Effect of dietary organic selenium on milk selenium concentration and antioxidant and immune status in midlactation dairy cows

• Dietary organic Se supplementation improved the antioxidant status of dairy cows compared with inorganic Se supplementation.
• Dietary organic Se supplementation increased the concentrations of selenium in whole blood and milk of dairy cows compared with inorganic Se supplementation.
• Dietary organic Se supplementation had no significant effect on milk performance of dairy cows compared with inorganic Se supplementation.
• Most immune measurements in serum of dairy cows were not affected by dietary Se source.

This study aimed to investigate the effects of the dietary selenium (Se) source on milk yield, milk Se concentration and antioxidant and immune status in dairy cows. Fourteen multiparous Holstein cows with similar dry matter intake (DMI), milk yield and parity were randomly divided into two groups with seven replicates in each group. The cows in both groups were fed basal diets supplemented with 0.3 mg Se/kg DM from sodium selenite or Se yeast, and the background Se level of the basal diet was 0.02 mg/kg DM. The experimental period lasted for 60 days. The results indicated that the DMI, milk yield and composition were not affected by the dietary Se source (P>0.10). During the entire experimental period, Se yeast supplementation significantly increased the serum glutathione peroxidase activity and decreased the malondialdehyde content (P=0.00) compared with selenite. The serum selenoprotein P content (30 d), thioredoxin reductase and catalase activities (60 d), and total antioxidant capacity (60 d) were also higher (P<0.05) with Se yeast supplementation than with selenite. Compared with selenite, organic Se supplementation increased the values of immunoglobulin (Ig) A and soluble CD4/soluble CD8 on day 30, soluble CD4 on day 60, and interleukin (IL)-1 during the trial (P<0.05). However, other measures of immunity, such as IgM, IgG, soluble CD8, IL-2, IL-4, IL-6 and tumour necrosis factor, were not affected by the dietary Se source (p>0.10). The total Se in the whole blood and milk were higher with Se yeast supplementation than selenite (P<0.05), and the milk Se concentration was increased markedly over the duration of Se supplementation from day 30 to 60. These results suggested that Se yeast may be more effective than sodium selenite in improving the antioxidant status and increasing the whole blood and milk Se concentrations of dairy cows.