PENICILLIN-G AND PENICILLIN-G TINIDAZOLE TREATMENT OF EXPERIMENTALLY-INDUCED SUMMER MASTITIS - EFFECT ON ELIMINATION RATES OF BACTERIA AND OUTCOME OF THE DISEASE

Two udder hind quarters of ten pregnant heifers were inoculated experi mentally with a combination of Actinomyces pyogenes, Peptostreptococcu s indolicus and Fusobacterium necrophorum at a dose of 9X10(8) colony forming units (CFU) of each species of bacteria. The development of ae robic-anaerobic mastitis was followed-up clinically and through analys is of udder secretion samples. All heifers developed acute clinical ma stitis. Thick, purulent secretions with foul odour were already presen t 24 h after infusion. At 32 h post inoculation, 19 of 20 quarters har boured all infused bacteria, the viable counts of bacteria varying fro m 10(4) to 10(5) CFU/ml. No bacteria were isolated from blood samples taken simultaneously. NAGase values of udder secretions, indicating ti ssue damage, were high. The heifers were treated systemically with pen icillin G alone, or in combination with tinidazole. Treatment started 32 h after inoculation acid was continued for three days. The anaerobi c bacteria (F. necrophorum and P. indolicus) were usually eliminated w ithin four days, while A. pyogenes infections often persisted in the q uarters. Penicillin G with tinidazole was not more effective than peni cillin G alone: of the four heifers which recovered from infection, tw o were treated with penicillin G alone and two with the drug combinati on. The most important factor affecting the recovery seemed to be the host response of individual heifers. The six heifers which did not rec over from the infection were continuously infected after calving, harb ouring A. pyogenes in ten quarters, and P. indolicus and F. necrophoru m each in three quarters.