Updated: US stocks slip at midday; Wal-Mart leads retailers lower

NEW YORK — Stocks are edging lower in midday trading after several companies posted disappointing results. Wal-Mart Stores led the Dow Jones industrial average lower Thursday with a 5 percent decline after the giant retailer cut its sales forecast. Perrigo, a drugmaker, and the cable channel operator Discovery Communications also stumbled after releasing disappointing results. […]