Your veterinarian can examine the heifer at 3 to 6 months of age to see if the female tract is developing (some use a test tube to conduct the test). Vaginal length for normal heifers are usally 14 centimeters (5.5 inches) or greater. Freemartin vaginal length are typically 7 to 11 cm (2.8 to 4.3 inches). There are also blood tests that can tell you if a heifer is a freemartin.
Mike Hutjens, Extension Dairy Specialist, U of IL – Illini DairyNET
Hugh Chester-Jones, U of MN dairy and beef specialist.