DALLAS — Shares of Dean Foods Co. slid 13 percent in premarket trading Tuesday after the dairy producer reported worse-than-expected results and trimmed its guidance because of competitive pressures.

The Dallas-based company reported second-quarter earnings of $17.6 million. Adjusted profit was 21 cents per share, which fell short of the average estimate of 30 cents per share, according to Zacks Investment Research.

Dean Foods posted revenue of $1.93 billion, which also missed forecasts.

“In the second quarter, we faced a challenging and rapidly evolving retail environment,” CEO Ralph Scozzafava said. “We experienced volume pressure from both a macro and competitive perspective that impacted our total volume performance.”

Dean Foods now expects to earn 80 cents to 95 cents per share this year versus the average FactSet forecast of $1.29 per share.