Intra mammary challenge of dairy goats with a low dose of Staphylococcus aureus

Abstract

The aim of this pilot study was to induce a subclinical mastitis in dairy goats with a bovine Staphylococcus aureus (S. aureus) strain and to investigate the post infection (p.i.) response during the first 48 hours of this infection. The right udder halves of 2 goats were inoculated with approximately 58 Colony Forming Units (CFU) of S. aureus in 1 ml phosphate buffered saline (PBS) 45 days after parturition, The other 2 goats served as negative controls. General health examinations and milk samples were collected from all animals just prior to inoculation and 6, 12, 24 and 48 hours after inoculation. Blood samples were taken just before inoculation and 24 hours and 7 days after inoculation. The infected animals were treated with antibiotics 48 hours after inoculation. Bacteriological analysis were performed in the milk samples within two hours after collection. The total white blood cell count and a differentiation of these cells were obtained from the blood samples. According to the results of the bacterial counts the inoculation of the two goats lead to an infection of inoculated udder halves. One goat showed S. aureus in her milk at 6, 12 , 24 and 48 hours after inoculation while S. aureus was isolated from the milk of the other inoculated goat only at 24 and 48 hours after inoculation. The uninoculated animals did not show an intra mammary infection. Furthermore none of the animals (inoculated or not inoculated) showed any clinical signs nor significant differences in blood values during the trial. Based on these results can be concluded that the dose used in this pilot study has successfully induced a subclinical mastitis. Conclusion: this experiment shows that a subclinical mastitis can be induced in dairy goats with this low dose of S. aureus. This information can be used for other clinical mastitis trials. The main advantage of inducing a subclinical mastitis instead of using naturally infected animals is that the first hours after infection can now be studied. This can be very important in the development of practical diagnostic tools for the detection of subclinical mastitis in goats.