Two experiments were conducted in order to evaluate spray dried animal plasma (SDAP) as an alternative to antimicrobial prophylactic medication with colistin in weaned pigs. Experiment 1 was conducted with 96 piglets (21-day-old) and Experiment 2 was conducted with 128 piglets, (64 weaned at 22 days of age and 64 at 32 days of age). In both experiments the effects of the use of SDAP and/or colistin were compared. Four dietary treatments were used in a factorial arrangement: negative control (N), diet containing SDAP (P), diet containing colistin (C) and diet containing both SDAP and colistin (PC). SDAP was added to diets P and PC at 50gkg - 1 between days 0-14 of the trial and at 20gkg - 1 from day 15 to the end of the trial. In Experiment 1, SDAP improved average daily gain (ADG; +42g per day; P<0.05) and feed conversion ratio (FCR; -0.13; P<0.01) between days 0-14, and FCR (-0.03; P<0.05) between days 0-35 compared to the diets without SDAP. Colistin improved FCR between days 0-14 and 0-35 (-0.13; P<0.05 and -0.05; P<0.01, respectively) compared to the diets without colistin. No significant effects (P>0.05) were observed between days 15-35. No interaction between SDAP and colistin was found, suggesting that their modes of action are independent. In Experiment 2, SDAP improved FCR between days 0-14 and 0-28 (-0.05; P=0.08 and -0.05; P<0.05, respectively) with respect to the diets without SDAP. No significant effect (P>0.05) of colistin for any of the parameters studied was detected in any of the experimental periods. FCR, however, was only improved in the older pigs between days 0-28 post-weaning (-0.03; P<0.05). No significant interactions between SDAP, colistin and age at weaning were observed with any parameter (P>0.05). It is concluded that SDAP may be a good alternative to medication with colistin as both products gave similar improvements in performance. The positive effects of SDAP and colistin were more important during the first 2 weeks post-weaning and appeared to be higher in pigs weaned at a younger age, although no significant interaction between age at weaning and SDAP or colistin was observed.