A small percentage of broodmares will be afflicted with urine pooling, also known as vesicovaginal reflux (VVR) or urovagina. But when it does occur, it is a serious problem that sometimes can only be remedied with surgery. Simply put, urine pooling occurs when urine refluxes forward in the vagina and against the cervix instead of being flushed to the rear and evacuated through the vulva. The problem is at its most severe when the mare is in estrus because then the cervix is relaxed and the urine may enter the uterus, irritating and contaminating it.

Urine in the cranial (forward) portion of the reproductive tract as well as in the uterus itself produces chemical irritation, plus spermicidal activity. The irritation it causes can provide a breeding ground for harmful bacteria.

Older mares which have delivered a number of foals are more at risk than their younger counterparts, says Gayle Trotter, DVM, a surgeon at Colorado State University who has written textbook literature on the problem and the surgical procedures involved in correcting it.

When the problem occurs in younger mares, says K. Jack Easley, DVM, MS, of Shelbyville, Ky., and also the author of textbook literature on VVR, it could mean urine pooling with added complications. The young mare might have an ectopic ureter–displacement of the tube that conveys urine from the kidney to the bladder–and, as a result, might empty urine into any area along the reproductive tract. This is a problem that can only be solved with surgery