Abstract. Forty nine quarters from 24 lactating cows with chronic mastitis were selected and assigned to experimental groups, according to the number of the somatic cells in their milk:
- 10 quarters, somatic cell count: 50-100×104/ml
- 14 quarters, somatic cells count: 100-300×104/ml
- 18 quarters, somatic cells count: >300×104/ml
- Control group, treated with norfloxacin ointment
After treatment, the milk of the control group contained insignificantly lower numbers of somatic cells and bacteria on day 7 compared to pretreatment levels. Experimental groups A, B and C had lower somatic and bacterial cells in their milk on day 7 compared to pretreatment levels. Experimental groups B and C had significantly lower numbers of somatic cells in their milk on day 7 than before treatment (p<0.01). However, an insignificant difference in somatic cell numbers was detected between the control and experimental groups. It was concluded that ozone therapy with ozonated oil applied on bovine mastitis might be effective.