Dean Food Co. struggled with a glut of milk in the second quarter, obliging the dairy giant to cut prices on the private-label products that make up much of its milk and ice-cream sales. Even though consumers are paying less, they didn’t buy more milk, contributing to what Dean Foods said on Monday was an 8.2% drop in second-quarter revenue to $1.85 billion. Analysts expected profit to fall, but Dean Foods’ earnings announcement still sent shares down as much as 8% in early trading. They regained some ground to close Monday’s session at $18.16, a drop of 3.5%.