RESIDUES IN MILK FROM ANTIBIOTICS USED IN MASTITIS TREATMENT 
Richard W. Brown! 
INTRODUCTION 
Mastitis is one of the most costly diseases of dairy cattle. During the last 30 years, 
many therapeutic agents have been used to treat mastitis. However, it was not until 
penicillin and other antibiotics became available that a new era of treatment was started, 
which has grown into big business on the premise that the use of antibiotics will cure 
the mastitis problem. It is estimated that 75 tons of antibiotics are used yearly for the 
treatment of mastitis in the United States (80). Today, about 35 companies prepare 
products for intramammary treatment. These products are distributed or sold under 
about 1,500 different labels. One pharmaceutical company estimated in 1957 that the 
dairy industry spends $15 to $20 million a year for these preparations and that at least 
80 percent of this business is in the form of over-the-counter sales to farmers. Un- 
doubtedly, antibiotics are valuable in treating mastitis when properly used; however, 
there is no indication that the incidence of this disease has been decreased through 
their promiscuous sale and use. Since the advent of these ‘‘wonder drugs,’’ the mastitis 
problem has not been solved, although their use has ‘‘cured’’ most interest in, support 
of, and ideas on fundamental mastitis research. 
The problems of antibiotic contamination of milk supplies have been adequately 
reviewed (12, 18, 20, 52). More than 10 years ago, antibiotics in milk became a problem 
to the cheese manufacturing industry (23, 32, 41). To overcome the effects of the anti- 
biotics, and particularly penicillin, increased inoculums of starter cultures were used, 
strains of bacteria resistant to increased concentrations of penicillin were developed, 
and penicillinase, an enzyme which destroys penicillin, was added to the milk (52). The 
cause for antibiotics in milk, that is, the widespread treatment of mastitis, was dis- 
regarded. Later, penicillin in milk was considered a potential public health problem 
because it might cause reactions in highly sensitive individuals (79). Only recently has 
it been shown that penicillin in dairy products can cause a chronic urticaria or dermatitis 
in sensitized persons (76, 83). 
According to surveys made by the Food and Drug Administration (F.D.A.), Depart- 
ment of Health, Education and Welfare, 11.6 percent of the milk samples tested in 1955 
contained residual penicillin; in 1956, this percentage was 5.9 (79, 80). Accordingly, 
certain steps taken by the F.D.A. in 1957 to alleviate the problem were: (1) The label 
on any antibiotic preparation intended for intramammary infusionwas required to contain 
a statement that the milk from dairy animals must not be used for human consumption 
within 72 hours after the last treatment for mastitis; (2) the amount of penicillin in any 
mastitis preparation used for intramammary infusion was limited to 100,000 units; 
(3) a cooperative program with the Department of Agriculture was started to educate 
the farmers of the importance of the problem (35). 
As a result of these measures, some progress was made in reducing the incidence 
of penicillin in market milk to 3.7 percent of samples tested in 1958 (35). Nevertheless, 
because of the failure to eliminate penicillin from market milk, the F.D.A. in 1959 
enforced an existing law that permits no detectable quantity of penicillin in interstate 
shipments of market milk. 
The amount of penicillin found in the milk samples tested during these surveys 
(35, 79, 80) ranged from 0.003 u./ml. to 1.2 u./ml., which would correspond to approxi- 
mately 3 to 1,000 units per quart of milk or less than 1 to 275 units per glass. These 
1Principal Research Veteranarian, Mastitis Research, National Animal Disease Laboratory, Animal Disease and Parasite 
Research Division, Agricultural Research Service, U, S, Department of Agriculture, 
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