A microbiological assay of penicillin in animal feeds.

The universal acceptance of the animal growth-promoting properties of some antibiotics and their wide usage in formulated commercial feeds requires that simple, rapid and reliable analytical methods be available for control purposes. Of the several antibiotics used in poultry rations, penicillin exerts its growth-promoting properties at levels considerably lower than other antibiotics (2 grams penicillin per ton), and thus, the analytical problems are accentuated. For penicillincontaining feeds, two problems are presented (a) a method of preparing stable extract from feed samples and (b) a method of measuring quantitatively the small amount of penicillin in the extract. From the voluminous information available on the properties of penicillin, it is well known that the antibiotic is incompatible with many solvents. In this report, only two salts of penicillin are considered, procaine and dibenzyl ethylene diamine (DBED), since these are the only forms currently employed in commercial feeds.