Speciation of actinomycetes is not a routine diagnostic procedure and 16S rRNA gene sequencing to identify A. denticolens as a cause of soft-tissue abscessation in horses in Australia has not been previously described. Practitioners should include this bacterial species in their differential diagnosis, particularly if abscesses do not respond to drainage and lavage alone.

A 10-week-old Thoroughbred filly was referred for anaemia of 4 weeks' duration. Haematology revealed severe anaemia and panleucopenia. Cytological examination of bone marrow smears revealed a myeloid to erythroid ratio <0.02:1 (reference range 0.5-2.4:1.0) and an abundance of erythroid precursor cells. The erythroid cell population included rubriblasts, prorubricytes and rubricytes, with only scant numbers of metarubricytes present. There were numerous mitotic erythroid cells, some of which were atypical and megaloblastic. These cytomorphological changes are consistent with pure acute erythroid leukaemia. No treatment was instituted and the filly died three days after presentation. This case illustrates the need to consider both haematology and bone marrow findings to establish a diagnosis of pure erythroid leukaemia. To our knowledge, there is no documented case of acute myeloproliferative disease in horses involving cells of erythroid lineage, but this condition should be considered a differential diagnosis for horses presenting with anaemia.