Ridecamp: Re: [RC] [RC] B.C.A.A. Complex

Pray tell us how you determine
what is a "normal amount?"

Jim--

There are a couple of ways you can approach this.One is to design a diet
that is (hopefully) completely deficient in that nutrient, and comparing the
animals' performance on that control diet to animals receiving diets with
varying levels of the nutrient.  Another possibility is to run a
digestibility trial of sorts, where you again control the amounts of the
nutrient, but you measure the appearance of the nutrient in the feces (or
urine, where appropriate), which should be an indication that the animal's
needs are being met and excess is being eliminated from the body.  This
version makes the assumption that all amino acids that disappear are
absorbed and utilized as amino acids.

What has to be taken into consideration by the researcher is that fecal
material always contains protein/amino acids that don't come from the feed
but are endogenous.  Endogenous (for the folks who are sitting there saying
"There she goes with the science lingo again") means that the protein (or
lipid, or carbohydrate, or whatever) came from the body rather than the
feed.  In the horse, this is primarily from the cells which slough off the
intestinal wall (it renews itself every few days) and bacterial protein.
You account for this by determining the amount that appears in the manure of
the control group to establish a base line.  Then, anything above that
amount is considered to be dietary in origin.

These sort of trials are not exactly the most glamorous sort of research---I
speak from experience!  However, it is pretty much the only way to establish
nutritional requirements for something like protein or energy.  Done
properly, they are time-consuming but effective methods of determining
requirements.

If you want to determine normal circulating amounts in the blood, or rate of
absorption from the gut, you can use a nutrient that is labeled with a
marker of some sort.  Frequently, this is accomplished by replacing a
hydrogen atom with a tritium (radioisotope of hydrogen) on the molecule.

The main thing that to be remembered is that for something to be considered
a valid determination of a dietary requirement, there has to be ample data
and statistical analyses to meet tradtitional scientific standards.  It also
has to be repeatable....otherwise it stands a chance of ending up in the
Journal of Irreproducible Results (a real publication...we used to pass them
around the grad student office!).


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