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Microcytosis is observed in healthy Japanese breed dogs. The aim of the study was to evaluate the frequency and intensity of asymptomatic anisocytosis using a three-grade scale in Japanese dog breeds with special emphasis on the following indices: mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration, and red blood cell distribution width. The retrospective study included analyses of blood morphology and blood smear for clinically healthy Japanese dog breeds Shiba, Akita, and Hokkaido aged from 6 months to 14 years, performed as a part of preventative care. A total of 74 dogs of both sexes were qualified for the study. The group included both neutered and non-neutered animals (Akita – 17 females, 12 males, Shiba – 24 females, 18 males, Hokkaido – 2 females, 1 male). The blood smear revealed significant anisocytosis in 60.8% and mild anisocytosis in 28.4% of the tested dogs – 89.2% in total. Microcytosis was reported for 25.7% of the tested Japanese breed dogs. Reduced mean cell haemoglobin and mean cell haemoglobin concentration were diagnosed in 75.7% and 40.5% of dogs, respectively. Red blood cell distribution width as an anisocytosis indicator exceeded the norm in 12% of the tested dogs. Compared to mixed breed dogs, the Japanese breeds had a reduced mean cell volume, mean cell haemoglobin concentration and significant anisocytosis in the blood smear as well as a higher red blood cell distribution width indicator. Veterinarians should consider these differences when interpreting the results of morphological blood tests. MCH, MCHC, red blood cell distribution width Red cell distribution width (RDW) as an anisocytosis indicator is a quantitative measure of the range of variation of the circulating red blood cells (Neiger et al. 2002; Hodges and Christopher 2011; Montagnana et al. 2012; Mazzotta et al. 2016). It is a routinely measured indicator by haematology analysers (Lippi and Plebani 2014). This indicator is usually elevated when insufficient total red blood cell count (RBC) production is observed as a result of e.g. vitamin B12 or iron deficiency, exacerbated red cell destruction, haemolysis, after a blood transfusion or in severe inflammatory states. Changes in this indicator are observed in the course of numerous systemic conditions such as renal diseases or nutrition shortages (Hellhammer et al. 2016). Increased RDW is also observed in cases of RBC deformability (Patel et al. 2013). It is also treated as an indicator for evaluation of red blood cell functionality (Patel et al. 2013; Lippi et al. 2014). Red cell distribution width is a valuable prognostic lethality marker for humans in the course of heart diseases (Campora et al. 1987; Felker et al. 2007; Aung et al. 2013). Changes in the haematology for different dog breeds have been documented. Separate referential values were established for Greyhounds, which have higher haematocrit (HCT), mean cell volume (MCV) and haemoglobin (HGB) concentration and a lower total platelet count (PLT) and total white blood cell (WBC) count compared to other breeds (Porter and Canaday 1971; Sullivan et al. 1994; Guyton and Hall 2006; Campora et al. 2011; Zaldivar-Lopez et al. 2011). Physiological macrocytosis was diagnosed in miniature breeds and standard ACTA VET. BRNO 2017, 86: 385–391; https://doi.org/10.2754/avb201786040385 Address for correspondence: Olga Aniołek St. Nowoursynowska 100 02-797 Warsaw, Poland Phone +48 (22) 593 60 92 E-mail: [email protected] http://actavet.vfu.cz/ poodles (Schalm 1976). Compared to mixed breed dogs, Dachshunds have a higher mean platelet volume (MCV), HCT, RBC and a higher HGB concentration (Torres et al. 2014). Idiopathic thrombocytopaenia connected to beta-tubulin mutation in Cavalier King Charles Spaniels (Singh and Lamb 2005; Davis et al. 2008) or microcytosis in Asian dog breeds reported in literature (Tanabe 2006; Battison 2007) can serve as another example. Increased popularity of breeds such as Shiba or Akita has been recently observed in Poland, sparking the need to analyse asymptomatic microcytosis in more detail. The aim of the study was to evaluate the frequency and intensity of asymptomatic anisocytosis using a three-grade scale in Japanese dog breeds with special emphasis on the indices of MCV, mean cell haemoglobin (MCH), mean cell haemoglobin concentration (MCHC), and RDW. Materials and Methods