Prevalence of mastitis in dairy heifers and effectiveness of antibiotic therapy

Dairy heifers were treated 0 to 90 d, 90 to 180 d, or 180 to 270 d prepartu m with one of five different antibiotic products to determine the best time and with which product they should be treated prior to calving. Two hundre d thirty-three heifers were included in the study. At the initial sampling, 56.5% of quarters were infected with some type of organism and 15.4% of qu arters were infected with Staphylococcus aureus. Treatments included a ceph apirin dry cow product, a penicillin-novobiocin dry cow product, a penicill in-streptomycin dry cow product, an experimental dry cow product containing tilmicosin, and a cephalonium dry cow product not available in the United States. Cure rates for the five antibiotic products indicated that all were equally effective against Staph. aureus and all were significantly more ef fective than the spontaneous cure rate observed in untreated control quarte rs. No differences in efficacy were observed due to the different treatment times prepartum. However, fewer new Staph. aureus infections occurred afte r treatment in the group treated at 180 to 270 d prepartum, indicating that treatment in the third trimester will reduce the chances of new intramamma ry infections occurring after treatment and persisting to calving.