Duration of Antibiotic Residues in Milk from Cows Treated via Intrauterine and Intramammary Infusion

Antibiotics have been employed by farmers and veterinarians for treatment of infectious cattle diseases for over 3 decades. The most common of these diseases in dairy cows is mastitis. Mastitis is defined by the National Mastitis Council (NMC) (49) as an inflammation of the mammary gland. It is the most prevalent and most costly disease .of dairy cattle. It is estimated that at least 50% of all cows are infected with some form of mastitis at any one time in one or more quarters; cows in the average herd contract clinical mastitis one and one-half times per yr (49) which results in economic loss. According to the NMC, the average estimated total mastitis cost per cow per year is $161.00. Penicillin alone or combined with other drugs has become the product of choice for treating many forms of infectious mastitis in the bovine. An estimated number of antibiotic treatments per case of mastitis is two (49). Therefore, using the NMC estimates and assuming 10 million cows in the United States, this places the total number of treatments in the United States at 30 million per year. In South Dakota, the estimated number of treatments is about 510,000 (49). With this level of use, the chance of penicillin or any other antibiotic contaminated milk reaching the market place exists. Antibiotics, whether infused into the udder or injected intramuscularly, or intravenously, and more recently infused into the uterus, are secreted into the milk. The length of time needed for the antibiotic residue to be .completely absent from the milk fol-lowing treatment is called withdrawal time. Withdrawal times from cows treated with antibiotic preparations have been determined and are listed on labels of most preparations. Milk and milk products containing antibiotic residues are considered adulterated under the Food, Drug and Cosmetic Act of 1938. The Food and Drug Administration (FDA) has established a zero tolerance level of antibiotics in milk. Such products may present a significant hazard to health since small concentrations of antibiotics cause allergic reactions in some people and sensitivity reaction to antibiotics in others. Certain bacteria may develop resistance to antibiotics and become resistant to such treatment. Also, cultured products are difficult or impossible to make from milk containing antibiotic residues. The Bacillus subtilis overnight disc assay method remains as the method of choice for monitoring antibiotic residues in producers\u27 raw milk. The FDA recommends the Sarcina lutea cylinder plate method for determination of penicillin concentration in dry milk. The cylinder plate method is more sensitive to penicillin than the disc assay method (52) but takes 16 to 18 h to run. There is a need for a rapid method to assist the milk industry and milk regulatory agencies in detecting any level of antibiotics. There are new tests that have been developed recently which are simple, quick, and more sensitive. These tests are the Difco disc assay using Bacillus stearothermophilus, the agar diffusion .test which uses Bacillus stearothermophilus var calidolactis, and an enzyme immunoassay technique known as the Charm test. One objective of this study was to measure the duration of antibiotics in milk from cows treated for uterine infections. Determinations for antibiotics were made by disc assay and the Charm test. Another objective was to compare the relative sensitivity between the Difeo disc assay, the Charm test, and the disc assay for determination of penicillin in milk from cows treated via intramammary infusion