WASHINGTON (Reuters) - U.S.
makers of pet food andall other animal feed will be prevented from
using certain materialsfrom cattle at the greatest risk for spreading
mad cow disease under arule that regulators finalized on Wednesday.

The U.S. Food and Drug Administration, which oversees animal feed, said excludinghigh-risk
materials from cattle 30 months of age or older from allanimal feed
will prevent any accidental cross-contamination betweenruminant feed
(intended for animals such as cattle) and non-ruminantfeed or feed
ingredients.

The new rule takes effect in April, 2009.

Contamination
could occur during manufacture,transport or through the accidental
misfeeding of non-ruminant feed toruminant animals.

Canada
and the United States banned the inclusion ofprotein from cows and
other ruminant animals such as goats and sheep incattle feed in 1997,
following a mad cow outbreak in Britain.

The
measure issued today finalizes a proposed ruleopened for public comment
in October 2005. It goes into effect on April23, 2009.

The
major U.S. safeguards against mad cow disease arethe feed ban, a
prohibition against slaughtering most "downer" cattle-- animals too
sick to walk on their own -- for human food, and arequirement for
meatpackers to remove from carcasses the brains, spinalcords and other
parts most likely to contain the malformed proteinsblamed for the
disease.

Mad
cow disease is a fatal, brain-wasting diseasebelieved to be spread by
contaminated feed. People can contract a humanversion of the disease,
know as Variant Creutzfeldt-Jakob Disease, orvCJD, which scientists
believe can be spread by eating contaminatedparts from an infected
animal.

The
United States has found three cases of mad cowdisease, including the
first on-e detected in December of 2003. Soonafter, U.S. beef exports
were virtually halted. U.S. official have beenslowly working to resume
beef shipments. 

Last week, South
Korea officially announcedit would gradually open its market to U.S.
beef import!s as Washingtonintensifies safety standards.

Eventually,
if all goes well, a full range ofU.S. beef boneless and bone-in, from
animals of any age, would beshipped to a market estimated to be worth
up to $1 billion a year.

(Reporting by Christopher Doering; Editing by David Gregorio)