On d 14 post-weaning, serum IGF-1 of pigs fed antibiotics was greater than pigs fed the control diet (p = 0.03), but no difference was observed between two organic acid treatments and control treatment. Moreover, serum IGF-1 on d 28 and urea nitrogen concentration on d 14 and 28 post-weaning were not affected by dietary treatments (p = 0.15) (Table 4).