Effects of prepartum evaporative cooling and vitamin E supplementation on immune function of Holstein cows during summer in Florida
Objective was to evaluate the relationship of vitamin E (VitE) supplementation and prepartum environment on immunity of Holstein cows. Animals (n=70) were blocked at 30 d prepartum by parity, milk yield, and body weight, and randomly assigned to treatments arranged in a 2 x 2 factorial. Cows were housed until parturition in either a free-stall barn equipped with fans and sprinklers (Cooling - C) or in an open lot providing only shade (No cooling - NC). After parturition, all cows were housed in a free-stall barn equipped with fans and sprinklers. All-rac-alpha-tocopherol (DSM, Parsippany, NJ) was top dressed daily at 1000 IU prepartum and 500 IU postpartum per cow for moderate VitE (M) or 3000 IU prepartum and 2000 IU postpartum per cow for high VitE (H). Blood samples were collected in the prepartum at days -30, and -14 relative to parturition. After calving, blood samples were obtained at days 3, 7, 14, 21, 28, 35 and 42. Analyses included phagocytosis and oxidative burst by neutrophils, percentage of lymphocytes positive for IL-10 and IFN-γ production after PMA/ionomycin stimulation, percentage of total, CD4(+), CD8(+), and γδ subtypes of T lymphocytes, concentrations of serum IgG against ovalbumin challenge at days -30, -14, and 3, and acute phase proteins. Data were analyzed by ANOVA for repeated measures with PROC GLIMMIX of SAS. Non-normally distributed data was appropriately transformed. Results from cytokines and neutrophil function analyses are presented as fold increase in percentage of positive cells or mean fluorescence intensity (MFI) relative to unstimulated controls. Feeding more VitE increased (P<0.05) the percentage of lymphocytes producing IFN-γ (10.0 vs. 5.4). Prepartum cooling tended (P<0.10) to increase the percentage of T lymphocytes (31.0 vs. 23.4%) relative to total lymphocytes, CD4(+) subtype (12.4 vs. 7.4%), and IgG against ovalbumin (0.552 vs. 0.480 O.D.). Providing H vitE to NC cows tended to increase phagocytic activity (MFI) by neutrophils (4.83 vs. 4.25) whereas the reverse occurred when cows were cooled prepartum (4.52 vs. 5.20). Oxidative burst activity (MFI) of neutrophils from multiparous cows was enhanced when cows were cooled (8.72 vs. 6.59) whereas the opposite occurred for primiparous cows (4.84 vs. 5.84). VitE supplementation and prepartum cooling caused changes in adaptive immunity patterns. Additionally, prepartum cooling provided a conditional improvement of innate immunity depending upon amount of vitE supplemented and parity, which might reflect differences in metabolic and oxidative stress status.
Keywords: cow, heat stress, vitamin E