The makers of Greenies, the nation's top-selling dog treat, are rolling out a newly formulated version they say is easier for dogs to chew and digest. The change comes months after a series of lawsuits and media reports claimed the treat sometimes sickened or killed dogs. Officials with S&M NuTec--a Kansas City-based company that was acquired earlier this year by candy maker Mars Inc.--said they had been working on a new formula even before the negative publicity, but acknowledged that they hope the updated Greenies win back skittish pet owners. Greenies are hard, dark green treats shaped like a bone on one end and a toothbrush on the other. The company claims the treats help scrub the dog's teeth, preventing periodontal disease and freshening the animal's breath. Market research firm Euromonitor International said Greenies represented almost 20 percent of the U.S. dog treat market in 2005.