Determining sex of the bovine fetus by ultrasonic assessment of the relative location of the genital tubercle

Abstract

The objectives were to characterize the ultrasonic morphology and location of the genital tubercle (forerunner of penis and clitoris) in cattle fetuses and to determine whether assessment of the relative location of the tubercle is useful for predicting fetal sex. Daily ultrasound examinations were done on Days 48 to 60, sex was diagnosed, and the degree of certainty of the diagnosis was scored (1 = not determinable; 2, 3 and 4 = determined with minimal, intermediate, and maximal certainty, respectively). The fetuses were recovered by induced abortion on Day 60 and sex determined by gross inspection of the external genitalia. In both sexes, the genital tubercle was a hyperechogenic bilobar structure and each lobe was elongated and oval shaped, enabling it to be recognized by ultrasound. On the first day that the certainty level for diagnosis of sex reached its highest value per heifer, sex was correctly diagnosed in 16 of 16 heifers (confidence interval for correct diagnosis, 83 to 100%). The mean certainty level increased from 1.2 ± 0.2 on Day 48 to 4.0 ± 0.0 on Day 58. The tubercle was located between the hind limbs on Days 48 and 49 and then moved toward the umbilical cord in males and toward the tail in females. In males, the tubercle was immediately caudal to the umbilical cord on mean Day 56.0 ± 0.8 and in females was under the tail on mean Day 53.8 ± 0.2. In conclusion, ultrasonic identification and estimation of the relative location of the genital tubercle by an experienced operator was a reliable technique for determining sex of the bovine fetus beginning on Day 55 and extending through the last day of the experiment (Day 60).