Tips, Tricks and Techniques – Fetal Sex Determination

By Dr. Andrew Bronson, DVM | Created on Thu Nov 2, 2017

Fetal gender determination can be a large value-added feature for those utilizing ultrasound technology. To accurately determine the gender of the fetus, most experts do not recommend attempting to fetal sex earlier than day 57. The optimal window when using a linear probe ultrasound such as the BoviScan HD, is between day 57 and 80 days.  When using a convex rectal probe ultrasound (ReproScan XTC and BoviScan Curve), Dr. Andrew Bronson recommends waiting until day 70 to begin fetal sexing. The upper limit for age of fetus when using the convex rectal probe is determined by size of cow and other factors. Fetal gender has been successfully determined in cattle up to 120 days pregnant if the cows are small and conditions are right. Therefore, the window of opportunity for gathering gender data varies depending upon the ultrasound probe type, size of cows, consistency of manure, facilities and sunlight. If conditions are favorable, fetal gender can be determined much easier than in challenging conditions. If you are new to fetal gender determination, practice on cows that are 60 to 75 days with a linear probe unit or 75 to 90 days pregnant with a convex rectal probe unit.

At about day 80 the GT (genital tubercle) becomes more skin covered which causes it to lose its echogenicity. Before this time, the GT is very echogenic making it easier to spot with an ultrasound.  After 80 days, the larger scanning area provided by convex probes makes it easier to find the male or female GT or the males scrotum.   

To determine gender, it is recommended that you look for a male GT first. To positively identify a bull, begin by locating the umbilicus and looking for the male GT directly behind it. To determine a heifer calf you deduce that the GT is not near the umbilicus and then move caudally to look under the tail for a female GT. In more advanced pregnancies (80 to 120 days), male fetuses are often identified by the scrotum. The scrotum is much easier to find when the fetus is backwards which happens regularly in this age category. Females are more difficult to positively identify as the tail often covers the female GT (vulva in 80 to 120 day fetuses).

Determining fetal sex can be quite challenging, and becoming accurate requires a considerable amount of practice. ReproScan works with Dr. Craig DeMuth to offer intensive courses that cover fetal sex determination. If you are interested in the courses please see our training page or contact Elle for 2018 dates.