Early weaned pigs allotted either into “clean” or into “dirty” environmental conditions and potentially subject to high or low levels of antigen exposure, respectively, were used to determine the impact of 0, .67, 1.33, and 2% conjugated linoleic acid (CLA-60) on the immune status and growth performance. CLA levels modulate immune status in weanling pigs by decreasing the CD4 + :CD8 + ratio due to an increase in CD8 + and a decrease in CD4 + %. If the result of that ratio is favorable to the numerator, it means that the animal has a greater immune potential to fight against bacterial-type infections (serum antibodies produced by plasma cells) than against viral or other intracellular-type infections. The increase in CD8 + indicates a potential increase in cytotoxic T lymphocytes. These cells play an important role in the development of the response of the animal against viral infections. CLA caused an increase in alpha-1-acylglycoprotein (AGP), a serum acute-phase protein produced in the liver in response to stimulation from specific cytokines. No statistical significance in feed efficiency was attributed to CLA. Pigs placed into the clean environment utilized feed more efficiently than those placed in the dirty environment. Growth performance was shown to be independent of dietary treatments, but after a period of 42 days, pigs fed CLA become more viral immune competent than control animals
