Reduced growth and less efficient use of nutrients is found in sub-clinical disease. Health and nutrient requirements need to be better understood now that in-feed antibiotics have been eliminated. The efficiency of utilization of dietary threonine for growth in pigs decreases when feedstuffs have high-fibre. Threonine is important to mucin production and it is a precursor for the synthesis of many acute proteins involved in the immune response. An increased threonine requirement is needed with increased fibre diets and immune challenge in growing pigs. There was not a further increase in the requirement from the interaction of the two variables. Dietary factors and stressor interactions need to be known so that nutrients meet their proper requirements and animal health and productivity can be enhanced.