Animal and Aquacultural Sciences
Can we achieve the same selenium concentrations in chicken muscle as in fish?
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The trace element selenium prevents many types of cancer, cardiovascular diseases and allergies, and helps to generally strengthen our immune system. But how can we secure the intake of sufficient amounts of selenium? – Well, recent research shows that in the future, chicken meat can be a good selenium source!
Selenium is important for human health. A sufficient supply of selenium is important for the prevention of many types of cancer, cardiovascular diseases and allergies, for generally strengthening our immune system and for protection against the toxic effects of heavy metals such as mercury and cadmium. There is increasing concern about the low intake of selenium, not only in Norway, but in many other parts of the world, e.g., most western European countries, parts of Australia, New Zealand, Asia and Africa. The recommended daily allowance (RDA) of selenium in the Nordic countries is 40 µg/day for women and 50 µg/day for men. This intake level is sufficient to ensure the saturation of a selenium-containing enzyme (glutathione peroxidase-3), which is found in human plasma. However, animal tests show that there is a considerable gap between the minimum requirement for selenium, defined as the dose needed to prevent selenium deficiency, and the concentrations needed to ensure the maximum preventive effect against cancer, protection against tissue damage due to oxygen deficiency and the stimulation of immunological functions. This agrees with geographical epidemiological studies in the USA, in which the geographical patterns for cancer mortality (all cancer types) and mortality from heart diseases (especially heart attacks and high blood pressure) seem to coincide with geographical variations in selenium intake. Selenium intake in states with low selenium levels, where both cancer and heart disease mortality were highest, was about twice as high as the current Nordic RDA for selenium. Selenium intake in states with the highest selenium levels (where mortality was lowest) was 5-6 times higher than the current RDA in the Nordic countries.
Earlier, cereals were an important source of selenium for the inhabitants of Norway, since much of the grain was imported from the US Midwest. The US grain was high in selenium – the USDA food tables listed a content of 707 µg selenium pr kg wheat. In contrast, Norwegian wheat only contains about 20 µg selenium per kg. As an increasing share of Norwegian bread grain is being grown domestically, cereals are no longer the major source of selenium for the country’s inhabitants.
Fish is another good selenium source, containing 300-500 µg selenium per kg. However, the per-capita consumption of fish in Norway is lower than the consumption of meat. We thus wished to see if it is possible to raise the selenium concentration in chicken muscles to the level of the trace element in fish.
The content of selenium in animal products depends on the selenium contents of the feed. In food tables, chicken is listed with a selenium concentration of about 100 µg/kg.
We performed feeding trials on broilers in the winters of 2005 and 2006. The project is funded by the Research Council of Norway, and Dr. Trine Sogn (Dept. of Plant and Environmental Sciences, UMB) is the project coordinator.
Day-old chicks were fed wheat-based diets with varying selenium contents. The feed was produced at ForTek in Ås. Whereas some of the diets included wheat that was grown under varying selenium-fertilizing regimes, others included the addition of varying amounts of organic selenium compounds (selenium-enriched yeast). Selenium contents in the diets of the two trials varied between 37 and 870 µg selenium/kg feed.
The chicks were slaughtered when they were three weeks old, and blood and tissue samples taken. We analyzed glutathione peroxidase activity in blood. The chickens were not like humans, where enzyme saturation occurs at considerably lower intake levels. In the chicks, enzyme activity increased even when selenium intake was quite high (see fig).
The same results were found in the chicken leg muscle. With increasing selenium intake, the selenium concentration in broiler meat also increased (see fig.). Animals with the lowest dietary selenium intake also had the lowest selenium concentration in the muscles (46 µg /kg muscle), whereas those fed 870 µg selenium per kg feed nearly had 400 µg per kg muscle.
Thus, considering the question asked in the title: Yes – it is possible to produce broilers with the same selenium concentration as fish.
Updated: 14.05.09Printerfriendly version
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