Organic selenium supplementation increased selenium concentrations in ewe and newborn lamb blood and in slaughter lamb meat compared to inorganic selenium supplementation

1751-0147-50-7 1751-0147 Research Organic selenium supplementation increased selenium concentrations in ewe and newborn lamb blood and in slaughter lamb meat compared to inorganic selenium supplementation Steen Arvid arvid.steen@veths.no Strøm Turid turid.strom@bioforsk.no Bernhoft Aksel aksel.bernhoft@vetinst.no

Department of Production Animal Clinical Sciences, Norwegian School of Veterinary Science, P.O. Box 8146 Dep., NO-0033 Oslo, Norway

Bioforsk Organic Food and Farming Division, Tingvoll gard, NO-6630 Tingvoll, Norway

Department of Toxicology, National Veterinary Institute, Box 8156 Dep., NO-0033 Oslo, Norway

Acta Veterinaria Scandinavica 1751-0147 2008 50 1 7 http://www.actavetscand.com/content/50/1/7 18377659 10.1186/1751-0147-50-7 03 9 2007 31 3 2008 31 3 2008 2008 Steen et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Selenium is part of the antioxidant defence system in animals and humans. The available selenium concentration in soil is low in many regions of the world. The purpose of this study was to evaluate the effect of organic versus inorganic selenium supplementation on selenium status of ewes, their lambs, and slaughter lambs.

Methods

Ewes on four organic farms were allocated five or six to 18 pens. The ewes were given either 20 mg/kg inorganic selenium as sodium selenite or organic selenium as selenized nonviable yeast supplementation for the two last months of pregnancy. Stipulated selenium concentrations in the rations were below 0.40 mg/kg dry matter. In addition 20 male lambs were given supplements from November until they were slaughtered in March. Silage, hay, concentrates, and individual ewe blood samples were taken before and after the mineral supplementation period, and blood samples were taken from the newborn lambs. Blood samples from ewes and lambs in the same pens were pooled. Muscle samples were taken from slaughter lambs in March. Selenium concentrations were determined by atomic absorption spectrometry with a hydride generator system. In the ANOVA model, selenium concentration was the continuous response variable, and selenium source and farm were the nominal effect variables. Two-sample t-test was used to compare selenium concentrations in muscle samples from the slaughtered lambs that received either organic or inorganic selenium supplements.

Results

In all ewe pens the whole blood selenium concentrations increased during the experimental period. In addition, ewe pens that received organic selenium had significantly higher whole blood selenium concentrations (mean 0.28 μg/g) than ewe pens that received inorganic selenium (mean 0.24 μg/g). Most prominent, however, was the difference in their lambs; whole blood mean selenium concentration in lambs from mothers that received organic selenium (mean 0.27 μg/g) was 30% higher than in lambs from mothers that received inorganic selenium (mean 0.21 μg/g). Slaughter lambs that received organic selenium had 50% higher meat selenium concentrations (mean 0.12 mg/kg wet weight) than lambs that received inorganic selenium (mean 0.08 mg/kg wet weight).

Conclusion

Organic selenium supplementation gave higher selenium concentration in ewe and newborn lamb blood and slaughter lamb meat than inorganic selenium supplementation.

Background

Selenium is part of the antioxidant defence system in animals and humans. The selenium concentration in soil is low in many parts of the world including the Nordic countries where it is poorly available because of low soil pH 12345. Animals fed roughage grown in selenium-deficient areas and not supplemented with minerals are vulnerable to oxidant stress. Clinical consequences include ill thrift, reproductive problems, lowered resistance to infectious diseases such as mastitis, and nutritional myopathies 6. Clinical selenium deficiency is rare among humans. In certain areas of China, selenium deficiency predisposes patients to Keshan disease, an endemic viral cardiomyopathy which primarily affects children and young women. In Siberian Russia and China, growing children with selenium deficiency may develop chronic osteoarthropathy (Kashin-Beck disease) 7. However, less-overt selenium deficiencies are probably of more significance. Selenium is required for the proper functioning of the immune system, and appears to be a key nutrient in counteracting the development of virulence and inhibiting HIV progression to AIDS 8. According to experimental animal studies and some observational epidemiological studies in humans, higher selenium intakes might reduce the risk of certain types of cancer 910.

Cereal products and vegetables grown in the Nordic countries, with the exception of Finland, have low selenium content. This contrasts with wheat from North America which has high selenium content and is frequently imported into Norway and Iceland. Feeds to animals in the Nordic countries need to be supplemented with selenium to avoid deficiencies 11112. Selenium intake among humans in Sweden and Denmark is below Nordic Nutrition Recommendations 2004 13. In Norway and Iceland, the selenium intake in humans has been sufficient because of high-selenium wheat imported from North America. This situation could change in Norway because of more home-grown wheat production in recent years.

Pehrson 14 concludes that supplementation of farm animal diets with organic selenium instead of inorganic selenium will increase selenium intake in animals and non-vegetarian humans. The purpose of this investigation was to evaluate the effect of organic versus inorganic selenium supplementation on selenium status in ewe and newborn lamb blood and slaughter lamb meat.

Methods

Farms, Animals, Feeding, and Samples

Sheep from two inland and two coastal organic farms were selected for the trial. On each farm, ewes were randomly allocated into pens of five or six. Each pen received an organically approved mineral supplement containing either 20 mg/kg inorganic selenium as sodium selenite (9 pens), or organic selenium (9 pens). The organic selenium ingredient, mostly selenomethionine, was selenized nonviable yeast produced by Saccharomyces cereviciae 15. The mineral supplements were mixed in a commercial mill.

The sheep were fed a ration which contained grass silage, hay and concentrates. The ewes were given 0.3 to 1.0 kg of concentrates before lambing depending on the number of lambs they were carrying. Grass silage and hay were fed ad libitum. The ewes in each pen consumed 20 g per head of mineral supplement each day on average during the experimental period, which was the last two months before lambing.

The selenium concentrations in silage and hay from all four farms were below 0.05 mg/kg dry matter. Selenium concentrations in the two farms that were located at the coast of Norway were higher (0.03 to 0.05 mg/kg dry matter) than in the two farms located in the inland in Eastern Norway (<0.01 to 0.02 mg/kg dry matter). The selenium concentrations in the roughage were not different from the beginning to the end of the experimental period. Selenium concentrations in concentrates were from 0.17 to 0.57 mg/kg dry matter. Assuming a total dry matter intake of between 1.6 to 1.8 kg per pregnant ewe per day 16, stipulated selenium concentrations in the rations without mineral supplements were between 0.06 to 0.15 mg/kg dry matter; with mineral supplements the total ration selenium concentrations were below 0.40 mg/kg dry matter.

In addition, 20 male lambs on one farm that were too small to be slaughtered in the autumn were given 0.15 kg molasses ensiled barley that was threshed early (50 to 65% dry matter), 0.15 kg commercial concentrates, grass silage ad libitum and free access to mineral supplements up to an average of 20 g per head from November until they were slaughtered in March. The male lambs were randomly allocated to organic selenium supplement (13 lambs) or inorganic selenium supplement (7 lambs) irrespective of the supplementation their mother's had received six months previously. The cause of the skewed distribution between treatments was that the host farmer only had one large and one small pen available for the experiment.

The selenium concentrations in four samples of both the organic selenium and inorganic selenium mineral mixtures were analyzed before being sent to the farmers, and mean concentrations were 19.9 and 23.0 mg selenium/kg, respectively. Silage, hay, concentrates, and individual ewe blood samples were taken just before the mineral supplementation period, and after lambing. Blood samples from ewes in the same pens were pooled before analysis. Blood samples from lambs from mothers in the same pens were taken within the first week post partum and were also pooled before analysis. Blood samples were drawn from the jugular vein (Venoject II, with lithium heparin). The whole blood samples were posted the same day, frozen at arrival the day after and stored until analysis of all samples. Muscle samples from winter-slaughtered male lambs were taken caudoproximally to the carpus, musculus flexor carpi ulnaris.

There are no ethical implications as both groups got selenium supplements.

Analyses

Silage, hay, concentrate, blood and muscle samples were analysed for selenium at the National Veterinary Institute, Norway. Selenium concentrations were determined by atomic absorption spectrometry with a hydride generator system 17, using a Varian SpectrAA-30 with a VGA-76 vapour generation accessory. Before analysis, each sample was prepared by oxidative digestion in a mixed solution with concentrated nitric and perchloric acids, using an automated system with a Tecator 1012 Controller and 1016 Digester heating unit. This method is accredited (NS-EN ISO/IEC 170225). All selenium concentrations were calculated as μg per g blood or feed dry matter; 1 μg/g blood corresponds to 1.052 μg/ml 18. The detection limit was 0.01 μg/g.

Statistics

Selenium concentrations in pooled samples from ewes and newborn lambs were compared between pens receiving mineral supplement with either organic or inorganic selenium using the FIT MODEL platform in JMP (JMP Version 6, SAS Institute Inc., Cary, NC). In the ANOVA-model, selenium was treated as a continuous response variable; and selenium source and farm were nominal (discrete) effect variables. The model was also tested for interaction between selenium source and farm. Two-sample t-test was used to compare selenium concentrations in muscle samples from male lambs that received either organic or inorganic selenium supplements. Differences were declared at the 5% level.

Results

Whole blood selenium concentrations from the sheep in all four farms are plotted in figure 1. There were no differences between pens within farm before the experimental period (mean 0.20 μg/g). After two months with mineral supplements, both groups of ewes had in general higher whole blood selenium concentrations compared to before the experimental period. In addition, ewes that received organic selenium had significantly higher whole blood selenium concentrations (0.28 ± 0.01 μg/g; mean ± SEM) than ewes that received inorganic selenium (0.24 ± 0.02 μg/g). Most prominent, however, was the significant difference in the lambs; lambs from mothers that received organic selenium had nearly 30% higher whole blood selenium concentrations (0.27 ± 0.01 μg/g) than lambs from mothers that received inorganic selenium (0.21 ± 0.01 μg/g).

Figure 1

Whole blood selenium concentrations in ewes before supplementation, and in ewes and their newborn lambs after inorganic or organic selenium supplementation the last two month of pregnancy

Whole blood selenium concentrations in ewes before supplementation, and in ewes and their newborn lambs after inorganic or organic selenium supplementation the last two month of pregnancy. The numbers 1 to 18 corresponds to the pooled blood samples from ewes and lambs in the same pens before and after the supplementation period.

Muscle selenium concentrations from 7 lambs that received inorganic selenium supplement and 13 lambs that received organic selenium are plotted in figure 2. Slaughter lambs that received organic selenium had significantly higher meat selenium concentrations (mean 0.12 mg/kg wet weight) than lambs that received inorganic selenium (mean 0.08 mg/kg wet weight).

Figure 2

Meat selenium concentrations in slaughter lambs after four months of inorganic or organic selenium supplementation

Meat selenium concentrations in slaughter lambs after four months of inorganic or organic selenium supplementation.

Discussion

Organic selenium supplementation gave higher selenium concentrations than inorganic selenium in ewe whole blood (figure 1). This is in accordance with some trials with cattle 1920 and pigs 21, although more equivocal results have been obtained in pigs 2223.

Organic selenium supplementation gave also higher selenium concentrations than inorganic selenium in whole blood of newborn lambs. This is comparable with trials in cattle 24 and pigs 25 that measured selenium concentrations in offspring from mothers fed organic selenium compared to offspring from mothers receiving inorganic selenium. In the cattle trial, however, the calves were sampled after three weeks; the newborn lambs in our experiment were sampled within the first week postpartum.

Organic selenium supplementation gave higher selenium concentrations than inorganic selenium in lamb meat. This increased selenium concentration was highly significant even in this small trial with only 13 plus 7 animals in the organic and inorganic groups respectively. The higher concentration in meat is in accordance with trials that compared organic and inorganic selenium sources in other species; organic selenium was superior to inorganic selenium in increasing the selenium content in meat of cattle 1926 and swine 2728. The male lambs were randomly allocated to organic or inorganic selenium supplement irrespective of what their mothers had received before lambing six months ago. Because the lambs and their mothers did not get any mineral supplements during the six months on pasture, we assume that there was no carry-over effect from the two different selenium sources.

Only two pens with ewes had marginally deficient whole blood selenium concentrations before the supplemental period started (figure 1, pen 1 and 2). There are different definitions of marginal deficiencies in the literature and we chose to use the definition from The National Veterinary Institute in Norway which defines whole blood selenium concentrations between 0.05 to 0.10 μg/g to be marginal. All four farms had participated in an earlier screening of mineral content 1. Thus, the farmers were aware of their low selenium concentrations in soil and roughage and had given their sheep selenium-enriched concentrates and different mineral mixtures, but apparently in varying amounts before the trial started.

Conclusion

Ewes that received organic selenium had significantly higher whole blood selenium concentrations than ewes that received inorganic selenium. Lambs from mothers that received organic selenium had nearly 30% higher whole blood selenium concentrations than lambs from mothers that received inorganic selenium. Organic selenium supplementation gave 50% higher selenium concentration in lamb meat than inorganic selenium supplementations. Our findings support Pehrson's conclusion 14 that supplementation of farm animal diets with organic selenium instead of inorganic selenium will increase selenium status in ewes, newborn lambs and slaughter lambs.

Competing interests

The author(s) declare that they have no competing interests.

Authors' contributions

AS was responsible for blood sampling, coordination of the study, performed the statistical analysis and drafted the manuscript. TS was responsible for feed sampling and coordination of the study. AB was responsible for the selenium analyses. All authors participated in the design of the study, helped to draft the manuscript, and read and approved the final manuscript.

Acknowledgements

Bo Pehrson is acknowledged for help with references, and inspiring feedback during the planning of the trial and drafting of the manuscript.

Status of selenium and vitamin E on Norwegian organic sheep and dairy cattle farms Govasmark E Steen A Strøm T Hansen S Singh BR Bernhoft A Acta Agric Scand A Anim Sci 2005 55 1 40 46 Levels of copper, molybdenum, sulphur, zinc, selenium, iron and manganese in native pasture plants from a mountain area in Southern Norway Garmo TH Frøslie A Høie R Acta Agric Scand 1986 36 147 161 Selenium in Norwegian farmland soils Wu XF Låg J Acta Agric Scand 1988 38 3 271 276 The selenium status of dairy cattle in Estonia Pehrson B Ling K Ortman K Acta Vet Scand 1997 38 4 353 356 9503678 Selenium in soils and plants and its importance in livestock and human nutrition Gissel-Nielsen G Gupta UC Lamand M Westermarck T Adv Agron 1984 37 397 459 Selenium and vitamin E Van Metre DC Callan RJ Vet Clin North Am Food Anim Pract 2001 17 2 373 402 11515407 Selenium. Mineral deficiency and toxicity. Nutritional disorders Merck Manual of Diagnosis and Therapy, Beers MH, Porter RS http://www.merck.com/mmpe/sec01/ch005/ch005i.html The importance of selenium to human health Rayman MP Lancet 2000 356 233 241 10.1016/S0140-6736(00)02490-9 10963212 Lessons from basic research in selenium and cancer prevention Ip C J Nutr 1998 188 1845 1854 Dietary reference intakes for vitamin C, vitamin E, selenium, and carotenoids IOM (Institute of Medicine) Washington , National Academy Press 2000 290 291 Insufficiency of vitamin E and selenium in suckling calves in Norwegian beef herds Bernhoft A Ween H Flåøyen A Geomedical aspects of organic farming Oslo , Norwegian Academy of Science and Letters Steinnes E 2004 133 138 Plasma vitamin E and blood selenium concentrations in Norwegian dairy cows: regional differences and relations to feeding and health Sivertsen T Øvernes G Østerås O Nymoen U Lunder T Acta Vet Scand 2005 46 4 177 1191 1618972 16398330 10.1186/1751-0147-46-177 Nordic Nutrition Recommendations, 4th edition Copenhagen , Norden 2004 436 Organic selenium for supplementation on farm animal diets: it's influence on the selenium status of the animals and on the dietary selenium intake of man Pehrson B Re-defining mineral nutrition Nottingham , Nottingham University Press Taylor-Pickard JA, Tucker LA 2005 253 267 Sel-Plex, Alltech http://www.sel-plex.com Nutrient requirements of sheep, sixth revised edition NRC Washington, D.C. , National Academy Press 1985 vii+99 Precise determination of selenium in tissues using automated wet digestion and an automated hydride generator - atomic absorption spectroscopy system Norheim G Haugen A Acta Pharmacol Toxicol 1986 59 Suppl 7 610 612 3776637 Blood and other body fluids, 3rd printing Altman PL Dittmer DS Bethesda, Maryland , Federation of American Societies for Experimental Biology 1971 Selenite and selenium yeast as feed supplements for dairy cows Ortman K Pehrson B J Vet Med A 1997 44 6 373 380 9342929 The influence of supplements of selenite, selenate and selenium yeast on the selenium status of dairy heifers Ortman K Andersson R Holst H Acta Vet Scand 1999 40 1 23 34 10418193 Selenite and selenium yeast as feed supplements to growing fattening pigs Ortman K Pehrson B J Vet Med A 1998 45 9 551 557 9857833 Evaluating the efficacy of selenium-enriched yeast and sodium selenite on tissue selenium retention and serum glutathione peroxidase activity in grower and finisher swine Mahan DC Parrett NA J Anim Sci 1996 74 12 2967 2974 8994911 Effect of organic and inorganic selenium sources and levels on sow colostrum and milk selenium content Mahan DC J Anim Sci 2000 78 1 100 105 10682808 The influence of dietary selenium as selenium yeast or sodium selenite on the concentration of selenium in the milk of suckler cows and on the selenium status of their calves Pehrson B Ortman K Madjid N Trafikowska U J Anim Sci 1999 77 12 3371 3376 10641886 Long-term effects of dietary organic and inorganic selenium sources and levels on reproducing sows and their progeny Mahan DC Peters JC J Anim Sci 2004 82 5 1343 1358 15144075 Effects of different selenium sources on performance, carcass characteristics, plasma glutathione peroxidase activity and selenium deposition in finishing Hanwoo steers Lee SH Park BY Yeo JM Lee SS Lee JH Ha JK Kim WY Asian-Australasian J Anim Sci 2007 20 2 229 236 Effect of inorganic or organic selenium at two dietary levels on reproductive performance and tissue selenium concentrations in first-parity gilts and their progeny Mahan DC Kim YY J Anim Sci 1996 74 11 2711 2718 8923185 Effects of dietary levels of selenium-enriched yeast and sodium selenite as selenium sources fed to growing-finishing pigs on performance, tissue selenium, serum glutathione peroxidase activity, carcass characteristics, and loin quality Mahan DC Cline TR Richert B J Anim Sci 1999 77 8 2172 2179 10461996