Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy Science


Under the Food, Drug, and Cosmetic Act antibiotics are considered as ·adulterants in milk and milk products. Cultured dairy products cannot be made with milk containing small concentrations -of antibiotics. Also, minute quantities of antibiotics cause allergic reactions in some people. Penicillin is the most common antibiotic to which people are allergic, and penicillin is also the most commonly used antibiotic in the treatment of infections in bovines. Antibiotics, whether injected intravenously or intramuscularly, or infused into the udder of the cow, can be secreted into the milk. It is for this reason that withdrawal times for milk from cows treated with antibiotic preparations have been determined. The withdrawal time is that period following treatment with antibiotics for the antibiotic residue to be completely removed from the milk from treated cows. The method recommended by the Food and Drug Administration (FDA) for determination of penicillin concentration in milk is the Sarcina lutea cylinder plate method. Although penicillin is not the only drug used for treatment of infections, it is the antibiotic of choice when checking milk for drug residues. Therefore, tests for the detection of antibiotic residues in milk are usually rated on their sensitivity to penicillin. The two most commonly used methods for penicillin residues in milk are the Bacillus subtilis disc assay and the Sarcina lutea cylinder plate procedures. The ·cylinder plate method is more sensitive to penicillin than the disc assay method. Recently an antibiotic test has been developed which is reportedly more sensitive to penicillin than the disc assay or cylinder plate methods. It is marketed under the trade name of Delvotest P. One objective of this study was to determine whether the withdrawal time for milk from cows treated with penicillin would be increased if the Delvotest P method was used. Also, a comparison was made of relative sensitivities of the Delvotest P, disc assay, and cylinder plate tests for determination of penicillin in milk. Cows are sometimes treated in their dry period to prevent mastitis infections from developing. The "dry cow" antibiotic preparations have withdrawal times recommended by the manufacturer as do all the drugs used in treatment of infections in bovines. The withdrawal times for antibiotics used in dry cow treatments are determined from the time the cow calves. The manufacturer also recommends that dry cow antibiotic treatments not be used for a certain period of time prior to the ·expected calving date to insure that no antibiotics will be secreted longer than the recommended withdrawal time. Therefore, another objective of this study was to determine if antibiotics used in dry cow treatments persisted longer ·than the recommended withdrawal time in milk if the cows calved earlier than expected.

Library of Congress Subject Headings

Antibiotic residues
Milk contamination


Includes bibliographical references (pages 75-82)



Number of Pages



South Dakota State University


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Dairy Science Commons