Dean Foods Co. posted a lower-than-expected quarterly profit as it had to cut prices to compete with private-label brands even as costs for butterfat and other dairy commodities soared, sending its shares down nearly 11 percent.

The largest U.S. dairy company also said Tuesday that Chief Financial Officer Jack Callahan is leaving for another company as of Nov. 30 and will be replaced by Chief Accounting Officer Shaun Mara.

Chief Executive Gregg Engles called Dean's results "disappointing" and said in a statement that its fresh dairy business is expected to "remain challenged as the retail environment continues to be competitive."

"Price concessions that have been given will continue to impact year-over-year comparisons into 2011," Engles said.

He noted that retail prices for private label milk were still far below historic levels.

The company said net earnings were $24.3 million, or 13 cents per share, less than half the $49.7 million profit, or 27 cents per share, of a year earlier.

Analysts on average had been expecting 21 cents per share.

The company expects earnings in the current fourth quarter of between 13 and 18 cents per share.

Engles said Dean Foods would accelerate its cost reduction efforts to cope with the "cost-price squeeze."

Net sales rose 10.6 percent to $3.05 billion, helped by sales growth at its WhiteWave-Alpro business, which sells branded products like Horizon Organic milk and Land O'Lakes creamers.

Shares were down $1.13 off their closing price on Monday, or 10.9 percent, to $9.23 in premarket trading, falling below a yearly low hit in May.