Texas Equine Veterinary Association

www.texasequineva.com • 14 an acute phase biomarker, used to detect equine infections, monitor treatments and screen for at risk patients Serum Amyloid A Serum Amyloid A (SAA) is a major acute phase protein the liver produces in the face of inflammation caused by an infection that is changing the way equine veterinarians practice medicine. Within hours of the body being exposed to an infectious agent, the liver produces high enough levels of SAA that can be measured in the general circulation. Circulating SAA levels rise rapidly and dramatically into the hundreds to thousands during infection. The obvious advantage of this biomarker is that veterinarians can rapidly diagnose a patient with an infectious condition often prior to visible or outward clinical signs such as fever, nasal discharge, diarrhea, etc. As quickly and dramatically as SAA elevates, its levels also decrease quickly, approximately 50% every 24 hours, once the infection is resolved, enabling serial monitoring of SAA to monitor the horse's response to treatment over time. (1, 2) Monitoring response to treatment by measuring SAA daily to every other day is one of the most common ways equine practitioners use SAA. Repeat testing is extremely important to identify and track where the typical response curve the horse is in addition to identifying what side of the peak response the horse may be (Figure 1). An example of this would be keeping the horse on antibiotics until the SAA drops down to close to normal range, you would then know that the horse is on the right track and it's own immune system will continue to manage the infection. Conversely, if the incorrect antimicrobial is being used SAA levels will continue to rise in the face of treatment, you could surmise that a change in antibiotics is indicated. Likewise, if a "wait and see" approach is utilized and the SAA levels continue to rise, you should consider starting that horse on antibiotics sooner before the problem gets out of hand. This article will go over how to use SAA to help identify common equine disorders of the respiratory, musculoskeletal, and abdominal tract. It also outline the benefits of testing SAA levels in healthy horses, including foals. RESPIRATORY TRACT CONDITIONS Differentiate between infectious versus non-infectious respiratory disease. (4) Veterinarians are commonly called out to diagnose and treat horses with poor performance, exercise intolerance, coughing, and nasal discharge. The list of potential causes for these complaints can be quite long, including equine influenza (flu), equine herpes virus (EHV 1 or 4), infection with the bacterium Streptococcus, equi subspecies equi, and even noninfectious inflammatory airway disease (IAD), otherwise known as equine asthma, recurrent airway obstruction or chronic obstructive pulmonary disease. In a recently published study, by Dr. Molly Viner (4) and colleagues Figure 1: Typical SAA Response Curve vs. Typical Fibrinogen Curve By Amy Poulin Braim, VMD, DACVS- LA, a Senior Equine Technical Services Veterinarian with Zoetis. and Bobby Cowles, DVM, MS, MBA, a Managing Equine Technical Services Veterinarian with Zoetis.

• Cover