The Effects of Early Antibiotic Treatment Following Diagnosis of Mastitis Detected by a Change in the Electrical Conductivity of Milk

Mastitis was induced experimentally by infusion of Streptococcus uberis or Staphylococcus aureus into the mammary glands of lactating dairy cows. Clinical mastitis was identified when clots appeared in foremilk (conventional diagnosis) or was predicted by changes in the electrical conductivity of foremilk (early diagnosis). The responses to intramammary antibiotic treatment that was initiated after early diagnosis of mastitis and after conventional diagnosis were compared. Early treatment significantly limited the severity of the disease and, in many cases, prevented the appearance of any visible signs of infection. Milk yield was less depressed, and the somatic cell count (SCC) was lower, when treatment was initiated earlier. The SCC of the quarter at the time mastitis was predicted was approximately 2 × 106 cells/ml for both pathogens, which was significantly less than when clots appeared at conventional diagnosis, approximately 4 × 106 and 12 × 106 cells/ml for Staph. aureus and Strep. uberis, respectively. The time required for SCC to recover to