Date Full Report Received


Date Abstract Report Received



Primary Investigator:

A study was conducted to evaluate the use of growth promoting antibiotics on growth performance of gilts (n=200) in the nursery and finishing phases, the economics of using growth  promoting antibiotics and the development of antibiotic resistance. Pigs fed antibiotics in the nursery had increased ADG, ADFI, and GF one week after weaning compared to pigs fed no antibiotics. No improvements in growth were found during the remainder of the nursery phase, or during the finishing phase. Resistance of commensal bacteria to chlortetracycline and virginiamycin increased from week 1 to 5 of the nursery for all pigs. Resistance decreased from week 5 to 9 when the antibiotic growth promoter was switched, however increased from week 9 to the end of the trial. Commensal bacteria isolated from groundwater sampled from simulated water runoff events at the end of the nursery and finishing phases showed similar resistance patterns to that of fecal bacteria. Economic analysis based on weight gain, mortality, and feed consumption during the trials showed that relatively small differences in performance can produce economically important differences in cost of production. The group of pigs that received growth promoting antibiotics in the nursery and none in the finishing phase had calculated costs that were $4 or more per head lower than the other groups in this experiment. The lack of statistical significance of differences in performance measures precludes statistically significant differences in calculated costs. Use of antibiotic growth promoters may not be beneficial in clean, isolated facilities with high labor inputs. Antibiotic resistant bacteria can develop and  proliferate regardless of the usage of antibiotic growth promoters.