How Much Selenium Does the Cow Need and above all, in what form? By Mark McFarland, Feed Additive Product Manager, Lallemand Animal Nutrition UK & Ireland
Classic selenite, rumen-protected selenite or selenium yeast? What influence does the source of selenium have on the selenium status of dairy cows, dry cows and the transfer to youngstock?
Selenium is an essential
intestine. This mechanism is not found in monogastric animals and
trace element that is now
is solely due to the rumen.
rightly included as standard
As a result, a large proportion of the selenite that is administered
in almost every mineral feed.
to ruminants via mineral feed is simply excreted again. This is directly
Selenium supplementation
reflected in the animals’ selenium status.
has become necessary,
An independent study from Estonia1 showed that, according to
not only because soils, and
KINCAID (1999)3, the selenium status of dairy cows that received
consequently feedstuffs,
only classical sodium selenite via the ration could be classified as
have ever lower selenium
marginally deficient (see Table 1 for selenium reference values for
levels, but also because the challenges faced by livestock are
cows). This status does not automatically mean that diseases will
becoming ever greater.
occur due to a selenium deficiency, but the full potential of selenium,
Selenium plays an important role in various biological processes, e.g. for antioxidant defence against oxidative stress, normal thyroid
particularly with regard to antioxidant defences and its role in the immune system, is not being achieved.
function and optimal reproductive performance. But if selenium is
What does this mean for ruminants? In order to fully exploit the
already used as standard, why are we even talking about it? We now
important positive effects of selenium, the goal should be a beneficial
know that ‘not all selenium is the same’. The choice of selenium source
supply in the upper range of the scale. A classic selenite source cannot
(inorganic selenium or organic selenium) can have a considerable
guarantee this. So, what other options are there?
influence on the selenium status of adult animals, and the possible transfer to offspring via placenta and colostrum, particularly in
Selenized yeast and the rumen
ruminants, due to the influence of the rumen.
Selenized yeast contains organic selenium, mainly in the form of selenomethionine and selenocysteine. These selenium components
The rumen - a blessing and a curse?
are found (albeit in very low levels) in plant protein. This means that
There is no question that the rumen, with its complex microbiota, is
it is a form of selenium that animals have always consumed and
a marvel of nature. It enables the digestion of fibrous plant material
metabolised. Selenite (inorganic selenium), on the other hand, is
that is inedible for other animals, and us humans.
found in the soil and not in plant material, which is why it is not a
However, the rumen poses a real challenge for selenium supply.
natural selenium source for animals.
Classic inorganic selenite, which is very cheap to use, is chemically
The selenium compounds in selenized yeast remain intact in the
reduced in the rumen environment by the influence of microbes to
rumen and are not reduced. This means that they are available for
a form that can no longer be absorbed by the animal in the small
absorption in the small intestine. Some of the selenomethionine is
Table 1: Reference values for whole blood, serum and plasma selenium concentration (µg/l) Deficiency
Marginal deficiency
Adequate supply
Beneficial supply
Oversupply
Reference Kincaid 19993,
a
Whole blood
<60 µg/la
60-200 µg/la
Plasma
<30 µg/l
30-70 µg/l
70-100 µg/l
>100 µg/l
> 200 µg/l
Raven, 20138
Serum
<30 µg/l
30-60 µg/l
60-100 µg/l
>100 µg/l
> 200 µg/l
Raven, 20138
>210 µg/la
Plasma and serum analyses are the most suitable for assessing selenium status.
Page 30 July/August 2024 Feed Compounder
> 400 µg/lb
Yeager et al. 19987
b