OBJECTIVE To identify clinical or clinicopathologic variables that can be used to predict a positive PCR assay result for Anaplasma phagocytophilum infection in equids. ANIMALS 162 equids. PROCEDURES Medical records were reviewed to identify equids that underwent testing for evidence of A phagocytophilum infection by PCR assay between June 1, 2007, and December 31, 2015. For each equid that tested positive (case equid), 2 time-matched equids that tested negative for the organism (control equids) were identified. Data collected included age, sex, breed, geographic location (residence at the time of testing), physical examination findings, and CBC and plasma biochemical analysis results. Potential predictor variables were analyzed by stepwise logistic regression followed by classification and regression tree analysis. Generalized additive models were used to evaluate identified predictors of a positive test result for A phagocytophilum. RESULTS Total lymphocyte count, plasma total bilirubin concentration, plasma sodium concentration, and geographic latitude were linear predictors of a positive PCR assay result for A phagocytophilum. Plasma creatine kinase activity was a nonlinear predictor of a positive result. CONCLUSIONS AND CLINICAL RELEVANCE Assessment of predictors identified in this study may help veterinarians identify equids that could benefit from early treatment for anaplasmosis while definitive test results are pending. This information may also help to prevent unnecessary administration of oxytetracycline to equids that are unlikely to test positive for the disease.

OBJECTIVE To determine the influence of various neck positions on cervical vertebral radiographic measurements in horses. ANIMALS 18 client-owned horses examined for lameness but free of cervical disease. PROCEDURES Laterolateral radiographs of the cervical vertebrae from C1 through T1 were acquired for each horse in 3 neck positions (low, neutral, and high). Minimum sagittal diameter, intravertebral sagittal diameter (intra-VSD) ratio, inter-VSD ratio, length of the articular processes joint ratio, vertebral alignment angle, and vertebral fossa angle were measured at each segment in each neck position. Values for the high and low positions were compared with those for the neutral position. RESULTS No significant differences from neutral position values were identified for minimum sagittal diameter, intra-VSD ratio, and vertebral fossa angle as measured in low and high neck positions. Compared with results in the neutral position, the high position resulted in a greater vertebral alignment angle at C3–4 and inter-VSD ratio at C4–5 and a lower length of the articular processes joint ratio at C2–3, C3–4, and C4–5; the low position resulted in a lower vertebral alignment angle at C4–5. However, all observed differences were small. CONCLUSIONS AND CLINICAL RELEVANCE Neck position influenced some radiographic measurements of the cervical vertebrae in horses free of cervical disease. However, because several of these measurements were not or were only minimally affected by neck position, some latitude in neck position may be possible without concern about substantially affecting radiographic measurements in this region.