Fermentation of Mastitic Milk from Antibiotic Treated Cows

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Abstract
Effects of antibiotics on the rate and extent of fermentation of mastitic milk were sought. Normal milk, colostrum, mastitic milk from cows not treated with antibiotics and mastitic milk samples from antibiotic treated cows (100,000 IU penicillin G and 150 mg neomycin sulfate/quarter each) were obtained from weigh jars during 3 consecutive morning milkings (4 cows/treatment), inoculated with a commercial lactic starter culture [containing Streptococcus cremoris and S. lactis] and fermented as individual-cow milkings. A drop in pH to 4.7 within 24 h was the indicator of satisfactory fermentation. Normal milk required 15 h, colostrum 49 h, untreated mastitic 29 h and treated mastitic 53 h to reach a pH of 4.7 when averaged across milkings. Because milking sequence seriously affected treated mastitic milk, fermentation samples were collected from 4 additional antibiotic-treated mastitic cows during the first 6 consecutive postantibiotic-treatment milkings and fermented as before. Postantibiotic treatment milkings 1, 2, 3, 4, 5 and 6 required 100, 73, 23, 17, 12 and 10 h, respectively, to reach a pH of 4.7. Antibiotic concentration in mastitic milk declined to permit satisfactory fermentation by the 3rd postantibiotic-treatment milking.

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