Quality of starter diets appears to have no overall effect on growth performance after nursery exit, but it can impact the immune response. Pigs in this study were fed a low or high protein starter diet with supplemented fish or corn oil, and vaccinated with different antigens. Blood samples were taken 14 and 28 days later to determine the immune response. The supplementation of fish oil lowered the immune response as shown by a lowered IgG1, IgG2, local skin fold thickness, and haptoglobin. The complexity (level of protein) of the diet did not affect the immune response.