Effect on Subsequent Feedlot Performance of Rotating or Withdrawing Dietary Antibiotics from Swine Growing and Finishing Rations

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Abstract
Four feeding trials were conducted to evaluate two antibiotics and copper in several rotational schemes and to determine the effect on subsequent performance of withdrawing supplemental antibiotics when pigs weighed 75 lb (34 kg) and 150 lb (68 kg). A total of 507 crossbred pigs averaging 18 lb (8 kg) to 75 lb (34 kg) initially were self-fed to a market weight of about 207 lb (94 kg). During the first phase of all trials, average daily gain was improved about 11% when the young pigs were fed rations containing antibiotics. This improvement resulted primarily from an increase in feed intake. In three of the four trials, the overall feedlot performance (average daily gain, feed intake and feed efficiency) was not different between control pigs and pigs supplemented with antibiotics, whether the antibiotic was fed continuously to market weights or withdrawn at 75 lb (34 kg) or 150 lb (68 kg). In trial 3, the initial improvement in average daily gain and feed intake obtained during the early part of the trial was maintained through the finishing phase resulting in an overall small improvement; however, feed efficiency was not improved. No advantage from the rotation of antibiotics and copper and little or no advantage from dietary antibiotics after 75 lb (34 kg) in body weight was observed. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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