Severe Selenium Deficiency in Georgia Soils, Forages, and Animals

Summary

Based on relevant literature on selenium contents of soils and crops, and the selenium nutrition status of animals, we hypothesized that selenium deficiency in Georgia soils and forages could be more severe than what has been perceived so far. In response, we conducted a survey of selenium contents of soils and forages in Georgia. The results provided solid evidence of severe selenium deficiency in both soils and forages regardless of geographical regions, and soil and forage types, proving the hypothesis. This vital information was incorporated in an extension publication to help researchers, extension educators, forage producers, and animal entrepreneurs to better manage selenium deficiency.

Situation

Selenium is one of at least 17 essential minerals needed in animal diets. It is a part of several essential enzyme systems that provide vital human and animal health benefits as an antioxidant in physiological processes. The most severe clinical sign of selenium deficiency in animals is called white muscle disease, which results in degeneration and necrosis in both skeletal and cardiac muscles. Selenium deficient animals often die of cardiac failure. Another more common consequence is poor reproductive performance as a result of an increased early embryonic death and retained placentas. Selenium deficiency also results in lack of immunity, and reduced milk and meat production. In the existing literature, the geographical coincidence of selenium deficiency in animals and low selenium contents of forages and grains used as feed in the U.S. suggests that adequate selenium concentrations in feedstuffs are important in preventing selenium related health problems in animals. Inorganic selenium supplementation (feeding sodium selenite salt), as adopted in 61% of the beef cattle farms in the Southeast, does not eliminate selenium deficiency (because the animals actually require organic forms of selenium such as selenomethionine). The animals may still suffer from mild and chronic selenium deficiency that is often not recognized. Hence it is a hidden problem that reduces animal performance and profitability. Furthermore, food crops produced on the selenium deficient soils as well as meat, milk, and eggs from the selenium deficient animal industry in the state may contain insufficient selenium to provide adequate selenium required for sound human health. Though it is an essential micronutrient in animal and human diets, selenium is also toxic to animals and humans when too much is consumed; therefore, it merits special attention in animal feeding to ensure that the concentration range is appropriate. As far as Georgia soils are concerned, the nationwide study of Cary et al (1967) classified the coastal region of the state as selenium deficient based on a very limited number of samples. The regional distribution map of forage and grain selenium contents in the United States and Canada (NRC, 1983) classified the coastal region of Georgia as a low selenium area where about 80% of the grains and forages were found to be selenium deficient. In the rest of Georgia, about 50% of the grains and forages were considered selenium deficient. However, these studies were limited by the number of samples and may be inaccurate.

Response

We conducted a survey of selenium contents of soils and forages in the state. Georgia soils were found critically deficient in selenium regardless of geographic region and soil type. The forages produced across the state were also found deficient in selenium regardless of forage and soil types. Thus, selenium deficiency in Georgia soils and forages is much more severe and widespread than assumed. Information about the existence of selenium deficiency in Georgia soils and forages, the role of selenium in animal nutrition, disorders resulting from selenium deficiency or toxicity, various methods of selenium supplementation, and recommendations for selenium management in Georgia were incorporated in an extension publication as an educational resource. Further research and education programs are underway by the UGA team.

Impact

Out of 39 soil samples from various counties, only one had an adequate level of selenium (0.5-0.9 mg/kg). Most of the rest were very low (<0.3 mg/kg) and a few were low (0.3-0.5 mg/kg) in selenium content. Likewise out of 39 forage samples, 25 were clearly deficient (<0.1 mg/kg), 11 were marginally deficient (0.1-0.2 mg/kg), and only 3 were adequate (>0.2 mg/kg) in selenium content. A further detailed study with 60 samples representing 5 different forage species from one county revealed that 92-100% of the samples in various forages species were deficient in selenium; 32% of the samples were even below the limit of quantification (0.014 mg/kg); the overall mean selenium concentration was about 10-fold lower than the adequate level. Thus, the survey determined that selenium deficiency in Georgia soils and forages is much more severe than indicated by the previous limited scale national study. Combating selenium deficiency with a holistic vision into the soil-plant-animal systems through an appropriate research and education program would support a healthy and productive animal industry as well as offer tremendous human health benefits such as increased immunity, prevention of cancers and/or delayed progression of cancers, and others.

State Issue

Food, Nutrition and Health

Details

• Year: 2012
• Geographic Scope: State
• County: Clarke
• Program Areas:
  • Agriculture & Natural Resources