Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our thesis.

What: Shares of Dean Foods Co. (NYSE:DF) were going sour today, falling as much as 11% after a disappointing fourth-quarter earnings report.

So what: The dairy maker posted adjusted earnings of $0.18 per share, a penny below estimates, while sales fell off 7% to $2.3 billion, essentially in line with estimates at $2.29 billion. Though the company's share of U.S. fluid milk sales improved from 34.9% in the third quarter to 35.7%, industrywide volumes fell 2.2% and the company's year-over-year volume sales dropped 9% due to the loss of business from a major retailer. Adjusted for that loss and another customer vertically integrating its operations, Dean's volumes declined 0.6%, better than the industry average of 1.7%, though it may be foolish to overlook disappearing customers in a declining industry.

Now what: Dean's outlook for the current year was even less encouraging, as the dairy producer said, "The consensus view of the dairy commodity outlook for 2014 appears to be more challenging than previously expected as current dairy commodity prices have moved near or beyond all-time highs." Dairy demand is falling in the U.S as consumers turn toward soy milk and other healthier alternatives, and the company last year spun off WhiteWave, the organic division that was its growth engine, so there's little reason to expect sales to increase. Add to that nearly $1 billion in debt and the recent cut in food stamps, and it's hard to see a reason that Dean shares would bounce back anytime soon.

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Jeremy Bowman has no position in any stocks mentioned. The Motley Fool owns shares of WhiteWave Foods. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.