Selenium in the domestic animal nutrition

by

Henning Lyngsø Foged

M.Sc. Agriculture

EU's approval of organic selenium as a fodder-additive as well as the possibility to buy selenium-enriched fertilisers has created much attention among farmers and agricultural advisers. Continued supplementation of the fodder with inorganic selenium is the cheapest way to fulfil the animals' selenium needs, and sufficient in most situations. Regulated use of inorganic selenium can happen in a safe way concerning the environment as well as animals' and human beings' health. Use of organic selenium may be a means to raise the selenium status of animals in the last period of the pregnancy where one otherwise has had problems with this, as the bio-availability is 5-20 % higher than for inorganic selenium. It can, if the legislation prevents more than 20 ppm selenium in mineral mixtures, be of interest to use organic selenium for other animal types as well. Advantages and drawbacks to fertilisation with selenium-enriched fertilisers seems to be insufficiently clarified, and there may possibly be negative effects from this on the environment as well as on human beings' and animals' health. The method is also ineffective and uneconomical and can for the present not be recommended.

Metabolic function of selenium

The function of selenium in the domestic animal nutrition was actually first discovered in 1957, and it was first around 1970 becoming common practice to add selenium to the feed in Denmark. Selenium and vitamin E are both antioxidants because they both protect the membranes from oxidative damage. Due to this shared duty, there is a relationship between the compounds, in which one can substitute for the other in a very small way. For instance, more Se is needed when an animal's vitamin E concentrations are low.

The animals' need for selenium

Domestic animals' minimum needs for selenium is difficult to determine exactly, but is generally considered to be between 0.05 and 0.3 mg per kg dry matter out from the present knowledge base. The following table shows the recommendations from the internationally acknowledged Nutrient Research Council (NRC) in the US.

Table 1: Examples of domestic animals' needs for selenium

MineralCalculator is based on norms published by the Danish National Committee on Cattle Production in cooperation with The Danish Institute of Agricultural Sciences and The Royal Veterinary and Agricultural University (Rapport nr. 84 fra Landsudvalget for Kvæg, August 1999, 47 pp.), which to some extent are based on recommendations from National Research Council (NRC. 1988. Nutrient requirements of Cattle. Nat. Academy Press. Washington DC, 157 pp., and NRC. 1984. Nutrient requirements of Beef Cattle. Nat. Academy Press. Washington DC, 90 pp.).

Selenium content in the crops

The contents of selenium in soils shows a large variation within European countries. It's seen on the map here that there particularly is lack of selenium (darkest areas) in soils in Spain, Poland, northern parts of Germany and the Baltics.

Map showing rough indications of the selenium level in European soils (From https://www.pharmanord.com/history-of-selenium-research

There is also great difference between the selenium contents in different fodder crops. In Denmark for example grain and grass are characterised at selenium contents on less than half of the animals' needs, while concentrates typically contain more selenium than needed, and fish meal 10-30 times the need for selenium.

Legal demands for use of selenium in the feeding

EU Directive 427/2013/EC determines 0.5 mg per kg complete feedingstuff (ppm) with 88% dry matter as the maximal total content of selenium. This equals 0.568 mg/kg dry matter. At total content is understood the natural amount of selenium in the fodder plus the added amount. The individual EU member countries have interpreted a little differently how much selenium that according the Directive is allowed to add to marketed feedstuffs. In Belgium they have until recently only been allowed to use up to 20 mg selenium/kg in mineral mixtures, which is low compared with the importance of selenium for especially Belgian Blue cattle. It is in Norway allowed to market feedstuffs with up to 25 mg selenium per kg, but they have now decided to follow EU's legislation. Great Britain interpret the rules in the way that granulated (powdered) minerals normally contains 20-40 mg selenium/kg, mineral buckets (molassed minerals) 20-30 mg selenium/kg, feed buckets 5-10 mg selenium/kg, and pressed feed blocks 5 mg selenium/kg. The rules are in Denmark interpreted so that most mineral feeds contains 50 mg selenium per kg.

EU has in Regulation 1831/2003⁶ listed both sodium selenite (Na₂SeO₃), sodium selenate (Na₂SeO₄) and organic selenium (seleno-methionine, a yeast product) as feed additives, which means that users, (here under farmers) of those compounds needs to implement HACCP procedures, and that they are not allowed to be fed to animals in the pure form but only via premixtures that are mixed with the ration. The listing of seleno-methionine on EU's list of additives happened with Regulation 1750/2006.

Selenium's negative effects on the environment and the human health

The heavily regulated use of selenium in the feeding are due to the fact that selenium is a dangerous heavy metal that at over-supply brings about serious chronic damages to animals and not least human beings, as we are the last element in the food chain. Selenium is the nutrient with the least distance between the need and the toxic dose; the toxicity level is only about 10 times the need and the deadly dose probably about 100 times the daily need.

Selenium (Se) contamination of agricultural soils and drainage water in California's San Joaquin Valley has been identified as the cause of death and deformation in migratory waterfowl⁴. Other research results and investigations shows that elevated selenium concentrations in the environment causes reproduction disorders and death among fish and bird populations⁵. It is recommended⁵ that the field balance is not exceeding 2 - 7 gram selenium per year due to the ecotoxicologic balance. The health authorities in USA has determined a maximal level of selenium in milk, which in most cases would be exceeded in case the cows were given organic selenium. There are in the literature much discussion about the relation between selenium and cancer; the appearance of cancer can in certain cases be related to an over-supply with selenium.

Conventional supply with selenium via the mineral supplement

Sodium selenite is normally used as selenium source in mineral supplements, and feed norms as well as the legislation is based on that. Problems with selenium deficiencies will normally not appear if the livestock is given access to an adequate mineral supplement, unless the amount of sulphur in the feed ration is unusually high or there are other reasons for higher needs or lower bio-availability.

Use of organic selenium

It was especially due to EU's approval of seleno-methionine in autumn 2006 that focus was turned to use of organic selenium in the feeding. The literature indicates a bio-availability of 35 - 65% for organic selenium, which is 5 to 20% higher than that of inorganic selenium. The organic selenium is, however, very expensive, and each replaced mg of selenium makes one kg feed cost around 1 cent more. This means that it for instance costs € 4 more to give mineral supplements with organic selenium to dry cows, and that the additional price is around € 22 if organic selenium is used the whole lactation cycle.

Use of organic selenium in stead of a similar amount of inorganic selenium makes the deposition of selenium in milk and meat increase substantially, and can give reason for concerns according the above mentioned risks by oversupply with selenium. It is therefore recommended that mineral feedstuffs with organic selenium contains less selenium than mineral feedstuffs with inorganic selenium. Independent research results have not been able to prove that organic selenium as such has any positive effects on health, reproduction or production, but use of organic selenium is a means to boost the selenium status of livestock in the last period of the pregnancy where one otherwise have had problems with this.

Fertilising with selenium enriched fertiliser

Use of selenium enriched fertilisers are common practice in countries like New Zealand and Australia, where they do not have tradition for regularly use of mineral supplements. The method has also been practiced in Finland in the last 20 years. Selenium enriched fertilisers are now available in all EU countries, in Denmark since autumn 2005. Plants do not have any needs for selenium so the selenium fertilising happens with the sole purpose to improve the feed value of the crops.

Research done at Lincoln University in New Zealand reveals, not surprising, that only 15-17% of the selenium has been taken up by the crop², while other researchers^5,9 reports that only 10% is utilised. Selenium fertilising is, with other words, incurring a loss to the environment of 83 - 90%. A positive thing is, however, that the selenium in the crops are on organic form and therefore with a bio-availability of 35 - 65%. The livestock will hence in total be able to utilise as little as app. 10 - 17% x 35 - 65% of the selenium in the fertiliser, or only 3.5 - 11%!!

Two wheat cultivars were grown in the autumn and spring trials at each location in another trial. Grain Se content averaged 0.03 mg/kg in the controls (no Se added), increasing to 0.4–0.5 mg/kg where Se was added at 20 g/ha using the most effective application methods—foliar spray and fertilisers at growth stage 31³, or an increase to a level which far exceeds the needs of the livestock.

Use of selenium enriched fertilisers is therefore not a cost-efficient way to ensure the selenium supplementation of the livestock, and to that comes the fact that selenium is a very expensive mineral. Some farmers uses this method anyway as they consider the method relatively cheap in comparison to the economic losses that selenium deficiencies in their livestock can cause. It costs for instance around € 15 extra per ha to use selenium enriched fertilisers, and if there are 2 cows per ha fodder crops, then the additional cost per cow is only € 7.5. Experience from Finland shows, however, that use of selenium enriched fertilisers require the home grow fodder to be analysed for selenium in order to ensure that the total level of selenium in the ration is not exceeding 0.5 mg/kg. An analysis for selenium costs typically € 20.

There are according Christensen et. al (2007) substantial amounts of selenium in the livestock manure, and the field balance under Danish conditions is from 0.4 to 8.3 g selenium/ha. Use of selenium enriched fertilisers will increase the field balance to 5.2 to 10.2 g/ha, but there are apparently no after effect; the field balance goes into the pool in the soil, which in Denmark is estimated to be around 1 kg selenium per ha⁵.

References

1. National Research Council (NRC). 2001. Nutrient requirements of Dairy Cattle. Seventh revised edition. https://doi.org/10.17226/9825
2. McLaren, R. G. , and L. M. Clucas.2006. A field comparison of pasture selenium uptake from different forms of selenium fertiliser. Lincoln University, Canterbury, New Zealand. New Zealand Journal of Agricultural Research abstracts.
3. Curtin, D. et. al. 2006. Selenium concentration in wheat (Triticum aestivum) grain as influenced by method, rate, and timing of sodium selenate application. New Zealand Institute for Crop & Food Research, Christchurch, New Zealand. New Zealand Journal of Crop and Horticultural Science abstracts.
4. Losi, M. E.; Frankenberger, W. T. Jr. 1997. Bioremediation of selenium in soil and water. Abstract of Soil Science. 162(10):692-702, October 1997.
5. Christensen, Bent Tolstrup et al. 2006. Selenanvendelse i dansk landbrug. Danmarks JordbrugsForskning. DJF Rapport Nr. 125. 64 pp. 
6. Community Register of Feed Additives pursuant to Regulation (EC) No. 1831/2003, Appendix 3 & 4. February 2007, rev. 9.
7. COMMISSION IMPLEMENTING REGULATION (EU) No 427/2013 of 8 May 2013 concerning the authorisation of selenomethionine produced by Saccharomyces cerevisiae NCYC R646 as a feed additive for all animal species and amending Regulations (EC) No 1750/2006, (EC) No 634/2007 and (EC) No 900/2009 as regards the maximum supplementation with selenised yeast. https://eur-lex.europa.eu/eli/reg_impl/2013/427/oj
8. Hasselberger, Sepp. 2006. China: Will Nano Selenium Help Prevent Avian Pandemic? http://www.newmediaexplorer.org/sepp/2006/02/17/china_will_nano_selenium_help_prevent_avian_pandemic.htm
9. Christensen, B. T. , P. Sørensen og O. Aaes. 2007. Selengødskning. Presentation on www.plantekongres.dk
10. National Research Council (NRC). 1996. Nutrient Requirements and Balancing Rations for Horses.
11. National Research Council. 1985. Nutrient Requirements of Sheep, Sixth Revised Edition.