Hi Todd,

>The grass of grass-fed ruminants would include the seeds at the top 
>of the stalks in any case, at least when the grass is mature.  Those 
>grains, which are a completely natural part of the animal's diet, 
>would contain gliadin/gluten.

Gluten is just found in wheat, barley, rye (and oats). Grasses are a 
different family.
http://www.kintera.org/site/pp.asp?c=ewK0LjP7E&b=83967

>So if the premise is that an animal must have a completely 
>gluten-free diet for its meat to be gluten-free

Grass fed meat does not cause me to get arthritis, carpel tunnel, 
itchy rashes and Restless Leg Syndrome.
Even farmed wild animals are eating grains:
http://www.fsis.usda.gov/Fact_Sheets/Farm_Raised_Game/index.asp

>  feedlot cattle tend to be "finished" on corn and soy meal.

(soy can give similar symptoms to gluten):
http://www.glutenfreeforum.com/index.php?showtopic=9515

Paleobest,
Susan