Q: I have an 11-year-old maiden mare—a Thoroughbred/Holsteiner cross—who has had two swollen areas just in front of her udder for months. Otherwise she is healthy, has a great appetite, interacts with her herdmates and, according to the veterinarian, has a perfect body condition score. 

            She is extremely sensitive when I try to touch her udder, but she doesn’t mind when I clean it with a hose that has a pretty strong pressure. At her last semiannual exam, the veterinarian said the swelling may be due to her swishing her tail under her belly to swat
flies and gnats. But even when the weather is cold and there are no insects to annoy her, the swelling remains. What could this be? I am concerned it might be some type of infection or even cancer.
Lillian Lampros; Sylva, North Carolina

A: I would need answers to several questions before I could make a fully informed guess at your mare’s condition, but first I will suggest what seems to me the most likely cause.

The area just in front of the udder is a popular target for insects, and bites there can cause acute swelling, itching and crusting. Since there is often some loose tissue there, any swelling can be prominent. If this swelling recurs over a few years, some thickening scar tissue will build up from repeated insults, so the enlargement can remain after insect season.

Regarding her sensitivity to touch, I would ask: Has she always been sensitive, or has this developed recently? If she has always reacted negatively to contact there, her response may be behavioral rather than physical. Many mares guard this personal space and will resist being touched. Try to desensitize the area with advance/retreat and reward procedures. Her response to that training will let you know whether her reactions stem from pain or simply from being behaviorally sensitive to your “invasion” of that area.

To better assess your mare from a medical standpoint, I would ask several questions:

  1. Is the skin in the swollen area normal, crusty, moist or thickened?
  2. Has it ever drained any fluid or pus?
  3. Is it larger, smaller or the same size as it was a few weeks or months ago?
  4. Are the swollen areas symmetrical on either side of the midline?
  5. How large are they?
  6. Are they soft or firm?

I think it is unlikely that the swellings result from infection or cancer if the size has been essentially constant and the overlying skin is normal. But I would suggest that you make a list of your answers to these questions and have another discussion with your veterinarian. Should any doubts remain, an ultrasound examination of the swellings, and perhaps biopsy, would provide definitive answers.

Jim Latham, DVM 

Patty Latham, DVM
Mill Creek Veterinary Service
Pagosa Springs, Colorado