U.S. corn futures are expected to open lower Thursday on profit-taking and lackluster demand at current high price levels.

Traders expect Chicago Board of Trade futures to open 3 to 5 cents lower. In overnight trade, corn for September delivery slipped 3 3/4 cents to $7.28.

While traders continue to hear troubling news about the U.S. crop, prices are already historically high, and demand has been relatively weak.

"From a supply standpoint we're contracting," said Jason Britt, president of Central States Commodities in Kansas City. "From a demand standpoint, we're stagnant."

Weekly export sales within analysts' modest expectations Thursday. The U.S. Department of Agriculture reported net sales of 536,100 metric tons for all crop years. Traders were expecting sales between 350,000 and 700,000.

The sales included 58,600 metric tons to China, which had previously been categorized under "unknown destinations."

The downturn in demand is to some extent seasonal, analysts say. With harvest approaching, end-users of corn have reason to wait until new supplies enter the pipeline, which typically weighs on prices.

The market is also facing technical resistance, some traders say. While the December contract has set new contract highs for three consecutive days, traders say the market could be challenged to top $7.50 unless there is some fresh supportive news.

But Britt said corn has not had the explosive rally, and precipitous drop, seen in the gold market recently, which has caused some analysts to say a top has been set in that market.

"It doesn't feel like we've had the blow-off," he said. "Setbacks seem to be bought."

Results from the Pro Farmer Midwest crop tour continue to reaffirm traders' worries about the crop. The tour projected Illinois' corn yield at 156 bushels an acre based on surveys of fields. That was down from the tour's 2010 estimate of 166.5 bushels an acre and the three-year average of 166.9 bushels an acre.

The declining U.S. corn prospects prompted the International Grains Council on Thursday to lower its world corn production forecast to 849 million tons, down 10 million.

Analysts say that traders could be wary of tacking on long positions ahead of a key speech by Federal Reserve Chairman Ben Bernanke in Wyoming on Friday. The concern, they say, is that markets could fall if he doesn't indicate new stimulus policies.