The major impact of vitamin E on immunity appears to relate to enhanced neutrophil function. Oral or parenteral administration of vitamin E in periparturient dairy cows generally has not affected neutrophil phagocytic activity but has improved the ability of blood neutrophils to kill ingested bacteria. Supplementa- tion of 3000 IU of vitamin E/day during the transition per- iod prevented a decline in neutrophil superoxide anion production and interleukin 1 (IL-1) production after partu- rition compared with control cows not supplemented with vitamin E. Rapid recruitment of neu- trophils is critical for maximizing host defense mechanisms. Vitamin E supplementation at 3000 IU/day prevented a decrease in chemotactic responsiveness of neutrophils beginning at 2 weeks prior to and continuing for 4 weeks after parturition. Limited research sug- gests that vitamin E may enhance chemotaxis by increasing receptor-bound urokinase–plasminogen activator in neu- trophils.
Production of IL-1 and major histocompatibility (MHC) class II antigen expression by blood monocytes were improved by vitamin E supplementation. However, measures of mammary macrophage function have not been affected by vitamin E in peripartu- rient cows. Vitamin E supple- mentation during the transition period also did not affect lymphocyte blastogenic responses to stimulation with con- canavalin A (Con A), a T-cell mitogen.