USE OF INDUCED MAMMARY INFECTIONS FOR EVALUATING DRY COW TREATMENT PRODUCTS .1. DEVELOPMENT OF A METHOD

  • 1 January 1979
    • journal article
    • research article
    • Vol. 43  (4) , 426-429
Abstract
Experimental infections were induced by infusing 1 of 3 different numbers of colony forming units of Staphylococcus aureus strain 305 into 74 quarters of 17 cows at 30, 15 or 5 days before drying off. The remaining 26 served as controls. Of infused quarters, 73% were infected at drying off and calving, although some changes in status occurred during the dry period. All control quarters were negative at drying off, but 2, one in each of 2 lactations of the same cow, became infected during the dry period. There was no change in infection status during the dry period in 86.5% and 88.5%, respectively, of infused and control quarters. Disregarding dose size, 18/27, 19/24 and 17/23 quarters became infected following infusion at 5, 10 and 30 days before drying off. Disregarding time, significantly more infections (88%) followed infusion of a 10-4 dilution (mean count 3215 .+-. 182 SE) than with 10-5 and 10-6 dilutions combined (65%). A dose of S. aureus strain 305 consisting of 0.2 ml of a 10-4 dilution in sterile milk of a 6 h milk culture would provide optimum infection levels if no antibiotic treatment were given. Whether infusion took place 30, 15 or 5 days before drying off appeared immaterial.