Impact of immune system activation on the rate, efficiency, and composition of growth, the efficiency of nutrient utilization and lysine needs of growing pigs
Two experiments were conducted to determine the impact of immune system (IS) activation on the rate, efficiency, and composition of growth, efficiency of nutrient utilization, and lysine needs of growing pigs. The use of a medicated early weaning scheme resulted in elimination of pathogenic antigens present in the herd of origin of pigs as measured by serological evaluation of prevalent antigens. This decrease in pathogenic antigen level resulted in a decreased level of IS activation as defined by the criteria of decreased CD:CD ratio and decreased serum alpha-1 acylglycoprotein concentrations. The differences in both CD4:CD8 ratio and serum alpha-1 acylglycoprotein were evident throughout the stages of pig development evaluated in this study, indicating that chronic differences in IS activation existed and were persistent throughout the duration of pig development. Minimizing activation of the immune system via minimizing pathogenic antigen exposure resulted in increased (P .15) the partial efficiency of L utilization for proteinaceous tissue deposition, the partial efficiencies of energy utilization for protein or fat deposition, or daily maintenance needs. Due to the increase in proteinaceous tissue growth, minimizing IS activation increased dietary L needs by.15 to.30% and daily L needs by 2 to 6 grams per day and these effects were consistent throughout pig development. Thus, minimizing IS activation via management schemes increases proteinaceous tissue growth and due to this enhanced rate of growth, increases lysine needs (% and grams/day).