An experiment which utilized 17 weeks of production was designed to examine the response of weanling pigs to diet complexity.  Piglets were divided at weaning (28 days) into heavy or light body weights and fed either a simple diet for 14 days or a complex diet for 1 or 4 days, followed by the simple diet. Feeding the complex diet for 4 days improved growth performance for the first week following weaning when compared to feeding it for 0 or 1 day. Pigs which were lighter at birth, lost less body weight at weaning, and showed a greater positive response to the complex diet than heavier birth-weight pigs. Phase 1 diet could be used more efficiently and cost effectively by targeting it specifically to the lighter pigs at weaning.