Among the vast number of livestock producers in the United States, few may understand the importance of Selenium (Se) in animal nutrition. This micronutrient, needed in miniscule quantities, is a dietary requirement for most animal species.
Curiously, Se has been believed toxic longer than any other essential mineral. In 1857, cavalry horses at Fort Randall, S.D., were believed to have experienced some of the first cases of Se toxicity in the United States. These horses experienced losses of manes and tails along with the sloughing of their hooves. Nearby, settlers also noticed these symptoms in their livestock. The people began calling this “alkali disease” because they believed there was an association of these symptoms with the alkaline steeps, a common watering source. Selenium was officially declared hazardous in 1934. It was not until 1957 that Se was found to have useful benefits by scientists.
In 1957, Se was discovered to protect young ruminants from white muscle disease. White muscle disease, otherwise known as nutritional muscular dystrophy, predominantly occurs in young ruminants born to Se deficient mothers and if not treated, can cause death of the offspring within a few days after birth.
Selenium can be found throughout most of the soils in the United States. Three factors determine the amount of Se forages contain; the species of plants and forages, the chemical form of the Se in the soil and the amount of Se in the soil.
Evaluating your feed and pasture nutrient contents can be beneficial in determining if your cattle are receiving adequate amounts of Se. In dry lot feeding circumstances, Se deficiencies can limit cattle’s maximum performance. Infertility can also result in ewes that are grazed on pastures containing Se deficient soils.
Identifying Se deficiencies is often difficult to determine in mature cattle since symptoms are unapparent. The biggest indication lies within the cow’s calves when they show sign of white muscle disease or even impaired immunities. The calves can get sick more often.
Vitamins and minerals essential to livestock, as well as to humans, have complex interrelationships. Evidence has found that such a relationship exists with Se, Vitamin-E (Vit-E), lipids (fats), sulfur and sulfur containing amino acids (proteins). If one of these nutrients is altered, the requirement of another nutrient may change. Together Se and Vit-E work as valuable antioxidants removing toxins from the body. Selenium has also been found to attach to some proteins as they are absorbed. Without Se, animals may not have the ability to absorb certain proteins.
In equine animals, Se plays important roles ranging from antioxidants to growth contributors. As in other species, Se deficiencies can cause stunted growth and white muscle disease in younger horses and reproductive problems in broodmares. In stallions, antioxidant supplements (Se and Vit-E) have been found to improve semen quality.
Besides serving the role of antioxidants, Se and Vit-E play an important role in the immune system. Immune systems can become impaired when animals become deficient in vitamins and minerals. In dairy cattle, Se and Vit-E deficiencies are found to increase mastitis infection. Vit-E deficiencies increase the risk of obtaining the infection, while Se prolongs its healing process. Together they can help to prevent mastitis. One study, performed by Larry Smith from Ohio State University in 1984, found the percentage of mastitis was reduced by 46 percent when Holstein dairy cows were supplemented with Se alone, 44 percent with Vit-E and 62 percent when both nutrients were combined. The duration of mastitis was shortened by 27 percent with Se, 14 percent with Vit-E and 42 percent with both supplements. Dairy cattle frequently experience these nutrient deficiencies as the majority of them are fed ensiled forages. Generally, these forages tend to have 1/5 to 1/6 the amount of nutrients that are found in fresh forages. Having a nutrient analysis performed on silage will be the best indicator of its nutritional value as it varies among different forages and geographical locations.
Micronutrients are truly important to animal health; however they are needed in miniscule quantities. Too much of a good thing can be harmful. A case of acute Se toxicity, which implies that the toxicity occurs quickly, can cause a garlic smell to the breath, vomiting, shortness of breath, muscle spasms, and even death as the result of respiratory failure.
Another toxicity concern of Se is blind staggers, which can result when a toxic level of Se is obtained over several days. In general, a level of as little as 0.5 ppm (parts per million) is required for Se toxicities to occur. However, Se is useful. In a Canadian experiment, sub-toxic levels of Se were administered to a group of sheep. These sheep displayed increased wool fiber thickness, which in turn increased the total weight of the fleece.
Because toxicity complications can occur with excessive Se, there are many controversies over the legality of Se supplements. The first Se supplements were approved for the use of swine and chickens in 1974, in the quantities of 0.1 ppm. At this time, turkeys were also approved for Se supplementation but in amounts of 0.2 ppm. One major contributor to this approval, besides the nutritional benefits, was the discovery that the swine and poultry industry combined annually lost $82 million from Se-related problems. In 1957, dairy and beef cattleman, as well as some sheep farmers, petitioned the FDA for the ability to provide Se in a supplement to their animals. Lack of supplementation was costing them an estimated $545 million annually. The FDA granted the farmers’ request in 1978 at 0.1 ppm levels which were later intensified in 1987 to 0.3 ppm for all farm animals.
There are two forms of Se supplements, sodium selenite and sodium selenate. Of the two, sodium selenate is better utilized because the body can more easily break it down to Se. Selenium can be administered orally or through an injection; however, you should always consult your veterinarian when considering Se injection supplements. If your feeding program requires Se supplements, you may opt to purchase feed from another location where the grain/hay contains greater levels of Se, rather than feeding supplements.
Understanding nutrition is critical for all livestock producers. There is no need for farmers to experience an economic loss due to a nutrient deficiency. Performing tests on your soil and feed can help you identify nutrient needs before problems strike. A little extra initial investment can help you to save in the long run.
Noelle Carroll is a student at Missouri State University. This article was written in conjunction with the 2010 “Feeds and Feeding” Class.


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