through a shared blood supply in utero. By knowing the genders of the developing twins, a producer knows whether or not to expect a freemartin and can make management decisions accordingly.


Knowing how many bull and heifer calves to expect at calving can help producers get a jump-start on future plans. A producer who retains his own breeding females can get an idea of whether or not he needs to budget for purchasing additional replacements. For the cattleman marketing bulls, he can begin negotiating and filling bull contracts earlier. When a purebred breeder sells a flush guaranteeing a minimum number of pregnancies of a specific gender, fetal sexing the calves carried by recipients will let her know whether the agreement has been fulfilled or if the donor needs to be flushed again.

Important Considerations for Fetal Sexing


Although fetal sexing can provide valuable information to cattle producers, there is a limited window of time in which it can be conducted. Since the GT begins its migration around day 50 of pregnancy, it is not possible to distinguish bull calves from heifers by ultrasound before then. The earliest that fetal sexing can be conducted with any degree of accuracy is 55 days, although many technicians advocate waiting until the GT completes its migration around day 60 of gestation. On the other end of the spectrum, fetal sexing generally needs to be completed by 90 days of gestation. Beyond this point, the fetus is often too deep within the abdominal cavity to reach with the ultrasound probe or is too large for a satisfactory image to be obtained. Although fetal sexing is possible beyond 90 days, it is a gamble whether or not the gender will be able to be determined.


The accuracy of fetal sexing is primarily attributed to the timeframe in which it is conducted as well as the skill and confidence of the technician. When conducted between 60 and 90 days of gestation by a proficient technician, fetal sexing accuracy should be at least 95%.


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