Re: Selenium requirements

[Susan Evans Garlinghouse <suendavid@worldnet.att.net>]

Heya Jim,

One of the things to keep in mind about nutrition is that it's not an
exact science.  There are alot of variables that can make x number of mg
for one animal toxic while being deficient for another.  Size of the
animal, absorptive efficiency, performance level, source of the selenium
(or whatever), etc.  There are also alot of nutritive factors that
affect how an animal will respond to a particular mineral---for example,
there is some evidence that feeding linseed meal with high doses of
selenium seems to have some protecting effect against selenium toxicity
(THIS IS NOT A SUGGESTION TO GO FEED A BUNCH OF LINSEED MEAL TO YOUR
HORSE SO HE DOESN'T GET SELENIUM TOXICITY, FOLKS!!!).  Exactly how and
with what feeds you supply Se also affects the amount of Se that gets
into the bloodstream as well.  Get the picture?

Regarding the different numbers from different sources---my numbers
(from several different sources) and Heidi's are close enough as far as
I'm concerned to be ballparked together.  There ARE some areas in which
NRC is considered outdated, but my understanding is that selenium levels
aren't one of them.  The original data was from a number of good studies
that aren't any less valuable just because they're ten or fifteen years
old.  You can always add more information, but new information does not
ALWAYS have to discredit earlier data.  Also, out of curiousity, I
emailed Skip Hintz, one of the editors of the NRC book(s) and he thinks
the Se requirements are still valid as well.

Lay publications (as in the ones that are published for the general
public, not the scientific community)(and no flames are implied here) I
don't tend to place as much value in unless I know the author's
credentials and their sources.  Courtney I know has a Ph.D in I think
chemistry or physics (can't remember for sure, but we had a great
discussion about the crystalline structures of enteroliths) and is no
dummy, so in his case I'd like to hear more about why he recommends the
numbers he does.  The other lay publication, well, I dunno.

The UCD publication is probably based on good, probably more recent
data.  When they say small excesses may be toxic, I think they're
probably saying what I said in my first paragraph---one horse's bread is
another horse's poison.  However, let's use some common sense here---if
brand shiny new data stated that only a few mgs per day causes toxicity,
why aren't there horses all over the country having Se toxicity problems
after decades of being fed at much higher levels?  I'm not a DVM that
spends all day looking at horses, but my understanding is that Se
toxicity problems are fairly rare without trying real hard, as Heidi
pointed out.  And just hay alone from a non-Se-deficient area (let alone
grain mixes that have Se added) would provide an amount of Se
considerably over what some of these sources are considering "toxic". 
So I have some doubts that such low levels are really all that toxic.

In my opinion (humble or otherwise), selenium poisoning is pretty easily
avoided by just not over-feeding it as a mineral supplement, UNLESS your
vet specifically tells you to feed at a certain level.  99% of the
mineral imbalances in animals (and humans) occur because an owner is so
concerned about providing enough of one mineral or vitamin that they
overdo and mess up the balance of all the other nutrients that are
affected or are antagonistic to the supplemented nutrient.  Your best
bet is not to try to mess around too much with specific vitamin and
mineral levels by yourself unless you happen to have a degree in it.   I
don't mean for this to sound stuffy, but it IS easy to cause more
problems than you solve---I DO have degree(s) in it, and _I_ don't mess
around with specific levels without a d*** good reason.  If you think
your hay is deficient in Se, check with an extension agent.  If it is,
fine.  Either supplement with a complete grain mix that already has a
balanced vit-min pack added, or add a small amount of vit-min supplement
yourself, and DON'T exceed the recommended dosages.  99% of the time,
you'll be providing everything you need in sufficient quantities and
won't be anywhere near toxic levels.  Where you ARE likely to get into
trouble is adding a dose of this supplement plus a dose of that
supplement, plus a handful of that one over there and a cup of this one
that was on sale.  More is not better, and there are NUMEROUS nutrients
which can reach toxic levels if overfed.  At best, you're making
expensive pee puddles.  At worst, you're causing harm.

See ya,

Susan Garlinghouse



Jim Mitchell wrote:
> 
> I can't seem to find agreement on the amount of selenium a horse needs and what is
>  toxic. Below I have summarized information from posts to this group and some books.
>     I have calculated the required and toxic amounts below for a 900 lb horse eating 20
>  lb.s of food per day.
> 
>  Heidi Smith DVM says 8 to 10 mg/day is correct and 60 to 90 mg/day will cause chronic
>  toxicity
> 
>  Susan Garlinghouse says 2mg/kg of diet which is 16 mg/day, almost twice Heidi's for my
>  horse.  Susan says toxic is 3.3mg/kg of body weight which is over 1200mg/day
> 
>  Duncan Fletcher quotes NRC which matches Susan's recommended amount.
> 
>  Courtney Hart's new book says .11mg/100 lb of body weight or 1 mg/day recommended
>     Courtney states .22 can be low level toxic or 2mg/day can be cause chronic toxicity.
>                  This value is 1/5 to 1/10 what Susan & Heidi recommend
> 
>  Horse Owner's Vet Handbook (Giffin & Gore) pg373 states .1mg/kg of diet or .83mg/day
>  recommended for my horse. 5mg/kg is toxic or 41 mg/day is toxic
> 
>  The UCD Book of Horses states .3ppm in the diet is recommended which calcs out to 2.5
>  mg/day for my horse. It says "relatively small excesses may be toxic"
> 
>     Anyway you can see that what some people recommend is considered toxic by others.
> The UCD book is new and I have heard the NRC values may be outdated?  Any comments?
> 
>  Jim Mitchell
> 
> Sorry if this appears twice but it didn't seem to go through the first time.  Jim
> 
>     ---------------------------------------------------------------
> 
> Subject: Selinium requirements
> Date: Wed, 21 Jan 98 01:47:30 +0000
> From: Jim Mitchell <navion@lightspeed.net>
> To: ridecamp@endurance.net
> 
> I can't seem to find agreement on the amount of selinium a horse needs and what is
> toxic. Below I have summarized information from posts to this group and some books.
>    I have calculated the required and toxic amounts below for a 900 lb horse eating 20
> lb.s of food per day.
> 
> Heidi Smith DVM says 8 to 10 mg/day is correct and 60 to 90 mg/day will cause chronic
> toxicity
> 
> Susan Garlinghouse says 2mg/kg of diet which is 16 mg/day, almost twice Heidi's for my
> horse.  Susan says toxic is 3.3mg/kg of body weight which is over 1200mg/day
> 
> Duncan Fletcher quotes NRC which matches Susan's recommended amount.
> 
> Courtney Hart's new book says .11mg/100 lb of body weight or 1 mg/day recommended
>    Courtney states .22 can be low level toxic or 2mg/day can be cause chronic toxicity.
> This value is 1/5 to 1/10 what Susan & Heidi recommend
> 
> Horse Owner's Vet Handbook (Giffin & Gore) pg373 states .1mg/kg of diet or .83mg/day
> recommended for my horse. 5mg/kg is toxic or 41 mg/day is toxic
> 
> The UCD Book of Horses states .3ppm in the diet is recommended which calcs out to 2.5
> mg/day for my horse. It says "relatively small excesses may be toxic"
> 
>    Anyway you can see that what some people recommend is considered toxic by others. The
> UCD book is new and I have heard the NRC values may be outdated?  Any comments?
> 
> Jim Mitchell