Nutrition Intestinal Immunology
By: Dr. Caitlin Vonderohe
The interaction between nutrition and the immune system is a hot research topic in swine nutrition and physiology. In fact, a great deal of research in swine nutrition explores the links between the mucosal immune system and feed additives, feed ingredients, and feed composition.. Dr. Brooke Humphrey provided a practical perspective on a highly complicated and well-researched topic in his presentation “Linking intestinal immunity to applied approaches in pig nutrition” at the 14th Digestive Physiology of the Pig Symposium in Brisbane, Australia.
The pig is born with a fully functional innate immune system that includes barrier proteins, tight junction proteins, and antimicrobial peptides. However, the development of the more effective, and less inflammatory adaptive immune system can take several weeks. The interactions between the developing immune system and animal performance is partially determined by husbandry, nutrition and management.
Weaning is the most physiologically stressful point in a young pig’s life. Villus height decreases and the intestine becomes more permeable to gastrointestinal pathogens. Weaning pigs between two and four weeks of age can result a compromise of immune system development, increased mast cell activity, hyperactivity of the enteric nervous system and immune suppression. In fact, pigs weaned early are more susceptible to an E. coli challenge. However, because these changes are transient, there is a significant challenge relating these findings to an economic advantage for a producer.
Bacterial pathogens in the gut result are responsible for the greatest reductions in pig growth. Reductions in performance during enteric health challenges result from immune-mediated alterations in behavior to reduce feed intake, proteolysis in the muscle to support acute phase protein production in the liver and changes in bone density to support systemic mineral and protein requirements. A practical, and well-studied solution to this problem is to adjust the diet of pathogen-challenged pigs to provide additional amino acids to support the immune response, sparing muscle tissue.
Dr. Humphrey closed his presentation by focusing on three nutrients of interest to support the intestinal immune system around the time of weaning. Lipid digestion is highly limited immediately post weaning because the pig does not produce a sufficient amount of lipolytic enzymes. In fact, increased dietary fat inclusion results in reductions in feed intake. A practical solution to this challenge is to feed full fat ingredients (which may be more efficiently digested by young pigs) and reduce lipid inclusion in the diet.
Protein digestion is similarly limited in young pigs, particularly at weaning. If dietary protein is not digested by the pig, this protein travels to the hindgut where it can encourage the growth of potentially pathogenic bacteria, resulting in scours. It is important to consider standardized ileal digestibility of protein sources fed to young pigs to limit the amount of protein that reaches the hindgut.
Finally, weaning can result in a drop in serum levels of vitamin E, which can be further exacerbated by an E. coli infection. The addition of anti-oxidants can ameliorate inflammation from weaning, be protective against disease stress and result in improvements in growth performance.