A variety of equine conditions can present with clinical signs that include colic pain, fever, decreased appetite, and weight loss. Similar signs occur with abdominal abscesses, making them challenging to diagnose. At the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md., Carolyn Arnold, DVM, Dipl. ACVS, clinical assistant professor of veterinary medicine at Texas A&M University, discussed data from a retrospective study of 61 cases of abdominal abscesses in adult horses.

Arnold defined an abdominal abscess as an encapsulated structure within the abdominal cavity that contains an exudate (pus). Veterinarians diagnosed the abscesses on ultrasound, during surgery, or at necropsy. Horses in the study ranged from 1-23 years old, and there was roughly equal distribution between male and female. The predominant clinical signs detected in association with these abdominal abscesses were abdominal pain (67%), depression (57%), lack of appetite (51%), fever (46%), rapid heart rate (46%), and weight loss (30%).

Precipitating events in these cases included recent castration, a penetrating wound, previous abdominal surgery, or exposure to Streptococcus equi bacteria. One affected mare had suffered a vaginal laceration subsequent to foaling. Twenty-five percent presented with acute clinical signs, such as colic, whereas 75% displayed chronic clinical signs despite ongoing treatment by referring veterinarians.

Veterinarians identified a mass on rectal exam in a quarter of the affected horses. Ultrasound via rectal scan or external scan along the abdomen identified an abscess in 56% or an abnormal amount of abdominal fluid (ascites) in 45%. Most horses (47) had a single abscess; the rest had two or more abscesses present