The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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34 TheHorse.com THE HORSE September 2017 disease despite having no cough or fever with a history of poor performance can be extremely helpful," Castro says. "In some cases we find walled off abscesses in lungs that can't easily be detected by other methods." Gastrointestinal Tract Disease For decades veterinary researchers have tried to find a test that can clearly determine whether a colicky horse needs surgery. Can SAA fit the bill? Castro says the answer is no. "Do not rely on SAA to determine if a colic is surgical or not," he says. "Use the standard techniques, such as response to analgesics (pain-relievers). Monitoring horses that underwent surgery, however, is another case. SAA can indicate whether a horse is fighting an infection postop- eratively. Infections can easily occur in horses that had a section of their gastro- intestinal tract removed." Veterinarians can, however, use SAA readings to help differentiate between infectious causes of colic, such as perito- nitis and colitis, and noninfectious forms, says Pusterla. Assessing Foal Health Breeders often use an immunoglobulin G (IgG) kit to measure foals' blood anti- body levels to confirm passive transfer of immunity from the mare's colostrum (first milk). While ingesting a sufficient amount of good-quality colostrum puts them on the path to thrive, these new- borns still are delicate creatures that can easily contract life-threatening infections. Respiratory and gastrointestinal issues are not uncommon. "Because the immune system in young foals is not mature, we often see SAA lev- els increase in sick foals a lot higher and a lot quicker than in more mature horses," says Castro. "Anything greater than 200 is concerning." He adds, "SAA might also be used as a screening tool for Rhodococcus equi, which causes abscesses in the lungs. Right now, ultrasound is widely used to screen foals for lung abscesses … . Instead, SAA can first be measured. If the value is 0, there is no need to ultrasound." How to Test SAA Like any blood test, there are several ways veterinarians can measure SAA. Some send a blood sample to a laboratory for analysis; however, SAA can degrade in the sample during transport, making the values 5-10% lower than the actual SAA levels. Also, test results won't be available for a few days. Because one of SAA's features is its "real-time" measure of inflammation, manufacturers have developed several stallside test kits that provide practitioners with accurate and immediate results. Regardless of which process your veter- inarian employs, it's important to be sure the test's units are consistent and match the reference ranges he or she is referring to. For example, the University of Miami Miller School of Medicine measures equine SAA in mg of SAA/L of serum, while Cornell University's Animal Health Diagnostic Center measures micrograms (μg)/mL of serum. Conveniently, in this case mg/L is the same as μg/mL; however, other laboratories report SAA values in mg/dL (deciliter), which is not the same. Online calculators can help with SAA value conversions for comparing different lab values and horse test results. Regard- less, the SAA value should come with various reference ranges for intrepreta- tion (e.g., normal, mildly elevated, etc.). Take-Home Message Equine veterinarians are finding serum amyloid A values useful in a variety of cases, but it's important to remember they are only one piece of a puzzle. "Every infection has inflammation, but not all inflammation has infection," says Castro. "Horses with pure inflammatory conditions, such as tying-up or laminitis, that do not have an underlying infectious component will not have increased SAA levels. In these cases, other diagnostic tests are needed to help diagnose disease and monitor response to treatment." Nonetheless, this test can help prac- titioners detect infectious conditions quickly and guide treatment strategies for optimal outcomes and return to function. "The faster an infectious condition is di- agnosed, the quicker the veterinarian and barn staff can work together, instituting appropriate biosecurity protocols to mini- mize disease spread," Pusterla says. h SAA's Beginnings Historically, veterinarians detected and monitored inflammation and infection based on the horse's history and clinical presentation (being dull, lacking energy, not interested in eat- ing). One of the first true measures of "illness" simply involved tracking body temperature via rectal thermometer. Next came analysis of white blood cell counts (a complete blood cell count), then various acute phase proteins such as fibrinogen, haptoglobin, 1-acid glycoprotein, and C-reactive protein. Years of research (beginning in the 1980s) subsequently identified serum amyloid A as an improved method of detecting inflammation/ infection.—Stacey Oke, DVM, MSc Getting a Read on INFECTION SAA measurements might be particularly useful in sick foals, whose levels increase much higher and faster than mature horses'. THE HORSE STAFF