US farm officials came under fresh fire over their estimates of evaporating grain use, with a steep cut to wheat feeding estimates condemned as "a joke" by one trader.

The US Department of Agriculture, in its monthly flagship Wasde report, slashed by 80m bushels to 160m bushels its forecast for US feed use of wheat in 2011-12.

However, the downgrade was not reflected in raised estimates for use of alternative grains, such as corn, for which the feed use estimate was kept steady at 4.7bn bushels.

The disappearance of demand, despite apparently resilient animal numbers, raised fresh question over the USDA's grip on feed consumption of grains, following data two weeks ago showing a surprise rise in inventories of both corn and wheat.

"Where does the USDA get dropping wheat feeding so much without increasing it in corn?" Chicago floor trader Matthew Pierce said.

"Cattle on feed are 105% of last year. This is a joke."

'Demand minimum'

At Teucrium Trading, an issuer of exchange traded products, president Sal Gilbertie, termed Wednesday's estimates "conservative" on corn use.

"Margins on beef and pork producers are healthy, corn ethanol margins are healthy," he told Agrimoney.com.

"If there are any changes in the next couple of month's Wasde reports, we might see demand estimates raised, particularly if corn prices stay at or below $7 a bushel."

Indeed, demand data "could not be reduced much more", without an issue such as global economic meltdown or a collapse in energy prices to change radically consumption dynamics, Mr Gilbertie said.

"At this level, demand is inelastic."

'Price falls overdone'

Consumption figures have taken on extra importance given the apparent stability in US forecasts for crop production.

The USDA kept its estimate for the domestic corn yield at 148.1 bushels per acre, and lowered it for soybeans lowered by a modest 0.3 bushels per acre to 41.5 bushels per acre, despite farm reports that harvests had beaten modest expectations.

Wednesday's data suggest that pressure on corn and soybean prices based on ideas of better-than-expected yields "may have been overdone", University of Illinois agriculture economist Scott Irwin said.

"The supply side of US markets for the current marketing year are basically set. All eyes will now be on indications of demand."