The Effect of Antibiotics upon the Digestion of Feed Nutrients by Yearling Steers, with Bacteriological Data

Abstract

Two series of digestion and N-balance studies with 11 steers showed that Aureomycin from Aurofac 2A (Lederle) fed at the rate of 32 or 100 mg/day caused a decrease in digestibility of feed nutrients. Thirty-two, 100 or 400 mg of penicillin from Antibiotic Feed Supplement (Merck) (0.2 g of penicillin /g of supplement) had no effect on the digestibility of the nutrients. Both Aureomycin and penicillin at all levels caused a highly significant (P = 0.01) decrease in N retention. Penicillin at 100 mg level did not upset the rumen flora and environment Aureomycin (100 mg) caused a less desirable rumen flora and a decreased ability to digest fiber in the miniature artificial rumen.