From:
pjdutche
Date: 2002-04-15 17:44:00 UTC
Subject: wet/dry food nutrition (Re: Baby ferret nursing
formula????)
--- In Ferret-Health-list@y..., daneedv@a... wrote:
> Anyway, you can't compare dry food percentages to moist food
> percentages without doing a conversion. Because most of us feed
> dry food, we usually talk about protein and fat requirements as
> needed in dry foods.
That's right... The thing is, to make comparisons between wet and
dry foods, you have to convert to values on a dry-matter basis.
Basically this involves accounting for the water, which is a large
volume of a canned food. Hill's has already done this on their
website, so that's convenient:
http://www.prescriptiondiet.com/product/feline_ad.asp
A/D is a high-protein, high-fat food... Note that on their website,
they are more specific than they are on their labels, where they give
minimum and maximum values.
In case anyone is curious about how to make the dry-matter conversion
of values on a label of food, it's pretty easy. You just have to
account for the water, so you need to be sure you have the percent
moisture in order to make your calculations. Taking the A/D example,
using *label* values rather than the more-accurate website values
(they don't give percent moisure on the website), here are the basics
we start with:
Crude protein min 8.5%
Crude fat min 5.25%
Moisture max 78%
So, 78% of what is in the can is just water. Subtract 78% from 100%,
and you are left with 22%. That is, 22% of what is in the can is
*not* water. It is the dry matter.
Now, 8.5% of what is in the can is protein. Next, we have to figure
out what percent 8.5 is of 22. That will tell us what percentage of
the dry matter in a can of a/d is protein. So, 8.5/22=0.386
(38.6%).
Fat works the same way. 5.25% of the can of A/D is fat, and 22% is
dry matter. So, 5.25/22=0.2386 (23.86%).
So, based on their labels, we can say that on a dry-matter basis, A/D
is:
Crude protein min 38.6%
Crude fat min 23.86%
Their website gives more accurate values, so we can get away from the
minimum figures. The website says A/D is 45.7% protein and 28.7% fat
on a dry-matter basis.
Anyway, hope that helps explain how these numbers work. Also remember that even dry kibble has some moisture (say around 10%), so to really compare foods to one another, ideally, everything would be corrected to a dry-matter basis. In reality, most people don't bother with it, since kibbles mostly have about the same amount of moisture and typically it's a kibble to another kibble comparison.
Cheers,
-Pam S.