Transabdominal ultrasonographic determination of fetal gender in the horse during mid-gestation.

This research delves into the use of transabdominal ultrasonography to determine the gender of horse fetuses during mid-gestation. The study found the process to be highly accurate when performed between 100 to 220 days of gestation.

Study Design and Participants

• In this study, gender determination of the equine fetus using transabdominal ultrasonography was tested in 20 mares.
• These mares were split into two groups: one group of 10 research mares that were regularly scanned every two weeks from 100 days gestation until birth, and a client group of 10 mares that only underwent ultrasonography once during mid-gestation.

Observations

• In male fetuses, the investigators observed the penis and/or prepuce on 71 separate occasions between 102 and 258 days gestation.
• The external genitalia of male fetuses showed a round shape with echogenic foci up to around 140 days gestation, after which it appeared triangular.
• The researchers noted the testes to be oval-shaped and homogeneously appearing in ultrasonographic images.
• Females were identified on the basis of the presence of mammary glands and teats. They found them on 23 occasions between 118 and 227 days gestation.
• The researchers noticed a characteristic circular echo from the homogeneous appearing fetal ovaries between 100 to 134 days gestation.

Accuracy of the Procedure

• All gender identification (n = 98) based on the above male and female anatomical features were accurate, as they matched the gender of the foals at birth.
• While the majority of the gender determinations were made through a transabdominal approach (87 out of 98), the investigators also found the transrectal approach useful when foals were in posterior presentation or located higher in the mares’ abdomen.

Timing and Equipment

• The best time span for this ultrasonographic procedure (for both sexes) was between 100 and 220 days gestation, after which it was increasingly challenging to recognize the required anatomical structures.
• For this procedure, good quality diagnostic scanners typically used in equine reproduction with a 5.0 MHz probe can be employed for up to 160 days gestation. However, a 3.5 MHz transducer may be needed beyond that period due to the increasing size of the fetus.