THE SELENIUM CONTENT OF FINNISH FORAGE CROPS

H. E. Oksanen and Markus Sandholm

College of Veterinary Medicine, Department of Medicine, Helsinki

Received April 3, 1970

The importance of selenium in plants was first realised in the 1930’5, when it was
found that »alkali disease» and »blind staggers» ofcattle and horses in the United States
of America were caused by the animals eating plants containing a high concentration of
selenium (Beath el al. 1934). The biological significance of selenium was believed to be
restricted to its toxicity until Schwarz and Foltz (1957) showed that Factor-3, which
protects rats against liver necrosis, was a selenium compound. It was subsequently estab-
lished that selenium is an essential trace element which will protect animals against a
variety of diseases that were previously thought to be due primarily to vitamin E deficiency
(Schwarz 1961). One of the most important diseases of farm animals, now known to be
associated with a low selenium intake, is nutritional muscular degeneration (NMD) in
ruminants.

Research in many countries has shown that NMD in ruminants is associated with
low selenium concentrations in the diet (Hartley & Grant 1961, Gardiner el al. 1962,
Allaway & Hodgson 1964). This in turn has stimulated the development of accurate
methods ofmeasuring small amounts of selenium in biological material (Wolf et al. 1963,
Watkinson 1966, Lindberg 1968).

In Finland, NMD in cattle has caused considerable economic losses (Andersson 1960,
Oksanen 1965), and although the results of selenium treatment have generally been good,
there have been conflicting reports on the selenium content of forage plants in Ostro-
bothnia, where the disease was once most common (Andersson 1960,Westermarck 1964,
Oksanen 1965). In view of this, it was considered important to re-examine the selenium
content of Finnish forage plants collected from different parts of the country.

Material and Methods

During the crop years 1968 and 1969, 145 plant samples were collected from 13 dif-
ferent field stations belonging to the Agricultural Research Centre in Finland. The samples
were ground and their dry weights determined. The selenium content ofsamples weighing
10—25 g was determined by the method of Lindberg (1968). The material was wet-ashed
with a mixture of nitric and perchloric acids, the selenium extracted with toluene 3,4-
dithiol, and 2,3-diaminonaphthalene was used as a fluorescing reagent. The recovery



251

of the selenium was measured by using Se 75 as a tracer, the radioactivity being measured
with a Nal-crystal computer before and after handling.

Results
The results are set out in Table I. The mean concentration of selenium in hay and

grain samples was 0.014 ppm (14 ppb) and 0.007 ppm (7 ppb), respectively. The samples
with the highest concentration came from the most northerly station at Rovaniemi. There
was no correlation between the selenium content in the plants and the type of soil in which
the plants were grown.

Table 1. Selenium content (p.p.b*) in forage (dry matter).

Barley Rye Oat Wheat Timothy Clover Pasture Pea Rape
Locality of grasses
field station nxs nxs nxs nxs nxs nxs nxs fsL s nxs
Anjala 17 413 111 26 ±2 17
Kokemäki 17 1 13 1 85 IJ4 1 12
Laukaa 4 3 ±4 1 2 2 3 ±1 5 17±16 4 18±14 5 8 ±4
Maaninka 2 3 ±3 1 2 17 15
Mietoinen 1 1J 16
Mikkeli 13 17 115 47 ±1 28 ±2 2 10±1
Mouhijärvi 1 6 29 ±6 311 ± 1 18
Pello 46 ±2 14 12
Pälkäne 1 4 1 5 24 ±1 3 15±4 3 22±6 3 12±4 1 3
Rovaniemi 3 13±15 1 18 1 7 5 39±26 3 19±7 3 48±23 143
Ruukki 6 3 ±1 1 4 2 3 ±1 8 12±4 6 10±3
Tohmajärvi 2 7 ±4 2 6 ±0 5 8 ±1 1 12 10 10±3
Ylistaro 2 2 ±1 1 5 27 ±4 3 8 ±2

*p.p.b. = parts per billion or micrograms per kilogram of dry matter.

Discussion
The low selenium values obtained in this study are similar to those reported from other

countries in forage known to cause selenium deficiency diseases in animals. Oldfield et al.
(1963) reported that they could provoke NMD in lambs with a hay-oat diet containing
less than 0.02 ppm Se and that the disease was prevented, when the selenium concen-
tration was raised to 0.06 ppm. Most of the field cases of selenium responsive diseases in
ruminants have occurred in young lambs and calves from dams that have been kept on
feeds containing less than 0.05 to 0.10 ppm Se (Allaway et al. 1967). The observed
critical minimum levels of selenium required in animal diets vary from less than 0.03 to
0.3 ppm Se (Allaway et al. 1967).

In preliminary investigations it was found that hay samples collected in 1965 from
South-Ostrobothnia contained 0.01 to 0.02 ppm Se, while hay samples collected previously
from the same area contained 0.013 to 0.081 (mean 0.032) ppm Se. A barley sample
contained 0.014 and an oat sample less than 0.010 ppm Se (Oksanen 1965) These results
were obtained by the use of neutron activation analysis and the accuracy was restricted
by the low power of the reactors used. The fluorescence method used in the present study
is suitable for determining low selenium contents in biological material (Watkinson 1966),



252

and the use of the Se 75 tracer, to measure the loss of selenium during the analysis, increases
the reliability of the method.

Low selenium content in plants is not necessarily related to the soil selenium content,
as selenium in the soil may occur in forms that the plant cannot utilize. For example in
acid environments compounds of selenium and iron may occur, from which plants are
unable to absorb selenium (Trelease & Beath 1949). Likewise, the content of sulphur
in the soil affects the availability of selenium to the plant (Hurd-Karrer 1934).

In Finland, especially in Ostrobothnia, there are acid »sulphate soils» rich in iron
and sulphur (Kivinen 1950) and it is possible that this may account for the low selenium
content of plants in this area. However, it is known that the plutonic and metamorphic
rock in the whole country is especially low in selenium, about 0.06 ppm (Koljonen 1965).
Consequently it appears that the low soil selenium content is the main reason for the low
selenium values in forage plants in Finland.

The selenium responsive diseases are not necessarily simple selenium deficiencies.
Vitamin E, unsaturated fatty acids, sulphur containing amino acids and possible other
factors, are involved. For example in Ostroborhnia, where NMD was a common disease
prior to selenium supplementation, it was found that yearly fluctuations in incidence could
be related to variations in the vitamin E content ofhay, which was dependent on harvesting
conditions (Oksanen 1965, Thafvelin & Oksanen 1966). Notwithstanding this complex
aetiology, NMD can be prevented and cured by selenium.

From the results of the present study it would appear that the selenium content of
hay and grain in Finland is so low' that selenium responsive diseases may be expected
to occur anywhere in the country unless selenium supplementation is practised.

Summary
The total of 145 plant samples were collected from 13 field stations in Finland

during the crop years 1968 and 1969 and analysed for selenium by a fluorescence
method using 2,3-diaminonaphthalene as the fluorescing reagent. The loss of selenium
during analysis was measured by a Se75 tracer.

The selenium content of all samples was very low. The mean value for hay samples
was 0.014 ppm (range 0.002 to 0.048), and for grain sarnies 0.007 ppm (range 0.002
to 0.085). The samples with the highest selenium content came from Lapland (Rova-
niemi), where the mean values for hay and grain were 0.036 ppm and 0.013 ppm
respectively. There was no correlation between the plant selenium content and soil type.

It appears that selenium deficiency diseases may occur anywhere in Finland unless
Se supplementation is carried out.

Acknowledgements: This work received financial assistance from the State
Medical Committee. The radioactivity measurements were carried out in the Isotope
Laboratory, Faculty of Agriculture and Forestry, University of Helsinki.

REFERENCES

Allaway, W. H., Cary, E. E. & Ehlig, C. F. 1967. The cycling of low levels of selenium in soils, plants
and animals. Selenium in Biomedicine, First Intern. Symposium, AIV Publish, Comp., p. 273
296.



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Allaway, W. H. & Hodgson, J. F. 1964. Selenium in forages as related to the geographic distribution of
muscular dystrophy in livestock. J. Anim. Sci. 23: 271—277.

Andersson, P. 1960. Nutritional muscular dystrophy in cattle with special reference to the functional
state of the thyroid. Acta path.microbiol.scand., suppl. 134.

Beath, O. A., Draize, J. H., Eppson, H. F., Gilbert, C. S. & Mc Creary, O. C. 1934. Certain poisonous
plants of Wyoming activated by selenium and their association with respect to soil types. J. Am.
Pharm. Assoc. Sci. Ed. 23: 94—97.

Gardiner, M. R., Armstrong, J., Fels, H. & Glencross, R. N. 1962. A preliminary report on selenium
and animal health in Western Australia. Aust. J. exp. Agric. Anim. Hubs. 2: 261—269.

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Fed. Proc. 20: 679—688.

Hurd-Karrer, A-M. 1934. Selenium injury to wheat plants and its inhibition by sulphur. J. agric. Res.
49: 343—357.

Kivinen, E. 1944. Sulfat- eller alunjordar, deras egenskaper och synpunkter pä deras odling. Sv. Vall-
och Mosskulturför. T. 2: I—l3.

Koljonen, T. 1965. Seleenin esiintymisestä suomalaisissa kivissä. Unpublished thesis. Arch, of Geology
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Oksanen, H. . 1965. Studies on nutritional muscular degeneration (NMD) in ruminants. Ibid, suppl. 2.
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J. Agric. Food. Chem. 11: 388 —390.
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drying conditions. J. Dairy Sci. 49: 282—286.
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SELOSTUS

REHUJEN SELEENIPITOISUUS MAASSAMME

H. E. Oksanen ja Markus Sandholm

Eläinlääketieteellinen korkeakoulu, Sisätautiopin laitos, Helsinki

Vuosien 1968 ja 1969 sadoista eri puolilta maata sijaitsevilta koeasemilta kerätyn 145 kasvinäytteen
seleenipitoisuus määrättiin fluoresenssimenetelmällä käyttäen 2,3- diaminonaftaleiinia ja kontrolloimalla
tapahtuneet seleenitappiot Se76 -lisällä.

Seleenipitoisuus oli erittäin alhainen kaikissa näytteissä (Taulukko 1). Keskiarvo heinänäytteissä oli
o,ol4ppm (ääriarvot 0,002 ja0,048) sekä viljanäytteissä 0,007 ppm (ääriarvot 0,002 ja0,085). Keskimäärin
korkeimmat seleeniarvot todettiin Perä-Pohjolan (Rovaniemi) koeasemalta kerätyissä näytteissä. Kasvu-
alustan maaperän ja kasvien seleenikonsentraation välillä ei voitu osoittaa korrelaatiota.

Todetuista erittäin alhaisista seleeniarvoista voidaan päätellä, että seleenin puutteen aiheuttamia koti-
eläinten tauteja saattaa esiintyä kautta koko maan, mikäli seleenitarvetta ei ole tyydytty erityisellä sclce-
nilisällä.