Influence of prepartum antibiotic therapy on intramammary infections in primigravid heifers during early lactation.

Jersey heifers were assigned alternately to three groups: 1) negative control (n = 41), 2) intramammary infusion of 200 mg of sodium cloxacillin (n = 38) at 7 d before expected parturition, and 3) intramammary infusion of 200 mg of cephapirin sodium (n = 36) at 7 d before expected parturition. The percentage of mammary glands infected prior to treatment was 62.2, 50.0, and 70.1 for groups 1, 2, and 3, respectively. The percentage of mammary glands infected during early lactation was 44.5, 8.6, and 2.1 for groups 1, 2, and 3, respectively. Most infections (87.1%) were due to Staphylococcus species other than Staphylococcus aureus. Thirty-six of 460 quarters were infected with major pathogens before treatment, 3 of 22 persisted following antibiotic treatment, and 9 of 14 persisted in the control group. Infusion of sodium cloxacillin resulted in antibiotic residues in 17.4% of samples obtained .5 d postpartum. All samples were negative at 3 and 10 d postpartum. Infusion of cephapirin sodium resulted in antibiotic residues in 84.7, 28.2, and 0% of samples obtained at .5, 3, and 10 d, respectively. Prepartum antibiotic therapy was effective in eliminating many IMI, especially those caused by coagulase-negative staphylococci, but there is the potential for antibiotic residues in milk.