CHICAGO — Tyson Foods Inc. (TSN), the nation's largest meat company, on Monday reported better-than-expected quarterly earnings as higher prices for chicken and pork offset the loss of beef exports due to a U.S. case of mad cow disease.

Tyson shares rose to $19.95, the highest level in nearly five years, in trading before the market opened on Monday.

Strong demand for all meat, in part due to the popularity of high-protein diets (search), has helped Tyson and other meat companies overcome the loss of key export markets for beef.

Many foreign buyers, including top buyer Japan, have banned U.S. beef since late December when a Washington state cow tested positive for mad cow disease.

Until then, the United States had been exporting about 10 percent of its beef.

Tyson's net profit for the second quarter ended March 27 rose 65 percent to $119 million, or 33 cents a share, from $72 million, or 20 cents, a year ago.

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