Vetnews | Mei 2025 24 « BACK TO CONTENTS Article 4. Discussion One goal of this study was to establish reference intervals for hematologic and biochemistry values in healthy adult donkeys at the AHDC, as a means of bolstering submitting veterinarians’ ability to make accurate diagnoses in this unique equid species. To best represent the donkey population that is typically tested at the AHDC, the reference population was assembled from a wide geographic range throughout the U.S. and included mostly standard-sized donkeys, followed next by miniature donkeys and a single mammoth donkey. Intact male donkeys did make up a large proportion of the CBC (49%) and biochemistry panels (46%) performed for this study because these samples were convenience samples obtained just prior to a scheduled mass castration event at the facility where the animals were housed. Wild donkeys roam freely across much of the Western U.S. The Bureau of Land Management (BLM) estimates there are currently over 14,000 free-roaming donkeys in herd management areas in Arizona (AZ), California (CA), Nevada (NV), Oregon (OR), and Utah (UT) as of 1 March 2024 [19]. One of the approaches that the BLM utilizes for population control is the periodic removal and capture of wild donkeys from these lands, with subsequent adoption into private care. To account for this in our reference population, approximately 20% of the CBC and chemistry data were obtained from free-roaming donkeys upon capture in Butte Valley, an area within Death Valley National Park, CA. An additional goal of this study was to analyze at least 120 samples to establish robust reference intervals and utilize nonparametric statistical methods, a process that minimizes the effect of outliers and is recommended to best characterize a population [18]. Animal availability, submitter compliance, and sporadic sample issues, however, reduced the number of acceptable samples slightly below the intended threshold, and statistical methods were adjusted to best characterize the data for each analyte. Most outliers removed were repetitive findings deemed to be the result of common pre-analytical artefacts (e.g., uneven WBC distribution on blood smears, platelet clumping causing false thrombocytopenia, delayed serum separation from cells causing false hypoglycemia, capture and handling causing increased CK). Other outliers removed were generally a single analyte from a single specimen and had a minimal impact on the reference interval calculation. Two exceptions were GGT and lipid values. Initial GGT analysis revealed several high suspect and outlier data points, creating a wide reference interval with a right-tail skew (Figure 1). Analysis of the results revealed that 6/10 of the highest values came from a single herd whose samples were submitted as whole clotted blood samples. Previous and subsequent biochemistry bloodwork from those donkeys, sent to a different laboratory, all had significantly lower GGT levels, so an unknown artefact is presumed to have occurred in this case. Further, 3/10 of the remaining highest GGT values were then discovered to have come from a separate single herd source, and that herd was reported to have a history of liver flukes. Removal of these GGT outliers produced a data spread and reference interval more typical of the expected variation (Figure 2). A few cholesterol and triglyceride outliers were also removed from the analysis. These results came from various ages and premises, but their pattern of results suggested subclinical hyperlipidemia was likely present in these individual animals. Removal of these GGT and lipid outliers was a subjective decision, as definitive disease or error could not be determined. However, the authors felt that their removal was the most appropriate decision based on their combined clinical and laboratory experiences. Reference intervals generated by this study are similar to a 2016 study by Burden and colleagues, representing 138 donkeys in the United Kingdom [13]. Of particular note is that the TG RI (0.3–2.2 mmol/L) corresponds closely to their TG RI of 0.6–2.8 mmol/L, a significant difference from an earlier large UK study [20]. Metabolic disorders in donkeys are a common problem and are associated with a high morbidity and mortality rate. Hyperlipemia was previously defined as the fatty infiltration of organs with a serum TG concentration >4.4 mmol/L [21], but this study supports the theory that a lower cutoff would be more appropriate to recognize donkeys at risk for developing hyperlipemia. This study also supports the concept that species-specific reference intervals are critical to evaluate patients, as important differences were noted between the AHDC’s previously established equine (horse) RIs, previously established donkey RIs from other studies, and these newly derived donkey RIs, especially in key analytes like TGs and GGT, as shown in Table 5. Complete Blood Count and Biochemistry Reference Intervals for Healthy Adult Donkeys in the United States <<<23 Dir Bilirubin umol/L 117 0 0.3 0 0 1.7 <0.001 NG NP 0 1.7 0–0 0–1.7 Indir Bilirubin umol/L 117 1.7 0.9 1.7 0 1.7 <0.001 NG NP 0 1.7 0–0 1.7–1.7 CK U/L 112 231 105 210 47 725 0.055 G P 95 500 86–105 446–569 Cholesterol mmol/L 114 2.0 0.4 2.0 1.3 3.2 0.281 G P 1.4 2.4 1.3–1.5 2.8–3.1 Triglycerides mmol/L 113 1.2 0.5 1.2 0.1 2.4 0.273 G NP 0.3 2.2 0.2–0.4 2.0–2.3 Figure 1: Initial GGT analysis prior to outlier removal, shows several high suspect (orange X) and outlier (red *) data points, creating a wide reference interval with a right-tail skew. Figure 2: GGT analysis after outlier removal, showing a data spread and reference interval more typical of expected variation. A single outlier (red *) remains from an apparently healthy donkey.
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