Interactions Between Nutrition and Immunity

Basic and applied research on the interactions between nutrition and the immune system has been a focal point for animal nutritionists for more than 50 yr. Economics and concerns about food safety and animal welfare shape the types of questions considered by researchers concerned with animal husbandry. As in human nutrition, a primary goal is to determine the impact of diet on the immune system and, consequently, the incidence of diseases controlled by, or caused by, the immune system. In modern agriculture, animals are almost always fed scientifically formulated diets that provide the required levels of nutrients at a minimal cost. Nutrient requirements set by the National Research Council and other organizations are based typically on levels that maximize growth rates and reproductive performance and prevent signs of deficiency. As in human nutrition, these standards are minimum requirements and rarely consider immunity or optimal health. Because optimizing animal health increases the wholesomeness of the human food supply and improves profits of animal producers, considerable research effort has been devoted to identifying nutrients that benefit the immune system when supplemented at levels above requirements. This research extends from basic laboratory-based experimentation at the mechanistic level to controlled field-based studies at the population level. Human nutritionists should be particularly interested in the results of these field studies because they offer a chance to look directly at the impact of highly controlled nutritional interventions on the resistance to infectious challenges in animals. Studies with poultry are particularly illuminating because diets differing in the level of only a single nutrient are fed to hundreds of thousands of birds living in very identical environments during the majority of their growth and development. These studies clearly demonstrate the dynamics of nutritional immunomodulation on the incidence of diseases at the population level. The first section of this chapter reviews the impact of specific nutrients on the immune system and the impact of these changes on the susceptibility of animals to infectious diseases.