Q: We have a 19-year-old broodmare that bagged up and developed edema (fluid swelling) on her belly starting nearly six weeks before her due date. Her prospective due date is June 1, but really could go anywhere from May 15 to June 1. Her breeding dates were June 19 and 20, 2011. She bagged up on April 9. What could this be a sign of? —Marni Hoffman, via email

A:The condition your mare displays is a common one. The first thing we need to do is differentiate the edema (that you described correctly in your question) from the filling in the udder that is characteristic of impending foaling (parturition). In the majority of cases edema associated with late gestation is of no concern, but premature filling of the udder with milk is.

The udder fills with milk up to two to four weeks prior to foaling. A waxy secretion appears on the teat 24 to 48 hours before foaling that is usually an accumulation of colostrum and the plug it makes in the teat orifice. The most common causes of an udder filling with milk prematurely are twins (since mares with twins rarely gestate full term), fetal compromise (sometimes from herpesvirus infection), or fetuses with twisted umbilical cords. In maiden mares (those that have never foaled before) preparturient udder filling might not occur, and in many of these mares the udder doesn’t fill until foaling or shortly thereafter.

Another common cause of udder filling and premature parturition is placentitis (inflammation of the placenta), which is sometimes associated with vaginal discharge. Your veterinarian can evaluate the