Anterior vaginal and intrauterine pressures in mares

Resting pressure in the anterior vagina and uterus was measured monthly in eight mares for 5 mo. During this time, four of the mares maintained their body weight and four lost weight. Mean anterior vaginal pressure was -11.9 mmHg, and intrauterine pressure was -5.3 mmHg; the latter was positively correlated to body weight and weight/height ratio. Anterior vaginal pressure and uterine pressure were also positively correlated. Allowing air into the anterior vagina raised this pressure to -4.0 mmHg, i.e. higher than uterine pressure. There was a tendency for genital tract pressures to be lower in anoestrous mares than those which remained cyclic. Some physiological events caused marked increases in genital pressures.