Comparison of tilmicosin and cephapirin as therapeutics for Staphylococcusaureus mastitis at dry-off

Forty-four cows (26 Jerseys and 18 Holsteins) that had at least 1 mammary q uarter that was naturally (n = 12) or experimentally (n = 84) infected with Staphylococcus aureus were allotted to three treatment groups of approxima tely equal number at the end of lactation. Cows were dried off by abrupt ce ssation of milking, and dry cow therapy was administered as an intramammary infusion of cephapirin benzathine at 10 mi per quarter, an intramammary in fusion of tilmicosin (solution containing 300 mg/ml) at 5 mi per quarter, o r a subcutaneous injection of tilmicosin at 5 mg/kg of body weight on the d ay of drying off and another injection 4 d later. Mammary secretions were m onitored during the dry period and postpartum for antimicrobial residues, i ntramammary infection (IMI) status, and somatic cell counts. Results demons trated the following percentage cures for IMI caused by Staph. aureus at 28 d postcalving based on individual mammary quarters: cephapirin benzathine, 78.1%; tilmicosin infused, 74.2%; and tilmicosin injected, 9.1%. During th e first 4 wk after drying off, the mean concentration of tilmicosin in mamm ary secretions from cows infused with the antibiotic remained approximately 10-fold higher than that in secretions from cows injected with the antibio tic (3.43 vs. 0.32 ppm), and, by the time of calving, concentrations for co ws treated with both methods were below the dilution limit of the assay (<0 .1 ppm). Results demonstrated that intramammary infusion of tilmicosin was equally as effective as cephapirin benzathine in curing IMI caused by Staph , aureus at drying off; however, the subcutaneous injection of tilmicosin a t the dose used was not effective as a dry cow therapeutic against Staph. a ureus.