SERUM INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) CONCENTRATIONS ARE INCREASED IN PIGS FED ANTIMICROBIALS

The effect of antimicrobial supplementation on the sera concentrations of IGF-I was determined in crossbred weanling pigs. Pigs were allotte d by weight, litter, and sex to either a control diet or a diet supple mented with ASP-250 (22.7 ppm of chlortetracycline, 22.7 ppm of sulfam ethazine, and 11.4 ppm of penicillin) for 5 wk. The diets contained 21 .8% crude protein and 1.15% lysine. Growth performance data were colle cted weekly. Insulin-like growth factor I and insulin-like growth fact or binding protein (IGFBP) analyses were performed on blood samples th at were drawn during the final week of the trial. Feeding ASP-250 to y oung pigs increased their sera IGF-I concentrations by 24.8% (P <.001) . A 59% increase in sera IGFBP-3 levels also was observed. The pigs fe d ASP-250 had a 26% increase in average daily gain (P <.01), a 6.7% im provement in gain:feed ratio (P <.05), and a 18.5% increase in feed co nsumption (P <.01) compared with pigs fed the control diet. Increased serum IGF-I concentrations with antimicrobial feeding may be involved in the enhanced growth performance observed.