Selenium as an essential nutrient: the case for supplementation in ruminant nutrition to improve animal health and human nutrition.

Abstract Selenium (Se) is an essential element in animal nutrition and metabolism. Research began with the study of Se toxicity, followed years later by the study of its deficiency; however, problems caused by Se deficiency are the most common. Several studies have investigated the effect of Se on the antioxidant and immune systems. Livestock animals, especially those reared in intensive management systems, are subjected to high levels of oxidative stress that can affect health, performance and the quality and stability of meat and milk. Part of those studies have used doses above the recommended intake and found positive responses, particularly in the immune system of ruminants. The objective of this review was to describe the function of Se as an essential nutrient and its effect on the metabolism, and to discuss the need to revise the recommendations for ruminant nutrition to values slightly above the nutritional requirements, but always below toxic levels, so that Se can exert its full function in the organism and improve animal health and human nutrition.