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 combined thickness of the uterus and placenta (CTUP measurement) to determine if the placenta and/or foal are compromised. Veterinarians can treat this condition.

Edema of the udder (which you see here) and of the ventral (underside of the abdomen) midline often occurs in late pregnancy and is normal. It usually indicates vascular system compromise because of the size of the fetus and its positioning. The fetus might move to occlude the normal return of blood to the heart by compressing the caudal vena cava (one of the vessels through which all of the body's oxygen-depleted blood flows). This type of edema is associated with advancing pregnancy, reduced willingness to exercise, and/or confinement.

Ventral edema associated with limb edema can be related to pathological conditions such as purpura hemorrhagica, which is an autoimmune response to past Streptococcus equi (strangles) infection. Larger swellings associated with defects in the body wall can be related to prepubic tendon (the ligament that supports the abdomen) rupture. In these cases the ventral body wall's integrity is compromised.

Another common question is if ventral edema and udder edema/filling can be associated with fescue toxicity. Mares exposed to fescue in the last 90 days of gestation that experience subsequent fescue toxicosis display prolonged (not shorter) gestation and agalactia, or deficient milk production (in contrast with premature udder filling).

In conclusion, the clinical signs you see in your mare are normal for an older mare and indicate positional changes of a large fetus that is inhibiting the mare’s normal blood circulation pattern. The mare is moving less, and the abdominal cavity is reaching its capacity. When the mare foals, the circulatory system will return to normal and the edema will resolve without any further treatment.

About the Author

Benjamin Espy, DVM, Dipl. ACT

Benjamin Espy, DVM, Dipl. ACT (boarded in equine reproduction), has practiced veterinary medicine in Texas and Kentucky. He has been licensed to practice acupuncture for nine years and is on numerous AAEP committees and task forces. Espy serves on the alternative therapy committee for the Texas Veterinary Medical Association, and he's an animal treatment consultant for the Professional Rodeo Cowboys Association.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More