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.

Surgery confirmed the diagnosis in half the cases and provided access to remove the abscess. Arnold reported finding a gastrointestinal foreign body in 15 horses--wire was the predominant material, which the horses likely consumed when eating wire-baled hay. Three-quarters of the 61 horses were euthanized because of poor prognosis related to peritonitis (abdominal infection), adhesions, or an owner's financial constraints. Of the 18 horses that continued treatment, veterinarians administered antimicrobials, with length of treatment dependent on infection severity and number of bacteria isolated from abscesses. A variety of pathogens were cultured from three-quarters of these horses under treatment. Fifteen of the 18 horses survived and were discharged from the hospital.

Arnold concluded that helpful diagnostic information in abdominal abscess cases can be obtained through ultrasound and rectal exam, cytology of abdominal fluid, and abdominal exploratory surgery.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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