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Determination of Milk and Mammary Tissue Concentrations of Ceftiofur After lntramammary and Intramuscular Therapy'
W.

E. OWENS, Z Y.

XIANG, C. H. RAY, and S. C. NICKERSON Hili Farm Research W o n Louisiana Agrlarltural Experiment Station Louisiana state University Agricultural Center Rt. 1, Box 10 Homer 71040

ABSTRACT

Twenty-five Sraphylococcus aurew strains isolated from bovine mastitis were

tested for their susceptibility to ceftiofur. Zone diameter for 30 pg disks averaged 39 nun, and minimum inhibitory concentrations ranged from .5 to 1 pg/ml. Tissue and milk concentrations were determined from biopsy and quarter milk samples collected from eight cows treated with either n i infusion o 100 or f 200 mg of ceftiofur, one or two intramuscular injections of 500 mg of ceftiofur, or combination therapy of n i infusion coupled with intramuscular injection. Three additional cows received two n i infusions of 200 mg of cephapirin at 24-h intervals. Intramuscular injections of ceftiofur resulted in tissue and milk concentrations below detectable limits. Sraphylococcus aureus was not eliminated f o infected mammary rm glands by infusion of 100 mg of ceftiofur or by injection of 500 mg of ceftiofur by 48 h after treatment. Combination therapy of 100 mg of ceftiofur infused and 500 mg injected reduced S. aureus numbers in milk and tissue markedly, as did infusion of 200 mg of ceftiofur. Cows receiving intramammary infusion of 200 mg of ceftiofur (two doses at 24-h intervals) had highest concentrations in milk (450 pg/ml at 4 and 6 h) and in tissue (.08 pg/mg at 30 h). These concentrations are similar to those obtained with two 2Wmg doses of

cephapirin a 24-h intervals. Histologic t analysis of mammary parenchymal tissues showed that combination therapy resulted in higher percentages of alveolar luminal area and lower percentages of interalvmlar stroma compared with infusion or injection alone. Histology of quarters receiving combination therapy was not