ANTIBIOTIC RESIDUES AND PREVALENCE OF MASTITIS PATHOGEN ISOLATION IN HEIFERS DURING EARLY LACTATION FOLLOWING PREPARTUM ANTIBIOTIC-THERAPY

The present study was conducted to determine if antibiotic treatment o f heifer mammary glands earlier in the prepartum period reduced the oc currence of residues in milk without compromising efficacy in treatmen t of intramammary infections. Heifers were assigned randomly to tao gr oups: 1. untreated negative control (n = 42); and 2. intramammary infu sion of 200 mg cephapirin sodium (n = 40) 14 days prior to expected ca lving. Mammary secretions were collected before treatment and during e arly lactation, and were analyzed for residues by the Bacillus stearot hermophilus disc assay. Only four of 127 samples (3.1%) obtained from cephapirin-treated mammary glands at 3 days after calving were positiv e for residues and most (three of four) were from a heifer that calved within 3 days of treatment Mammary secretions were also collected bef ore treatment, and at 3 and 30 days after calving for microbiological evaluation. For untreated control heifers, mastitis pathogens were iso lated from 67.3% of samples obtained from mammary glands 14 days prior to expected calving, 55.6% obtained 3 days after calving and 36.4% of samples obtained 30 days postpartum. A similar percentage of samples (63.8%) was positive for mastitis pathogens at 14 days before expected calving prior to antibiotic treatment. However, only 15.1% of samples obtained at 3 days after calving and 7.9% of samples obtained 30 days postpartum from mammary glands of antibiotic-treated heifers containe d mastitis pathogens. Coagulase-negative staphylococci were isolated m ost frequently. Intramammary infusion of antibiotics earlier in the pr eparturn period markedly reduced the occurrence of residues in milk du ring early lactation without affecting efficacy.