The roles and subsequent requirements of Vitamin E and Selenium (Se) for cattle have been determined more from the reduction of disease states than from balance studies. Traditionally, nutrients were supplied to meet the minimal requirements for maintenance, growth, or prevention of classic nutrient deficiencies such as white muscle disease. The 1989 Dairy NRC recommends 0.3 ppm Se in diets for all cattle and 7 IU Vitamin E for adult cattle; 11-18 IU/lb for growing cattle. The 1984 NRC for beef cattle suggests 0.2 ppm Se and does not list a vitamin E requirement Veterinarians, however, can find recommendations that vary from the NRC. Selenium is unique as a nutrient in that the FDA limits supplemental Se to 0.3 ppm in a ration. This manuscript discusses what indications should create interest in Vitamin E or Se and how to determine supplemental amounts through evaluation of the animal, the feeds, and supplementation systems.
Vitamin E is a group of fat soluble vitamins called tocopherols that are found associated with lipids (cell membranes and adipose) in the body. It is transported in the plasma as a component of lipoproteins. Vitamin E functions as an antioxidant in cell membranes and thus protects the cell from oxidative damage. Several classic Vitamin E deficiencies include anemia (red cell damage), myopathies, and steatitis. Vitamin E is concentrated in colostrum and thus transferred to the vitamin E deplete calf. Vitamin E is not stored in a particular organ but can be passively stored in adipose tissue. Plasma Vitamin E has been used as a measure of Vitamin E status; adequate > 4.0 µg/ml marginal 2-4 µg/ml and deficient < 2.0 µg/ml.
Selenium is a trace element that is a component of several proteins, the most important is the enzyme Glutathione Peroxidase (GSH-Px). This enzyme acts as an antioxidant that inactivates peroxides. Most GSH-Px is found in water soluble compartments such as cellular cytoplasm or plasma. The classic Se deficiency is white muscle disease. Selenium is transferred from the dam to the fetus across the placenta and milk tends to be a poor source of Se. Selenium is not stored in a particular organ. Blood Se has been used as a measure of Se status; adequate> 100 µg/l, marginal 50-100 µg/l, and deficient < 50 µg/l.
The richest sources of Vitamin E are vegetable oils, cereal products that contain the oils, legumes, and in general, green plants. 1 Vitamin E content decreases in stored feeds especially feeds exposed to heat. The movement of dairy cows from pastures to dry lots probably decreased Vitamin E intake. Selenium content of feeds mirrors the Se content of the soils where the feed was grown, thus home grown feeds from Se-deficient regions tend to be Se-deficient. The increased use of by-product feeds and non-native feeds can change the relative Vitamin E I Se balance in a herd. In addition, analysis for Vitamin E in feeds is complex and few if any feed labs analyze feeds for Se.
Most veterinarians rarely find the classic vitamin E or Se deficiencies in cattle yet supplementation is still important for several factors. The first is that many of the vitamin and trace element requirements were determined on limited data generated prior to 1970. Cattle in present production systems generally perform at higher levels than their ancestors from 20-40 years ago. The need to increase nutrient requirements with increased production is common with protein and energy. A similar increase in trace elements and vitamins may also be needed.
The second factor is the concept of "neutraceuticals", i.e. that certain nutrients may have pharmacologic activities at a "dose" that is above what is considered a requirement Vitamin E supplementation at 500 IU/ day to steers increases the shelf live of meat and 1000-2000 IU/ day to lactating cows increases the stability of milk against oxidized flavor. These levels of Vitamin E potentially exceed the amount needed to maintain the animal, yet they produce a biologic effect on the product.
The third factor is the concept of "Conditional" nutrients, i.e. certain conditions (stress, other nutrients) can increase the requirements for nutrients. Vitamin E content may need to be increased as fat content of the diet is increased, especially if the fat does not contain Vitamin E or if the fats have oxidized (become rancid). Vitamin E supplementation has shown positive effects when supplemented to stressed cattle such as newly received feedlot cattle. In addition, Vitamin E has been used to reduce the rates of retained placenta and udder edema in dairy cattle.
The fourth factor is the role of Vitamin E and Se in immune function and thus the requirement for optimal immune function versus the requirement for maintenance and growth. Supplementation of Vitamin E and Se have reduced rates of mastitis and have enhanced humoral immune response.
Both Vitamin E and Se can be supplemented through the feed and by injection. A common injectable method is 10 ml of MU-SE®. Injectable Se in this form tends to be effective for days to weeks. Likewise, MU-SE® contains 50 IU of vitamin E I ml. Other injectable preparations of Vitamin E contain higher concentrations such as VITAL E(TM) 300 which contains 300 IU /ml and VITAL E(TM)500 which contains 500 IU /ml. In this authors opinion, injectable forms can be used when a deficiency is suspected or when supplementation in the feed is impossible. Supplementation in the feed at 0.3 ppm Se and 10-100 IU vitamin E/ kg feed are general recommendations.
Vitamin E and Se supplementation are still needed for many of our clients cattle. The need for Vitamin E supplementation increases as the intake of fresh green forages decreases. Selenium supplementation should be needed when the cattle are pastured on Se-deficient soils or fed feeds from these soils. Excessive vitamin E is a wasted expense as Vitamin E has a wide margin of safety. Selenium toxicosis, however, can occur and supplementation of Se above the FDA guidelines has legal ramifications.