Causes and consequences of selenium deficiency in small ruminants

When feeding livestock, particular attention should be paid to the production, and preparation of fodder, i.e. the meals, while at the same time determining the nutritional requirements in the various production periods. Selenium is an important microelement in animal nutrition. Together with vitamin E, it contributes to the normal functioning of many physical activities, such as the prevention and repair of oxidative cell damage, contributes to the growth and development of young animals, improves reproductive performance, milk quality, improves rumen fermentation and digestibility, and is involved in the body's immune defense. Selenium deficiency in ruminants also results in poor conversion, white muscle disease, and poor wool production and can lead to infertility in sheep. The most important factors that lead to insufficient levels of selenium in animals are fodder production on acidic basalt/granite soils and sandy soils, annual rainfall over 450 mm, predominantly clover pastures, heavy and long-term application of artificial fertilizers, especially fertilizers of sulfur-fortified with superphosphate or gypsum. Selenium deficiency in animals can also be observed in conditions of heat stress, a return to extensive and organic animal husbandry, nutrition imbalance, the presence of elements that are antagonistic to selenium in the ration, and consumption of poor-quality water. The concentration of selenium in the soil, and plant feed in the blood and tissues of animals is a good link to determine its status. The aim of this review is therefore to summarize in what conditions and due to what factors selenium deficiency occurs in animals, what its consequences are.