Selenium in feedstuffs and rations for dairy cows including a view of the food chain up to the consumer

Selenium (Se) is essential and the recommendation for dairy cows amounts to 0.2 mg Se/kg feed dry matter (DM). Se at high intake is toxic and in the EU a maximum content of 0.5 mg Se/kg complete feed (grain DM equivalent basis of 880 g DM per kg) should not be exceeded. The present study focused on the Se content in important feedstuffs (1), supplementation mainly via mineral vitamin premixes (2) and the analysis of total mixed rations (TMR) (3) for validation of a total Se intake. 201 concentrate feedstuffs and 32 silage samples from grass and green maize, a total of 22 mineral premixes and compound feeds and 413 TMR were analysed for Se by hydride atomic absorption spectrophotometry. Twenty-one mineral premixes (> 40 % ash) were evaluated for Se content and for the expected daily intake according to the labelled recommendation, manufacturers and brands were anonymised. A very low native Se content with a mean of 20-46 mu g Se/kg DM was analysed particularly in grain, grain legumes and silage confirming the necessity for Se supplements. There is an immense range in the Se content of premixes and also in the recommended amounts for daily provision. Increasing the recommended daily intake the premix content of Se has to be decreased significantly. However, the increase of the allowance was stronger than the decrease in Se concentration resulting in an overproportionally higher Se intake at high allowance. The mean Se intake of 8 mg per cow and day via mineral premixes results in 0.4 mg Se per kg DM assuming a total daily feed intake of 20 kg DM per cow. Considering a background Se content in native feedstuffs of about 0.04 mg Se/kg DM, a mean content of 0.44 mg Se per kg total diet DM already covers 75 % of the maximum content of 0.57 mg Se/kg complete feedstuffs DM. Investigations of TMR in Saxon and Thuringian cow herds point to a high intake of Se. According to the present study in dairy cows the Se intake via mineral vitamin premixes may reach or exceed the maximum content of complete feedstuffs according to EU legislation. Too high Se feed contents, particularly via selenised yeasts, will be risky for the consumer (adults; toddlers) who ingests high amounts of Se via Se-enriched milk, meat and eggs which may exceed the upper limit. The ration calculations should be improved according to the recommendations of GfE (Empfehlungen zur Energie- und Nahrstoffversorgung der Milchkuhe und Aufzuchtrinder, DLG-Verlags GmbH, Frankfurt/Main, 2001).