may account for some of the differences shown. The oil vehicles and those with oil 
bases (water-in-oil emulsions and ointments) have the greatestability to retain penicillin 
in the udder. The direct relationship between the amount of penicillin used in intramam- 
mary infusion and the length of time it persists in the milk is also shown in figure l. 
Mineral or peanut oil, ointments, and water-in-oil emulsions are used almost 
exclusively as vehicles for penicillin and other antibiotics. Consequently, the maximal 
times that penicillin persisted in milk when suspended in these vehicles are shown for 
30 products in figure 2. Sixteen of the products caused persistence of penicillin in milk 
for no longer than 3 days, whereas penicillin persisted longer than 3 days when 14 of 
the products were used. 
Figure 3 shows the concentration of penicillininmilk 84 to 96 hours after intramam- 
mary infusion of these latter products. From 0.03 to 0.43 units of penicillin/ml. of milk 
were present in the first or second milking on the fourth day after infusion. Only three 
of the products shown in figure 3 were produced in this country while the others were 
produced in Europe. In addition, three of the products contained highly insoluble salts 
of penicillin (benzathine and N-benzyl-2 phenylethylamine), which are not used in this 
country for intramammary treatment. Nevertheless, sodium, potassium, and procaine 
salts of penicillin are used in this country as well as vehicles with mineral oil, peanut 
oil, and aluminum monostearate. Recent information on oil-base products made in this 
country show that levels of 0.05 to 0.10 u./ml. of milk were found 96 hours after infusion 
and traces as long as 132 hours (5-1/2 days) (lh 
One other factor, which must be considered when discarding milk from treated 
quarters, is that penicillin can also be excreted in the nontreated quarters. Ten cows 
demonstrated antibiotic residue in uninfused quarters for periods of 24 to 36 hours (1). 
After infusing one or more quarters, the highest concentration in any uninfused quarter 
was 0.05 u./ml. of milk. Negative results in untreated quarters were obtained, however, 
by Randall, et al (53) when one quarter was infused with 100,000 units of penicillin. 
Finally, there is no indication that repeated infusion of penicillin in the same quarter 
causes longer persistence in milk, although the data are very limited and more re- 
search on this problem is needed (37, 66, 68). 
Antibiotics other than penicillin--Figure 4 shows a comparison of the persistency 
of some of the principal antibiotics, other than penicillin, that are used for intramam- 
mary treatment of mastitis. Although the data are limited for some of the antibiotics, 
there is sufficient evidence to indicate that Aureomycin has the greatest tendency to 
persist in milk. In fact, it might be assumed that all of the doses in ointment lasted 
longer than 3 days. In the four instances where it lasts only 3 days (5,9,47,57) (repre- 
sented by two bars in the graph), testing was stopped at that time while the levels of 
antibiotic were still at the relatively high concentration of 1 to 6.2 Mg./ml. of milk. 
Terramycin and dihydrostreptomycin were also found in some instances to last 4 days. 
As in the case of penicillin, Aureomycin was found in the milk of untreated quarters 
after infusion of the treated quarters for 5 days (53), Terramycin for 1 day (53), and 
Neomycin for 4 hours (14). 
THE PARENTERAL INJECTION OF ANTIBIOTICS AND SULFONAMIDES 
' The treatment of mastitis with parenteral injections of antibiotics and sulfonamides 
is usually limited to acute cases. Contamination of market milk from such infections is 
no problem because the milk is usually discarded. However, dairy cattle are frequently 
injected with antibiotics and sulfonamides for the treatment of other diseases, and the 
milk is apparently normal and is used. Consequently, the farmer can inadvertently 
contaminate his milk supply by adding milk from these treated cows. To understand the 
problem better, we have summarized in figures 5, 6, and 7 the data on the persistence of 
various antibiotics and sulfonamides in milk after parenteral injection. 
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