The Horse

SEP 2017

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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32 TheHorse.com THE HORSE September 2017 medicine clinician from the Department of Medicine and Epidemiology at the University of California, Davis, School of Veterinary Medicine, determined that SAA helps differentiate between these conditions. In their study, published in 2016 in the Journal of Equine Veterinary Science, he and colleagues measured SAA levels in 207 horses. Those horses were diagnosed with one of the following—influenza (42), equine herpesvirus-4 (43), IAD (38), S. equi ss equi (44)—or served as healthy controls (40). Key findings were: ■ Most healthy horses had undetectable SAA levels (0-2 mg of SAA/L of serum); ■ Only six horses with IAD had detect- able SAA values, with a maximum of 586 mg/L; ■ Horses confirmed to have influenza had SAA values ranging from 0 to >3,000 mg/L and a median value of 731 mg/L; ■ Horses diagnosed with EHV-4 had similar ranges of SAA (from 0 to >3,000 mg/L) but a median value of 1,173 mg/L; and ■ Infection with S. equi ss equi resulted in SAA levels from 0 to >3,000 mg/L with a median value of 1,953 mg/L. "All three groups of horses diagnosed with a respiratory condition had SAA lev- els significantly higher than the healthy control horses, including the IAD group," says Pusterla. "The IAD group had signifi- cantly lower SAA values than each of the three groups with infectious respiratory disease. Horses diagnosed with bacterial respiratory infection, in this case S. equi ss equi, had significantly higher SAA lev- els than horses with the viral respiratory tract infections." Pusterla did point out, however, that despite the significant difference in SAA values between horses with bacterial and viral infectious respiratory diseases, there is a lot of overlap in SAA values between these two groups. "The findings of this study do not suggest that SAA levels alone be used to distinguish between bacterial and viral respiratory diseases," he says. "Other tests must be conducted, such as culturing nasal secretions or polymerase chain reaction. "This test can also be used in appar- ently healthy horses prior to transport, competition, or even surgery to ensure the health of their respiratory tracts for maximal health and performance," Pusterla adds. Specifically, measuring SAA levels in horses to ensure they're normal prior to transport could be useful because horses commonly develop respiratory disease during and following long-distance trailering. Transport can also exacerbate an underlying respiratory tract infection, making it important to identify horses with latent respiratory issues. "Underlying infections caused by respiratory viruses could potentially be identified via SAA measurements, and horses with elevated SAA levels prior to transport likely should not undergo transport until those SAA values return to normal levels, meaning almost undetect- able," says Pusterla. Castro concurs, adding that veterinar- ians use SAA routinely not only in race- horse but also show horse populations. "They do a lot of traveling, and measuring pre- and post-transport levels of SAA con- tinues to increase in popularity," he says. Musculoskeletal Conditions There is a long history of researchers studying SAA in conjunction with various musculoskeletal issues. In general, SAA levels remain negligible in the face of in- flammation (e.g., training-related strains to tendons or ligaments, fractures, etc.); infections cause much more profound SAA increases. Take, for example, a condylar fracture: If there is inflammation but no infection, SAA levels should be normal. Monitoring that same horse after surgical repair of the fracture could reveal infection (e.g., from the implants used or surgical site contamination). "SAA should not rise following surgery to repair a condylar fracture if there is no infection," Castro says. He gives another example: cellulitis, which is usually apparent as a severely swollen limb. "A simple cellulitis, al- though remarkable to look at in a horse, will not necessarily increase SAA levels unless there is an infectious component." Where SAA does come in handy is for detecting conditions such as joint infec- tions (septic arthritis) following adminis- tration of intra-articular medications or puncture of a synovial structure. The marker can also help veterinar- ians detect infection in horses that aren't performing up to snuff. "Precompetitive testing of SAA to determine if a horse has a subclinical Stallside SAA test kits now allow veterinarians to get accurate readings in real time. COURTESY STABLELAB Getting a Read on INFECTION Horses diagnosed with bacterial respira- tory infection … had significantly higher SAA levels than horses with the viral respiratory tract infections." DR. NICOLA PUSTERLA

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