ABSTRACT
There are three main anatomical barriers that maintain the integrity of the caudal reproductive tract: the vulva including its labia, constrictor muscles and perineal body; the vestibular sphincter including the constrictor muscles of the vestibule; and the cervix. These barriers block the aspiration of air and contaminants into the reproductive tract. Ultrasound waves of the type commonly used are not hazardous and ultrasonographic examination of the reproductive tract increases the quality and accuracy of information. Recipient mares should be healthy, free from any reproductive problems of their own, cycling normally and preferably young. Direct vaginal examination and viewing of the cervix is no longer considered a safe way of confirming pregnancy as it risks introducing bacteria into the internal reproductive tract or causing inflammation, both of which can lead to prostaglandin release, luteolysis and pregnancy failure. The vulva and vestibule act as the first barrier between the reproductive tract and the environment.
