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The Effect of High Level Antibiotic Supplementation during Part or All of the Growing-Fattening Period of Swine¹

South Dakota Agricultural Experiment Station, Brookings

Abstract

In one trial 60 weanling pigs were fed in 10 replicated lots to study the value of 3 different levels (25, 50 and 100 gm. per ton) of a penicillin-streptomycin mixture and the value of a high level (100 gm. per ton) of chlortetracycline when added to a mixed ration. The addition of the antibiotics produced a highly significant (P<0.01) increase in rate of gain. There was very little difference in the rate of gain of the pigs fed the different levels of penicillin-streptomycin. The pigs fed the two higher levels of penicillin-streptomycin required 5% less feed than the control group.

Two trials were conducted to compare the value of high and low level antibiotic supplementation and to determine the feasibility of withdrawing or reducing the high level supplementation at a weight of approximately 100 lb.

In the one trial involving chlortetracycline there was a significant increase in rate of gain from all antibiotic treatments. The high level of chlortetracycline 100 gm. per ton resulted in consistently faster gains than 10 gm. per ton during the early growth period. Withdrawing or reducing the high level to 10 gm. per ton at 100 lb. had a depressing effect on feed intake and daily gains during the period from 100 to 200 lb.

Pigs fed penicillin-streptomycin gained faster than control pigs but the differences were not significant at the 5% level. Supplementation with a high level of penicillin-streptomycin resulted in consistently faster rates of gain than the low level of this antibiotic during the early growth period as was true for chlortetracycline. Gains were reduced when penicillin-streptomycin was removed at 100 lb. but not when it was reduced to 10 gm. per ton. The high level of penicillin-streptomycin increased feed efficiency 7% over the control group.

¹ Contribution from the Department of Animal Husbandry and approved for publication by the Director of the Agricultural Experiment Station as Publication No. 347 of the Journal Series.

² Grateful acknowledgement is made to American Cyanamid Co., Pearl River, N. Y.; Chas. Pfizer & Co., Inc., Brooklyn, N. Y.; and Merck & Co., Inc., Rahway, N. J., for funds or products which made this investigation possible.