Re: Selinium requirements

["Duncan Fletcher" <dfletche@gte.net>]

Interesting.

For your 900lb (aprox 400kg) horse eating 20 lb (approx. 9kg). The numbers
as follows:

            Recom        Max      Toxic        LD50

Heide     8-10         n/a           60-90      n/a
Duncan  na             18            n/a          n/a
Susan     na             18             *          1320*
NRC      0.9           18             na         1320
Hart       1              na              2            na
Giffen    0.9           na             80           n/a
UCD     0.3            na             na           n/a

na - no number given in post.
* Susan posted this (3.3 mg/kg body weight) as toxic in her post, but it is
the LD50 number from NRC.

The maximum tolerable level is not the same as toxic. There is some 'safety
factor' in that number. Good studies of actual amounts needed for toxicity
are difficult to perform without sacrificing a lot of horses. LD50 is a
number designating the dosage resulting in 50% fatality (probably over a
specified time period - I don't know the exact details of this common
measure of toxicity). However, that still leaves a huge discrepancy. I will
leave it to others with better access to more recent studies to give them if
the NRC recommendations are outdated.



Duncan Fletcher
dfletche@gte.net

-----Original Message-----
From: Jim Mitchell <navion@lightspeed.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
>