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studies have assessed the biochemical or haematological characteristics of donkey blood using study animals from distinct populations from around the world. A previous study by French and Patrick (1995) established reference intervals using a similar UK donkey population to the current one and these reference values have been used by The Donkey Sanctuary for clinical assessment of resident and nonresident animals for nearly 20 years. It is timely to review those previously published reference intervals in view of changes in methods and technologies at the diagnostic laboratory of the Donkey Sanctuary. In addition, nutritional and other management practices have evolved with the increase in understanding of the unique requirements of donkey, and these developments could affect physiological parameters. It was not possible to directly compare these new RIs with


those of the study by French and Patrick (1995) as the raw data for the former was not available. In any case analytical equipment used was not the same in each study and 3 parameters (PLTs, RDW% and bile acids) had not been previously established. To assess the transferability of these new RIs with those developed for other populations reference interval transference validation was undertaken. When RI transference validation was undertaken, 15/18 haematological and 14/19 biochemical RIs were transferrable between previous donkey RIs and these RIs. However, on closer inspection, it is likely that many of the RIs established by Patrick and French are inappropriately wide for this population and should not be viewed as transferrable. On inspection of the RI transference data it can be seen that 12 of 19 biochemical RIs showed 100% transference and 9 of 16 haematological RIs showed 100% transference. Such high levels of agreement are likely due to inappropriately wide RIs and according to ASCVP guidelines should be viewed with caution (Anonymous 2011b). It is noted that the RIs reported for many analytes demonstrated significant ‘narrowing’ of the RIs in this study when compared with the study by French and Patrick (1995). Of particular clinical note when comparing the new


donkey RI with that reported previously is a narrowing of the reference intervals for triglycerides with the upper limit of the range being 2.8 mmol/l as compared with the previous 4.3 mmol/l. It is very important that veterinarians note this difference as this upper limit of triglycerides is commonly used to determine the risk of a donkey becoming hyperlipaemic; donkeys with plasma triglyceride concentration above this limit would normally begin treatment to correct an ensuing negative energy balance. Clinicians should be alert to the fact that, depending on signalment and laboratory methods used, use of an upper reference limit of 4.3 mmol/l for triglycerides may not be appropriate and indeed could be risky for the donkey in their care. Notwithstanding effects due to changes in methods and technology between these UK studies, it is also likely that there are physiological reasons for the differences noted. The study by French and Patrick (1995) was based on an admirably large cohort (n = 4238); however, both clinically normal and diseased donkeys were included in the study thus greater divergence of the upper and lower limits of the reference intervals could be expected due to the variable effects of disease processes on various parameters. The current study sought to establish appropriate reference values only for clinically healthy donkeys thus individuals were subjected to stringent clinical checks before inclusion in the study.


It is not possible to directly compare the RIs developed in


this study with those reported in other studies. Reference intervals generated by different instruments and using variable techniques are not comparable and the differences between the populations studied by others and this cohort are also limiting. Limited comparisons can be made by RI transference validation. This validation was carried out to compare these donkey RIs with those produced for donkeys resident in Mexico (de Aluja et al. 2006) and Ethiopia (Lemma and Moges 2009). Results showed limited transferability between the RIs reported for this population and those reported for working donkeys in Mexico. In particular, many of the RIs reported by de Aluja et al. (2006) were significantly narrower than those reported in this study. This is perhaps unsurprising as the population studied was smaller (n = 48), had previously been working animals and were kept under different conditions to the cohort used for this study. Determination of transference with haematological RIs


established for working donkeys in Ethiopia was limited to a smaller number of analytes reported by the study of Lemma and Moges (2009). Reference intervals transference was possible in 5 out of 6 analytes assessed suggesting that RI transferability was high for these analytes between the 2 RIs. Further work would be useful to determine if transferability is also possible for a wider range of haematological analytes and biochemical analytes. With such a globally ubiquitous species the aspect of


relevance of published reference intervals to local populations is important. The differences between studies may be due to differing diagnostic or storage techniques or may reflect differences in management and use of the donkeys studied. Best practice dictates that RIs should be established for each population encountered by a laboratory and that transference of RIs between laboratories and contexts should be undertaken with great caution. Where establishment of specific RIs for donkeys is not possible within a given context, reasons for disparity between ‘local’ results and RIs such as those reported here must be borne in mind. For example, in contexts where donkeys are working (Lemma and Moges 2009; Etana et al. 2011; Girardi et al. 2013), it may be expected that haematological RIs such as haematocrit (calculated PCV) and biochemical parameters such as CPK are effected by work undertaken. Parasitism also likely represents an additional variable in some populations, for example, liver fluke (Fasciola spp.) is known to be endemic in donkeys in many parts of Ethiopia (Getachew et al. 2010) and may be expected to contribute to the significantly higher liver enzymes as reported in other studies (Lemma and Moges 2009; Etana et al. 2011). Gut endoparasite burdens may be responsible for significant differences in parameters such as RBC, TP and Eos due to intestinal damage and inflammatory responses and will make transference of RIs challenging in populations with very different parasite challenges. Differences in feeding practices may impact significantly, but variably, on RIs and their transference between contexts. For example, markedly high triglyceride levels are reported by Al-Busadah and Homeida (2005) in donkeys fed on a sugar- and fat-rich diet comprising mainly dates, whilst serum creatinine levels could vary with diets rich in protein or in donkeys with more developed muscle mass. Many previously published studies on donkeys have


focused on specific breeds (Folch et al. 1997; Jordana et al. 1998; Al-Busadah and Homeida 2005; Caldin et al. 2005;


© 2015 The Donkey Sanctuary. Equine Veterinary Education published by John Wiley & Sons Ltd. on behalf of EVJ Ltd.


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