The smears were stained using May–Gru¨nwald and Giemsa stains (Lucas and Jamroz, 1961), approximately 2–4 h after preparation with methyl alcohol fixation. One hundred leukocytes, including granular (heterophils, eosinophils, and
basophils) and non-granular (lymphocytes and monocytes), were counted on one slide of
each bird, and the heterophil to lymphocyte ratio was calculated.