EXPERIMENTAL SUBCLINICAL MASTITIS IN HOLSTEIN COWS BY INTRAMAMMARY INOCULATION OF Staphylococcus aureus (STRAIN ATCC 25923).

Abstract

Staphylococcus aureus is the major bacteria involved in cow intramammary infections and it represents an important concern to public health and to the milk production over the world. S. aureus is the most prevalent organism isolated in milk samples from infected mammary glands, in Brazil. The goal of this study was to verify the viability of the experimental model of bovine subclinical mastitis induced by S. aureus inoculation and to evaluate the clinical and laboratory results related to the infection. It were examinated 40 mammary quarters from 12 health Holstein cows, submitted to two procedures: Group 1: ten not inoculated mammary quarters; and Group 2: thirty mammary quarters inoculated with 500 CFU of S. aureus (strain ATCC 25923). This method induced subclinical mastitis in 63.3% of the inoculated mammary quarters. Total cell count was significantly higher in milk samples from group 2 obtained 72 hours after bacteria inoculation (2,432.20 x 103 cells/mL), showing tissue inflammatory response, in comparison with not inoculated quarters. Milk total protein concentrations were not influenced by inflammatory response induced by S. aureus and the values ranging from 4.26±0.61 to 4.38±0.40 g/dL, in group 1, and from 4.28±0.43 to 4.47±1.00 g/dL, in group 2. KEY-WORDS: Subclinical mastitis. Cows. Staphylococcus aureus. Experimental infection.