You notice a sucking sound coming from a mare's rear end when she moves. The most common cause of this is air being sucked into the vagina during movement.

This is common where vulvar or vaginal injury or poor conformation has caused loss of the vulvar seal. Some mares moving at high speed or extra exertion will suck air even through a normal vulvar seal. This is due to huge changes in intra-abdominal pressures during exercise at speed. This is the logic behind performing Caslick's procedures on racehorse mares. Mares with neurologic injury affecting the function of the pelvic and vaginal muscles will also "wind suck", as will mares that have had repeated Caslick's procedures.

This observation occurs when there is a loss of normal vulvar function. The primary consequence relates to reproductive health. In most cases, it does not affect health otherwise.