Pneumovagina.

Pneumovagina.
Poor muscle tone of the labia lead to parting of the lips and aspiration of air into the vagina. This condition is more commonly seen in older and thin mares but may be found even in young thin nulliparous mares. Pneumovagina is more common at the time of estrus. The ballooned vagina may readily be palpated per rectum.

Drost M (1971)