Efficacy of a Broad Spectrum Antibiotic Versus Clinical and Subclinical Bovine Mastitis

Abstract

Efficacy of a broad-spectrum antibiotic effective against gram-positive and gram-negative bacteria was investigated as an experimental drug for treatment of mastitis caused by S aureus, Staph spp., Strep spp., and E. coli. Ten commercial dairy farms with a total of 861 cows (73 Jerseys, 788 Holsteins) with various herd sizes and types of cow housing participated. 305 day mean actual milk production ranged from 11,000 to 23,600 pounds (4994 to 10,714 kg), and mean bulk tank SCC for 6 months ranged from 130,000/ml to 815,000 on the farms. Treatments used were experimental treatment, 750 mg, or control treatment, 200 mg of cloxacillin, administered by intramammary infusion in a double blind study. Criteria for cure involved repeated reculturing of milk over 28 days combined with somatic cell count data.

Clinical mastitis was detected in 119 quarters, 34 of which were removed from the study because additional treatment was required, or the cows were sold or died. 85 clinical mastisis cases remained which met the required case definition and protocol: 8 Strep ag, 23 S aureus, 25 Strep sp., 4 Staph sp., 1 lE coli, 5 Klebsiella, and 9 Others. There were 71 cases of subclinical mastitis, 31 caused byS aureus, 10 caused by Strep sp., 29 caused by Staph sp., and one caused by Klebsiella.

Significant differences between the experimantal drug and cloxacillin in efficacy and overall cure rates for mastitis will be discussed in this presentation.