Potential Value of Plants as Sources of New Antifertility Agents II

Publisher Summary This chapter reviews the geomedical aspects of selenium (Se), ranging from the soil through the plants to animal and human nutrition. Selenium has several essential functions in the animal and human body, and interactions occur with other elements and compounds. The beneficial effects of Se are obtained at different concentration levels, depending on the functions of Se and on interacting factors such as vitamin E, fatty acids, and sulfur. The nutritional minimum level for animals and humans is about 0.05–0.10 ppm Se in dry fodder/food, and intake below that cause severe deficiency diseases. At somewhat higher levels of Se intake, there are indications of a protective effect toward a number of human diseases, and toxic effects of Se occur with exposure to levels of 2–5 ppm Se or more, depending on the chemical form of the Se. Selenium toxicity in livestock is known in a few areas around the world, but Se deficiency has turned out to be much more common than Se toxicity. The Se deficiency problem is severe in New Zealand, in parts of China, in parts of North America, and in the Scandinavian countries.

Selenium in Soils and Plants and its Importance in Livestock and Human Nutrition

Nutrient requirements of all livestock are based on the size of the animal, how active the animal is, the body growth rate, and/or the animal’s level of milk production and fat content in milk produced. Maintenance requirements are for low levels of activity as when being fed in a dry lot situation. When animals are on pasture activity increases and these the requirements may be as much as 25% higher due to this increased activity.

Nutrient Requirements of Sheep

The purpose of this review article is to demonstrate the close parallelism of daily requirements, biological activity and minimum and maximum tolerable levels of selenium for animals and man. In addition, the carcinogenic/anticarcinogenic properties of selenium are discussed and a postulate of how these dichotomous effects may occur in accordance with selenium-induced immunomodulation is presented. A review of pertinent literature pertaining to the biological action of selenium in animals and man, including deficiency, toxicity, carcinogenicity and effects on immunity, is included to support these concepts. The predominant biochemical action of selenium in both animals and man is to serve as an antioxidant via the selenium-dependent enzyme, glutathione peroxidase, and thus protect cellular membranes and organelles from peroxidative damage. The signs and symptoms of selenium deficiency closely simulate each other for animals and man. Severe deficiency is characterized by cardiomyopathy while moderate deficiency results in less severe, myodegenerative syndromes such as muscular weakness and pain as well as a variety of other selenium-associated diseases. Clinical manifestations of many of these disorders require contributory factors, such as stress, to precipitate symptoms which are documented for animals and implicated for humans. Current evidence suggests that a daily selenium consumption for man of approximately 30 micrograms is necessary to prevent the selenium-deficient syndrome, Keshan disease, while approximately 90 micrograms/day/adult should be the minimum daily requirement for optimum biological performance. Recognizing that humans in several countries do not meet the proposed minimum daily requirement of 90 micrograms, several compelling reasons are presented in deriving this minimal daily nutritional intake. Selenosis can occur in laboratory animals, livestock, and humans following long-term exposure to selenium concentrations as low as 5 mg selenium/kg of diet (5 ppm). The selenium-induced lesions for all species are similar, which once again illustrates a positive corollary for selenium effects in both animals and man. From compilation of available data, the maximum tolerable level for selenium in man could be considered in the range of 1000 to 1500 micrograms/day. This is in contrast to the currently recommended maximum human tolerable level of 500 micrograms/day. The amount of selenium that can be tolerated, however, is dependent upon individual biological variation, nutritional status and general state of health.(ABSTRACT TRUNCATED AT 400 WORDS)

The Two Faces of Selenium-Deficiency and Toxicity--Are Similar in Animals and Man

Trace element deficiencies and fertility in ruminants: a review.

Trials conducted in South Australia, in an area where pasture improvement by means of the introduction of subterranean clovers has been practised for 10-15 years, have shown a significant improvement in fertility, in ewes treated with selenium. Analysis of all pastures grazed, and of whole blood of stock grazing them, indicated that the selenium status of the feed and of the animals was low. Phyto-oestrogen assays showed the presence of the isoflavones formononetin, genistein, and biochanin A, in the subterranean clover, which was mainly the cultivar Yarloop (Trifolium subterraneum L. var. Yarloop). Administration of selenium four to eight weeks before mating, given either as an oral dose of sodium selenite, or supplied in the form of an intraruminal selenium pellet containing elemental selenium and iron, led to an improvement in fertility; in some cases from 49 to 76 per cent. Also, lamb mortality was reduced by selenium administration to the ewes. There were differences due to selenium administration (P<0.001). Ewe fertility differed between pastures designated 'oestrogenic' and 'non-oestrogenic' (P<0.05). But no interaction between selenium and the presence of phyto-oestrogens could be shown by these experiments. The results are discussed in relation to the problem of infertility associated with the grazing of improved pastures

R. E. Kuchel

Papers

The effect of selenium on infertility in ewes grazing improved pastures