Haematological findings in 158 dairy cows with toxic mastitis with a focus on the leukogram

Abstract Background: Acute toxic mastitis is characterised by typical clinical findings and changes in the leukogram. The goal of our study was to compare the leukogram of 158 cows with toxic mastitis and 168 clinically healthy cows. The cows were examined clinically and underwent haematological and biochemical examination of blood and bacteriological culture of milk samples. Results: All cows with toxic mastitis were ill and had a poor appetite or anorexia, and 34 cows (21.5%) were recumbent. A single quarter was affected in 119 cows (75.3%), two quarters in 37 cows (23.4%) and three quarters in two cows (1.3%). Bacteriological culture showed gram-negative pathogens in 100 cows (63.3%), gram-positive in 15 (9.5%) and yeast in 4 (2.5%). The median total leukocyte count of ill cows was 4,300 cells/µl, which was significantly lower than 8,000 cells/µl in controls. With the exception of band neutrophils and metamyelocytes, the counts of all components of the leukogram were lower in ill cows compared with controls. Significantly more cows with toxic mastitis had leukopenia (60.1 vs. 4.1%) or leukocytosis (10.1 vs. 3.0%) than controls. Ill cows had significantly lower segmented neutrophil counts than controls (860 vs. 2,598 cells/µl), and 69.5 and 17.3%, respectively, had counts below the reference interval. Ill cows had increased band (77.3%) and metamyelocyte (25.0%) counts compared with control cows (0.6 and 0%, respectively). In ill cows, eosinopenia occurred in 66.4% (controls, 1.8%), monocytopenia in 40.6% (controls, 4.2%) and lymphopenia in 60.2% (controls, 1.8%). Twenty-one ill cows (16.4%) had a regenerative and 57 (44.5%) had a degenerative left shift. The median neutrophil-to-lymphocyte ratio was 0.97 in ill cows and 0.63 in controls. Toxic changes in neutrophils including cytoplasmic basophilia and vacuolisation were seen in 101 (91.8%) of 110 blood smears of ill cows.Conclusions: Acute toxic mastitis results in severe changes in the leukogram particularly leukopenia, lymphopenia and degenerative left shift. The leukogram has significant diagnostic value and may aid in the modification of treatment when needed.