| Abstract: | Determining sex of the equine fetus by transrectal ultrasonic assessment of the relative location of the genital tubercle (forerunner of penis and clitoris) was studied in 23 mares. Ultrasound examinations were done every other day on Days 35 to 97 or until the fetus was manually removed for comparative diagnosis of sex by gross inspection. In both sexes, the genital tubercle was a hyperechogenic bilobulated structure 2 mm in diameter when first identifiable between Days 40 and 54. Initially, the tubercle was located between the hind limbs and sex was not diagnosable. By a mean of Day 63, the tubercle was immediately caudal to the umbilical cord in males and under the tail in females. The optimal time for sex diagnosis was Days 59 to 68. During this time, the tubercle was readily accessible and assignable to a location characteristic of its sex, and sex was correctly diagnosed for all examinations of all fetuses except for 2 errors in the first mare used in the study. Between Days 69 and 97 all attempted diagnoses were correct, but a diagnosis was not attempted in 13% of the examinations because of difficulty in obtaining an adequate view in some mares. Although the technique was highly accurate for diagnosis of fetal sex, it is emphasized that the operator was experienced and the examining conditions were optimal. |
