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Abstract: Selenium is an essential trace element in animals and plays a crucial role in animal immunity, growth, and reproduction. However, both excessive and insufficient intake of selenium can harm animals and humans alike. Only through proper selenium intake can we ensure the well-being of both. This article explores diseases and symptoms associated with selenium deficiency and excess in animals and humans, discusses the connection between animal nutrition and immune function, and examines the pathogenesis of nutrient metabolism-related illnesses. It aims to enrich the theory of animal nutritional immunity, establish new standards for the rational use of trace elements, and prevent nutritional metabolic diseases.
Keywords: trace element selenium, health
Selenium (Se) is an essential trace element in animals. It performs multiple physiological functions, including enhancing immunity, promoting growth and development, and supporting reproduction. Selenium supplementation in animal diets can yield positive effects. Nevertheless, either overconsumption or underconsumption of selenium can lead to adverse consequences for animals and humans. Proper selenium intake is vital for maintaining health.
1. Selenium Deficiency and Health
Since 1957, Schwartz and Flotz first confirmed selenium’s ability to prevent liver necrosis and boost the biological growth of humans and animals. Over five decades of research have deepened our understanding of selenium's biological roles. In 1973, the World Health Organization recognized selenium as an essential trace element in human and animal life. Organisms require specific amounts of selenium daily for significant biological impacts. Selenium deficiency often leads to various health issues and diseases.
1.1 Selenium Deficiency and Animal Health
When livestock and poultry lack selenium, they may experience several conditions:
(1) White Muscle Disease: Commonly seen in lambs, yaks, and piglets, this disease features skeletal and myocardial degeneration and necrosis, hence its name derived from the pale appearance of affected muscles. Animals exhibit skeletal and myocardial degeneration with a light color resembling cooked meat, showing yellow-white, gray-yellow, or gray-white stripes. The liver becomes swollen, hard, and brittle with a rough surface and a betel nut-like appearance on the cut surface.
(2) Equine Endemic Proteinuria: A selenium-deficient condition in horses, this disease manifests with dyskinesia, skeletal muscle swelling, heart weakness, and brown sputum. Pathological changes involve degeneration and necrosis of liver and kidney parenchymal organs, along with hemorrhage, edema, and myocardial and skeletal muscle damage.
(3) Camel "Swing Disease": Characterized by movement disorders, this condition in camels results in stiff hindquarters, difficulty walking, and swaying movements. The camel struggles during sharp turns and is prone to falls and fractures. The head and neck tilt to one side, and some muscles tremble. The hind legs spread wide in an "eight" stance.
(4) Yak "Big Belly Disease": Primarily affecting calves in Qinghai Province, this disease causes diarrhea, heart failure, ascites, and pneumonia, resulting in an enlarged belly. Similar to white muscle disease, heart failure is severe, often accompanied by pneumonia and pleurisy.
(5) Subcutaneous Edema in Chicks: A localized selenium-deficient condition causing subcutaneous edema in chicks, marked by yellow or light blue swelling in the head, neck, chest, abdomen, wings, and thighs. Puncture reveals yellow or light blue fluid. Later stages show symptoms like diarrhea, anemia, and lethargy, eventually leading to death. Embryos may also exhibit subcutaneous edema, reducing hatchability.
Other issues include diarrhea in young animals, bovine mastitis, infertility, miscarriages, colibacillosis, pig mulberry heart, fertility decline, embryo degradation, weakened immune function, decreased survival rates of young animals, and slower livestock growth.
1.2 Selenium Deficiency and Human Health
Human selenium deficiency can result in Keshan disease and Kashin-Beck disease, the most prominent manifestations of selenium deficiency in humans. In 1972, Yang Xingyu confirmed that selenium deficiency primarily causes Keshan disease and Kashin-Beck disease. Patients with Kashin-Beck disease showed significantly lower urine selenium concentrations (12 μg/L) compared to non-disease areas (18 μg/L). Average serum selenium levels were less than 11 μg/L in affected areas, while healthy regions had levels around 60-105 μg/L. Keshan disease affects women of childbearing age and preschool children, presenting as congestive heart failure and occasional diffuse cardiac thrombosis leading to sudden death or paralysis. Grain and soil selenium content in affected wards was much lower than in non-disease areas, with daily selenium intake at only 10 μg. Additionally, individuals with low selenium nutrition have higher incidences and mortality rates of coronary heart disease. Those with serum selenium levels below 45 μg/L face a 2-3 times higher risk of coronary heart disease. Selenium deficiency also damages nerve cells and thyroid function and correlates with cancer incidence. High colorectal cancer rates in Jiashan, Zhejiang, relate to low soil selenium content (10 μg/kg) and rice selenium levels (17-37 μg/kg). Research shows that oral cancer, throat cancer, nasopharyngeal cancer, breast cancer, colon cancer, gastrointestinal cancer, liver cancer, lung cancer, esophageal cancer, and others accompany declining blood selenium levels. Selenium levels significantly influence oncogene and anti-oncogene expression. Studies on cretinism also reveal significantly lower serum selenium levels in affected individuals. Long-term selenium-deficient diets impair resistance, digestive system function, neurological health, vision, kidney function, reproductive function, sexual function, and increase risks of over 20 diseases, including malnutrition, cataracts, mastitis, hepatitis, AIDS, infertility, hypertension, and hemolytic anemia.
In conclusion, selenium is indispensable for health. Balancing its intake is critical for preventing deficiencies and toxicities in both animals and humans. Further research and standardization in its usage are essential to maintain optimal health and prevent metabolic diseases.