The Importance of Vitamin E and Selenium

Vitamin E and selenium perform important functions in the cow. Deficiencies of one, or both, of these nutrients have been implicated in white muscle disease, retained placentas, oxidized milk, lower immune function and mastitis.

The roles of these two nutrients are closely related. Both selenium and vitamin E protect cells from the detrimental effects of oxidation but they do so in different ways. Vitamin E, an antioxidant present in the cell membrane, prevents the formation of harmful free radicals. Selenium functions throughout the cell to destroy peroxides, another harmful compound. This explains why selenium will correct some deficiency symptoms of vitamin E and not others. Although feeding large amounts of selenium does reduce the need for vitamin E and vice versa, high levels of one nutrient does not eliminate the need for the other.

Current Agriculture and AgriFood Canada regulations allow diets to be supplemented with up to 0.3 mg/kg supplemental selenium. This equates to 6 to 8 mg/day for lactating cows. Dry cow diets are also limited to 0.3 mg/kg, which corresponds to about 3 mg per day. This may be insufficient for dry cows fed feedstuffs grown in selenium deficient areas. Selenium levels in commercial feeds can be increased with a veterinary prescription. Although selenium is a necessary nutrient it can also be toxic at fairly low levels. It is important that only one source of supplemental selenium is provided and that care be taken to avoid toxicity.

Information from clinical and field studies indicate that vitamin E recommendations from NRC do not promote optimum udder health. Green forages are good sources of vitamin E, however, the vitamin E content of feedstuffs decreases during drying and storage. Current industry recommendations for cows receiving stored forage are 500-600 IU of supplemental vitamin E/day for milking cows and 1000 IU/day for dry cows.

Although mineral mixes do contain some vitamin E, the levels are usually very low (40-500 IU/kg). Some mineral mixes do contain elevated levels of vitamin E (1500 IU/kg) but at normal levels of intake still do not provide sufficient vitamin E. Feeding 13 g of a vitamin E premix with 40,000 IU/kg will provide milking cows with 520 IU of supplemental vitamin E per day.

Selenium and vitamin E can also be injected. A vitamin E-selenium injection can be given 21 days prior to calving to boost circulating blood levels when problems persist.